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llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
Sanjoy Das fcb3ff9afd [RS4GC] Use OB_deopt instead of "deopt" 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258529 91177308-0d34-0410-b5e6-96231b3b80d8
2016-01-22 19:20:40 +00:00

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//===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Rewrite an existing set of gc.statepoints such that they make potential
// relocations performed by the garbage collector explicit in the IR.
//
//===----------------------------------------------------------------------===//
#include "llvm/Pass.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Statepoint.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#define DEBUG_TYPE "rewrite-statepoints-for-gc"
using namespace llvm;
// Print the liveset found at the insert location
static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden,
cl::init(false));
static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden,
cl::init(false));
// Print out the base pointers for debugging
static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden,
cl::init(false));
// Cost threshold measuring when it is profitable to rematerialize value instead
// of relocating it
static cl::opt<unsigned>
RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden,
cl::init(6));
#ifdef XDEBUG
static bool ClobberNonLive = true;
#else
static bool ClobberNonLive = false;
#endif
static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live",
cl::location(ClobberNonLive),
cl::Hidden);
static cl::opt<bool> UseDeoptBundles("rs4gc-use-deopt-bundles", cl::Hidden,
cl::init(false));
static cl::opt<bool>
AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info",
cl::Hidden, cl::init(true));
/// Should we split vectors of pointers into their individual elements? This
/// is known to be buggy, but the alternate implementation isn't yet ready.
/// This is purely to provide a debugging and dianostic hook until the vector
/// split is replaced with vector relocations.
static cl::opt<bool> UseVectorSplit("rs4gc-split-vector-values", cl::Hidden,
cl::init(false));
namespace {
struct RewriteStatepointsForGC : public ModulePass {
static char ID; // Pass identification, replacement for typeid
RewriteStatepointsForGC() : ModulePass(ID) {
initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
bool runOnModule(Module &M) override {
bool Changed = false;
for (Function &F : M)
Changed |= runOnFunction(F);
if (Changed) {
// stripNonValidAttributes asserts that shouldRewriteStatepointsIn
// returns true for at least one function in the module. Since at least
// one function changed, we know that the precondition is satisfied.
stripNonValidAttributes(M);
}
return Changed;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
// We add and rewrite a bunch of instructions, but don't really do much
// else. We could in theory preserve a lot more analyses here.
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
}
/// The IR fed into RewriteStatepointsForGC may have had attributes implying
/// dereferenceability that are no longer valid/correct after
/// RewriteStatepointsForGC has run. This is because semantically, after
/// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire
/// heap. stripNonValidAttributes (conservatively) restores correctness
/// by erasing all attributes in the module that externally imply
/// dereferenceability.
/// Similar reasoning also applies to the noalias attributes. gc.statepoint
/// can touch the entire heap including noalias objects.
void stripNonValidAttributes(Module &M);
// Helpers for stripNonValidAttributes
void stripNonValidAttributesFromBody(Function &F);
void stripNonValidAttributesFromPrototype(Function &F);
};
} // namespace
char RewriteStatepointsForGC::ID = 0;
ModulePass *llvm::createRewriteStatepointsForGCPass() {
return new RewriteStatepointsForGC();
}
INITIALIZE_PASS_BEGIN(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
"Make relocations explicit at statepoints", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_END(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
"Make relocations explicit at statepoints", false, false)
namespace {
struct GCPtrLivenessData {
/// Values defined in this block.
DenseMap<BasicBlock *, DenseSet<Value *>> KillSet;
/// Values used in this block (and thus live); does not included values
/// killed within this block.
DenseMap<BasicBlock *, DenseSet<Value *>> LiveSet;
/// Values live into this basic block (i.e. used by any
/// instruction in this basic block or ones reachable from here)
DenseMap<BasicBlock *, DenseSet<Value *>> LiveIn;
/// Values live out of this basic block (i.e. live into
/// any successor block)
DenseMap<BasicBlock *, DenseSet<Value *>> LiveOut;
};
// The type of the internal cache used inside the findBasePointers family
// of functions. From the callers perspective, this is an opaque type and
// should not be inspected.
//
// In the actual implementation this caches two relations:
// - The base relation itself (i.e. this pointer is based on that one)
// - The base defining value relation (i.e. before base_phi insertion)
// Generally, after the execution of a full findBasePointer call, only the
// base relation will remain. Internally, we add a mixture of the two
// types, then update all the second type to the first type
typedef DenseMap<Value *, Value *> DefiningValueMapTy;
typedef DenseSet<Value *> StatepointLiveSetTy;
typedef DenseMap<AssertingVH<Instruction>, AssertingVH<Value>>
RematerializedValueMapTy;
struct PartiallyConstructedSafepointRecord {
/// The set of values known to be live across this safepoint
StatepointLiveSetTy LiveSet;
/// Mapping from live pointers to a base-defining-value
DenseMap<Value *, Value *> PointerToBase;
/// The *new* gc.statepoint instruction itself. This produces the token
/// that normal path gc.relocates and the gc.result are tied to.
Instruction *StatepointToken;
/// Instruction to which exceptional gc relocates are attached
/// Makes it easier to iterate through them during relocationViaAlloca.
Instruction *UnwindToken;
/// Record live values we are rematerialized instead of relocating.
/// They are not included into 'LiveSet' field.
/// Maps rematerialized copy to it's original value.
RematerializedValueMapTy RematerializedValues;
};
}
static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) {
assert(UseDeoptBundles && "Should not be called otherwise!");
Optional<OperandBundleUse> DeoptBundle =
CS.getOperandBundle(LLVMContext::OB_deopt);
if (!DeoptBundle.hasValue()) {
assert(AllowStatepointWithNoDeoptInfo &&
"Found non-leaf call without deopt info!");
return None;
}
return DeoptBundle.getValue().Inputs;
}
/// Compute the live-in set for every basic block in the function
static void computeLiveInValues(DominatorTree &DT, Function &F,
GCPtrLivenessData &Data);
/// Given results from the dataflow liveness computation, find the set of live
/// Values at a particular instruction.
static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data,
StatepointLiveSetTy &out);
// TODO: Once we can get to the GCStrategy, this becomes
// Optional<bool> isGCManagedPointer(const Type *Ty) const override {
static bool isGCPointerType(Type *T) {
if (auto *PT = dyn_cast<PointerType>(T))
// For the sake of this example GC, we arbitrarily pick addrspace(1) as our
// GC managed heap. We know that a pointer into this heap needs to be
// updated and that no other pointer does.
return (1 == PT->getAddressSpace());
return false;
}
// Return true if this type is one which a) is a gc pointer or contains a GC
// pointer and b) is of a type this code expects to encounter as a live value.
// (The insertion code will assert that a type which matches (a) and not (b)
// is not encountered.)
static bool isHandledGCPointerType(Type *T) {
// We fully support gc pointers
if (isGCPointerType(T))
return true;
// We partially support vectors of gc pointers. The code will assert if it
// can't handle something.
if (auto VT = dyn_cast<VectorType>(T))
if (isGCPointerType(VT->getElementType()))
return true;
return false;
}
#ifndef NDEBUG
/// Returns true if this type contains a gc pointer whether we know how to
/// handle that type or not.
static bool containsGCPtrType(Type *Ty) {
if (isGCPointerType(Ty))
return true;
if (VectorType *VT = dyn_cast<VectorType>(Ty))
return isGCPointerType(VT->getScalarType());
if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
return containsGCPtrType(AT->getElementType());
if (StructType *ST = dyn_cast<StructType>(Ty))
return std::any_of(ST->subtypes().begin(), ST->subtypes().end(),
containsGCPtrType);
return false;
}
// Returns true if this is a type which a) is a gc pointer or contains a GC
// pointer and b) is of a type which the code doesn't expect (i.e. first class
// aggregates). Used to trip assertions.
static bool isUnhandledGCPointerType(Type *Ty) {
return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty);
}
#endif
static bool order_by_name(Value *a, Value *b) {
if (a->hasName() && b->hasName()) {
return -1 == a->getName().compare(b->getName());
} else if (a->hasName() && !b->hasName()) {
return true;
} else if (!a->hasName() && b->hasName()) {
return false;
} else {
// Better than nothing, but not stable
return a < b;
}
}
// Return the name of the value suffixed with the provided value, or if the
// value didn't have a name, the default value specified.
static std::string suffixed_name_or(Value *V, StringRef Suffix,
StringRef DefaultName) {
return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str();
}
// Conservatively identifies any definitions which might be live at the
// given instruction. The analysis is performed immediately before the
// given instruction. Values defined by that instruction are not considered
// live. Values used by that instruction are considered live.
static void analyzeParsePointLiveness(
DominatorTree &DT, GCPtrLivenessData &OriginalLivenessData,
const CallSite &CS, PartiallyConstructedSafepointRecord &result) {
Instruction *inst = CS.getInstruction();
StatepointLiveSetTy LiveSet;
findLiveSetAtInst(inst, OriginalLivenessData, LiveSet);
if (PrintLiveSet) {
// Note: This output is used by several of the test cases
// The order of elements in a set is not stable, put them in a vec and sort
// by name
SmallVector<Value *, 64> Temp;
Temp.insert(Temp.end(), LiveSet.begin(), LiveSet.end());
std::sort(Temp.begin(), Temp.end(), order_by_name);
errs() << "Live Variables:\n";
for (Value *V : Temp)
dbgs() << " " << V->getName() << " " << *V << "\n";
}
if (PrintLiveSetSize) {
errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n";
errs() << "Number live values: " << LiveSet.size() << "\n";
}
result.LiveSet = LiveSet;
}
static bool isKnownBaseResult(Value *V);
namespace {
/// A single base defining value - An immediate base defining value for an
/// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'.
/// For instructions which have multiple pointer [vector] inputs or that
/// transition between vector and scalar types, there is no immediate base
/// defining value. The 'base defining value' for 'Def' is the transitive
/// closure of this relation stopping at the first instruction which has no
/// immediate base defining value. The b.d.v. might itself be a base pointer,
/// but it can also be an arbitrary derived pointer.
struct BaseDefiningValueResult {
/// Contains the value which is the base defining value.
Value * const BDV;
/// True if the base defining value is also known to be an actual base
/// pointer.
const bool IsKnownBase;
BaseDefiningValueResult(Value *BDV, bool IsKnownBase)
: BDV(BDV), IsKnownBase(IsKnownBase) {
#ifndef NDEBUG
// Check consistency between new and old means of checking whether a BDV is
// a base.
bool MustBeBase = isKnownBaseResult(BDV);
assert(!MustBeBase || MustBeBase == IsKnownBase);
#endif
}
};
}
static BaseDefiningValueResult findBaseDefiningValue(Value *I);
/// Return a base defining value for the 'Index' element of the given vector
/// instruction 'I'. If Index is null, returns a BDV for the entire vector
/// 'I'. As an optimization, this method will try to determine when the
/// element is known to already be a base pointer. If this can be established,
/// the second value in the returned pair will be true. Note that either a
/// vector or a pointer typed value can be returned. For the former, the
/// vector returned is a BDV (and possibly a base) of the entire vector 'I'.
/// If the later, the return pointer is a BDV (or possibly a base) for the
/// particular element in 'I'.
static BaseDefiningValueResult
findBaseDefiningValueOfVector(Value *I) {
// Each case parallels findBaseDefiningValue below, see that code for
// detailed motivation.
if (isa<Argument>(I))
// An incoming argument to the function is a base pointer
return BaseDefiningValueResult(I, true);
if (isa<Constant>(I))
// Constant vectors consist only of constant pointers.
return BaseDefiningValueResult(I, true);
if (isa<LoadInst>(I))
return BaseDefiningValueResult(I, true);
if (isa<InsertElementInst>(I))
// We don't know whether this vector contains entirely base pointers or
// not. To be conservatively correct, we treat it as a BDV and will
// duplicate code as needed to construct a parallel vector of bases.
return BaseDefiningValueResult(I, false);
if (isa<ShuffleVectorInst>(I))
// We don't know whether this vector contains entirely base pointers or
// not. To be conservatively correct, we treat it as a BDV and will
// duplicate code as needed to construct a parallel vector of bases.
// TODO: There a number of local optimizations which could be applied here
// for particular sufflevector patterns.
return BaseDefiningValueResult(I, false);
// A PHI or Select is a base defining value. The outer findBasePointer
// algorithm is responsible for constructing a base value for this BDV.
assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
"unknown vector instruction - no base found for vector element");
return BaseDefiningValueResult(I, false);
}
/// Helper function for findBasePointer - Will return a value which either a)
/// defines the base pointer for the input, b) blocks the simple search
/// (i.e. a PHI or Select of two derived pointers), or c) involves a change
/// from pointer to vector type or back.
static BaseDefiningValueResult findBaseDefiningValue(Value *I) {
assert(I->getType()->isPtrOrPtrVectorTy() &&
"Illegal to ask for the base pointer of a non-pointer type");
if (I->getType()->isVectorTy())
return findBaseDefiningValueOfVector(I);
if (isa<Argument>(I))
// An incoming argument to the function is a base pointer
// We should have never reached here if this argument isn't an gc value
return BaseDefiningValueResult(I, true);
if (isa<Constant>(I))
// We assume that objects with a constant base (e.g. a global) can't move
// and don't need to be reported to the collector because they are always
// live. All constants have constant bases. Besides global references, all
// kinds of constants (e.g. undef, constant expressions, null pointers) can
// be introduced by the inliner or the optimizer, especially on dynamically
// dead paths. See e.g. test4 in constants.ll.
return BaseDefiningValueResult(I, true);
if (CastInst *CI = dyn_cast<CastInst>(I)) {
Value *Def = CI->stripPointerCasts();
// If stripping pointer casts changes the address space there is an
// addrspacecast in between.
assert(cast<PointerType>(Def->getType())->getAddressSpace() ==
cast<PointerType>(CI->getType())->getAddressSpace() &&
"unsupported addrspacecast");
// If we find a cast instruction here, it means we've found a cast which is
// not simply a pointer cast (i.e. an inttoptr). We don't know how to
// handle int->ptr conversion.
assert(!isa<CastInst>(Def) && "shouldn't find another cast here");
return findBaseDefiningValue(Def);
}
if (isa<LoadInst>(I))
// The value loaded is an gc base itself
return BaseDefiningValueResult(I, true);
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
// The base of this GEP is the base
return findBaseDefiningValue(GEP->getPointerOperand());
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
// fall through to general call handling
break;
case Intrinsic::experimental_gc_statepoint:
llvm_unreachable("statepoints don't produce pointers");
case Intrinsic::experimental_gc_relocate: {
// Rerunning safepoint insertion after safepoints are already
// inserted is not supported. It could probably be made to work,
// but why are you doing this? There's no good reason.
llvm_unreachable("repeat safepoint insertion is not supported");
}
case Intrinsic::gcroot:
// Currently, this mechanism hasn't been extended to work with gcroot.
// There's no reason it couldn't be, but I haven't thought about the
// implications much.
llvm_unreachable(
"interaction with the gcroot mechanism is not supported");
}
}
// We assume that functions in the source language only return base
// pointers. This should probably be generalized via attributes to support
// both source language and internal functions.
if (isa<CallInst>(I) || isa<InvokeInst>(I))
return BaseDefiningValueResult(I, true);
// I have absolutely no idea how to implement this part yet. It's not
// necessarily hard, I just haven't really looked at it yet.
assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
if (isa<AtomicCmpXchgInst>(I))
// A CAS is effectively a atomic store and load combined under a
// predicate. From the perspective of base pointers, we just treat it
// like a load.
return BaseDefiningValueResult(I, true);
assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are "
"binary ops which don't apply to pointers");
// The aggregate ops. Aggregates can either be in the heap or on the
// stack, but in either case, this is simply a field load. As a result,
// this is a defining definition of the base just like a load is.
if (isa<ExtractValueInst>(I))
return BaseDefiningValueResult(I, true);
// We should never see an insert vector since that would require we be
// tracing back a struct value not a pointer value.
assert(!isa<InsertValueInst>(I) &&
"Base pointer for a struct is meaningless");
// An extractelement produces a base result exactly when it's input does.
// We may need to insert a parallel instruction to extract the appropriate
// element out of the base vector corresponding to the input. Given this,
// it's analogous to the phi and select case even though it's not a merge.
if (isa<ExtractElementInst>(I))
// Note: There a lot of obvious peephole cases here. This are deliberately
// handled after the main base pointer inference algorithm to make writing
// test cases to exercise that code easier.
return BaseDefiningValueResult(I, false);
// The last two cases here don't return a base pointer. Instead, they
// return a value which dynamically selects from among several base
// derived pointers (each with it's own base potentially). It's the job of
// the caller to resolve these.
assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
"missing instruction case in findBaseDefiningValing");
return BaseDefiningValueResult(I, false);
}
/// Returns the base defining value for this value.
static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) {
Value *&Cached = Cache[I];
if (!Cached) {
Cached = findBaseDefiningValue(I).BDV;
DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> "
<< Cached->getName() << "\n");
}
assert(Cache[I] != nullptr);
return Cached;
}
/// Return a base pointer for this value if known. Otherwise, return it's
/// base defining value.
static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) {
Value *Def = findBaseDefiningValueCached(I, Cache);
auto Found = Cache.find(Def);
if (Found != Cache.end()) {
// Either a base-of relation, or a self reference. Caller must check.
return Found->second;
}
// Only a BDV available
return Def;
}
/// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
/// is it known to be a base pointer? Or do we need to continue searching.
static bool isKnownBaseResult(Value *V) {
if (!isa<PHINode>(V) && !isa<SelectInst>(V) &&
!isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) &&
!isa<ShuffleVectorInst>(V)) {
// no recursion possible
return true;
}
if (isa<Instruction>(V) &&
cast<Instruction>(V)->getMetadata("is_base_value")) {
// This is a previously inserted base phi or select. We know
// that this is a base value.
return true;
}
// We need to keep searching
return false;
}
namespace {
/// Models the state of a single base defining value in the findBasePointer
/// algorithm for determining where a new instruction is needed to propagate
/// the base of this BDV.
class BDVState {
public:
enum Status { Unknown, Base, Conflict };
BDVState(Status s, Value *b = nullptr) : status(s), base(b) {
assert(status != Base || b);
}
explicit BDVState(Value *b) : status(Base), base(b) {}
BDVState() : status(Unknown), base(nullptr) {}
Status getStatus() const { return status; }
Value *getBase() const { return base; }
bool isBase() const { return getStatus() == Base; }
bool isUnknown() const { return getStatus() == Unknown; }
bool isConflict() const { return getStatus() == Conflict; }
bool operator==(const BDVState &other) const {
return base == other.base && status == other.status;
}
bool operator!=(const BDVState &other) const { return !(*this == other); }
LLVM_DUMP_METHOD
void dump() const { print(dbgs()); dbgs() << '\n'; }
void print(raw_ostream &OS) const {
switch (status) {
case Unknown:
OS << "U";
break;
case Base:
OS << "B";
break;
case Conflict:
OS << "C";
break;
};
OS << " (" << base << " - "
<< (base ? base->getName() : "nullptr") << "): ";
}
private:
Status status;
AssertingVH<Value> base; // non null only if status == base
};
}
#ifndef NDEBUG
static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) {
State.print(OS);
return OS;
}
#endif
namespace {
// Values of type BDVState form a lattice, and this is a helper
// class that implementes the meet operation. The meat of the meet
// operation is implemented in MeetBDVStates::pureMeet
class MeetBDVStates {
public:
/// Initializes the currentResult to the TOP state so that if can be met with
/// any other state to produce that state.
MeetBDVStates() {}
// Destructively meet the current result with the given BDVState
void meetWith(BDVState otherState) {
currentResult = meet(otherState, currentResult);
}
BDVState getResult() const { return currentResult; }
private:
BDVState currentResult;
/// Perform a meet operation on two elements of the BDVState lattice.
static BDVState meet(BDVState LHS, BDVState RHS) {
assert((pureMeet(LHS, RHS) == pureMeet(RHS, LHS)) &&
"math is wrong: meet does not commute!");
BDVState Result = pureMeet(LHS, RHS);
DEBUG(dbgs() << "meet of " << LHS << " with " << RHS
<< " produced " << Result << "\n");
return Result;
}
static BDVState pureMeet(const BDVState &stateA, const BDVState &stateB) {
switch (stateA.getStatus()) {
case BDVState::Unknown:
return stateB;
case BDVState::Base:
assert(stateA.getBase() && "can't be null");
if (stateB.isUnknown())
return stateA;
if (stateB.isBase()) {
if (stateA.getBase() == stateB.getBase()) {
assert(stateA == stateB && "equality broken!");
return stateA;
}
return BDVState(BDVState::Conflict);
}
assert(stateB.isConflict() && "only three states!");
return BDVState(BDVState::Conflict);
case BDVState::Conflict:
return stateA;
}
llvm_unreachable("only three states!");
}
};
}
/// For a given value or instruction, figure out what base ptr it's derived
/// from. For gc objects, this is simply itself. On success, returns a value
/// which is the base pointer. (This is reliable and can be used for
/// relocation.) On failure, returns nullptr.
static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
Value *def = findBaseOrBDV(I, cache);
if (isKnownBaseResult(def)) {
return def;
}
// Here's the rough algorithm:
// - For every SSA value, construct a mapping to either an actual base
// pointer or a PHI which obscures the base pointer.
// - Construct a mapping from PHI to unknown TOP state. Use an
// optimistic algorithm to propagate base pointer information. Lattice
// looks like:
// UNKNOWN
// b1 b2 b3 b4
// CONFLICT
// When algorithm terminates, all PHIs will either have a single concrete
// base or be in a conflict state.
// - For every conflict, insert a dummy PHI node without arguments. Add
// these to the base[Instruction] = BasePtr mapping. For every
// non-conflict, add the actual base.
// - For every conflict, add arguments for the base[a] of each input
// arguments.
//
// Note: A simpler form of this would be to add the conflict form of all
// PHIs without running the optimistic algorithm. This would be
// analogous to pessimistic data flow and would likely lead to an
// overall worse solution.
#ifndef NDEBUG
auto isExpectedBDVType = [](Value *BDV) {
return isa<PHINode>(BDV) || isa<SelectInst>(BDV) ||
isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV);
};
#endif
// Once populated, will contain a mapping from each potentially non-base BDV
// to a lattice value (described above) which corresponds to that BDV.
// We use the order of insertion (DFS over the def/use graph) to provide a
// stable deterministic ordering for visiting DenseMaps (which are unordered)
// below. This is important for deterministic compilation.
MapVector<Value *, BDVState> States;
// Recursively fill in all base defining values reachable from the initial
// one for which we don't already know a definite base value for
/* scope */ {
SmallVector<Value*, 16> Worklist;
Worklist.push_back(def);
States.insert(std::make_pair(def, BDVState()));
while (!Worklist.empty()) {
Value *Current = Worklist.pop_back_val();
assert(!isKnownBaseResult(Current) && "why did it get added?");
auto visitIncomingValue = [&](Value *InVal) {
Value *Base = findBaseOrBDV(InVal, cache);
if (isKnownBaseResult(Base))
// Known bases won't need new instructions introduced and can be
// ignored safely
return;
assert(isExpectedBDVType(Base) && "the only non-base values "
"we see should be base defining values");
if (States.insert(std::make_pair(Base, BDVState())).second)
Worklist.push_back(Base);
};
if (PHINode *Phi = dyn_cast<PHINode>(Current)) {
for (Value *InVal : Phi->incoming_values())
visitIncomingValue(InVal);
} else if (SelectInst *Sel = dyn_cast<SelectInst>(Current)) {
visitIncomingValue(Sel->getTrueValue());
visitIncomingValue(Sel->getFalseValue());
} else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
visitIncomingValue(EE->getVectorOperand());
} else if (auto *IE = dyn_cast<InsertElementInst>(Current)) {
visitIncomingValue(IE->getOperand(0)); // vector operand
visitIncomingValue(IE->getOperand(1)); // scalar operand
} else {
// There is one known class of instructions we know we don't handle.
assert(isa<ShuffleVectorInst>(Current));
llvm_unreachable("unimplemented instruction case");
}
}
}
#ifndef NDEBUG
DEBUG(dbgs() << "States after initialization:\n");
for (auto Pair : States) {
DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
}
#endif
// Return a phi state for a base defining value. We'll generate a new
// base state for known bases and expect to find a cached state otherwise.
auto getStateForBDV = [&](Value *baseValue) {
if (isKnownBaseResult(baseValue))
return BDVState(baseValue);
auto I = States.find(baseValue);
assert(I != States.end() && "lookup failed!");
return I->second;
};
bool progress = true;
while (progress) {
#ifndef NDEBUG
const size_t oldSize = States.size();
#endif
progress = false;
// We're only changing values in this loop, thus safe to keep iterators.
// Since this is computing a fixed point, the order of visit does not
// effect the result. TODO: We could use a worklist here and make this run
// much faster.
for (auto Pair : States) {
Value *BDV = Pair.first;
assert(!isKnownBaseResult(BDV) && "why did it get added?");
// Given an input value for the current instruction, return a BDVState
// instance which represents the BDV of that value.
auto getStateForInput = [&](Value *V) mutable {
Value *BDV = findBaseOrBDV(V, cache);
return getStateForBDV(BDV);
};
MeetBDVStates calculateMeet;
if (SelectInst *select = dyn_cast<SelectInst>(BDV)) {
calculateMeet.meetWith(getStateForInput(select->getTrueValue()));
calculateMeet.meetWith(getStateForInput(select->getFalseValue()));
} else if (PHINode *Phi = dyn_cast<PHINode>(BDV)) {
for (Value *Val : Phi->incoming_values())
calculateMeet.meetWith(getStateForInput(Val));
} else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) {
// The 'meet' for an extractelement is slightly trivial, but it's still
// useful in that it drives us to conflict if our input is.
calculateMeet.meetWith(getStateForInput(EE->getVectorOperand()));
} else {
// Given there's a inherent type mismatch between the operands, will
// *always* produce Conflict.
auto *IE = cast<InsertElementInst>(BDV);
calculateMeet.meetWith(getStateForInput(IE->getOperand(0)));
calculateMeet.meetWith(getStateForInput(IE->getOperand(1)));
}
BDVState oldState = States[BDV];
BDVState newState = calculateMeet.getResult();
if (oldState != newState) {
progress = true;
States[BDV] = newState;
}
}
assert(oldSize == States.size() &&
"fixed point shouldn't be adding any new nodes to state");
}
#ifndef NDEBUG
DEBUG(dbgs() << "States after meet iteration:\n");
for (auto Pair : States) {
DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
}
#endif
// Insert Phis for all conflicts
// TODO: adjust naming patterns to avoid this order of iteration dependency
for (auto Pair : States) {
Instruction *I = cast<Instruction>(Pair.first);
BDVState State = Pair.second;
assert(!isKnownBaseResult(I) && "why did it get added?");
assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
// extractelement instructions are a bit special in that we may need to
// insert an extract even when we know an exact base for the instruction.
// The problem is that we need to convert from a vector base to a scalar
// base for the particular indice we're interested in.
if (State.isBase() && isa<ExtractElementInst>(I) &&
isa<VectorType>(State.getBase()->getType())) {
auto *EE = cast<ExtractElementInst>(I);
// TODO: In many cases, the new instruction is just EE itself. We should
// exploit this, but can't do it here since it would break the invariant
// about the BDV not being known to be a base.
auto *BaseInst = ExtractElementInst::Create(State.getBase(),
EE->getIndexOperand(),
"base_ee", EE);
BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
States[I] = BDVState(BDVState::Base, BaseInst);
}
// Since we're joining a vector and scalar base, they can never be the
// same. As a result, we should always see insert element having reached
// the conflict state.
if (isa<InsertElementInst>(I)) {
assert(State.isConflict());
}
if (!State.isConflict())
continue;
/// Create and insert a new instruction which will represent the base of
/// the given instruction 'I'.
auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* {
if (isa<PHINode>(I)) {
BasicBlock *BB = I->getParent();
int NumPreds = std::distance(pred_begin(BB), pred_end(BB));
assert(NumPreds > 0 && "how did we reach here");
std::string Name = suffixed_name_or(I, ".base", "base_phi");
return PHINode::Create(I->getType(), NumPreds, Name, I);
} else if (SelectInst *Sel = dyn_cast<SelectInst>(I)) {
// The undef will be replaced later
UndefValue *Undef = UndefValue::get(Sel->getType());
std::string Name = suffixed_name_or(I, ".base", "base_select");
return SelectInst::Create(Sel->getCondition(), Undef,
Undef, Name, Sel);
} else if (auto *EE = dyn_cast<ExtractElementInst>(I)) {
UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType());
std::string Name = suffixed_name_or(I, ".base", "base_ee");
return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name,
EE);
} else {
auto *IE = cast<InsertElementInst>(I);
UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType());
UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType());
std::string Name = suffixed_name_or(I, ".base", "base_ie");
return InsertElementInst::Create(VecUndef, ScalarUndef,
IE->getOperand(2), Name, IE);
}
};
Instruction *BaseInst = MakeBaseInstPlaceholder(I);
// Add metadata marking this as a base value
BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
States[I] = BDVState(BDVState::Conflict, BaseInst);
}
// Returns a instruction which produces the base pointer for a given
// instruction. The instruction is assumed to be an input to one of the BDVs
// seen in the inference algorithm above. As such, we must either already
// know it's base defining value is a base, or have inserted a new
// instruction to propagate the base of it's BDV and have entered that newly
// introduced instruction into the state table. In either case, we are
// assured to be able to determine an instruction which produces it's base
// pointer.
auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) {
Value *BDV = findBaseOrBDV(Input, cache);
Value *Base = nullptr;
if (isKnownBaseResult(BDV)) {
Base = BDV;
} else {
// Either conflict or base.
assert(States.count(BDV));
Base = States[BDV].getBase();
}
assert(Base && "can't be null");
// The cast is needed since base traversal may strip away bitcasts
if (Base->getType() != Input->getType() &&
InsertPt) {
Base = new BitCastInst(Base, Input->getType(), "cast",
InsertPt);
}
return Base;
};
// Fixup all the inputs of the new PHIs. Visit order needs to be
// deterministic and predictable because we're naming newly created
// instructions.
for (auto Pair : States) {
Instruction *BDV = cast<Instruction>(Pair.first);
BDVState State = Pair.second;
assert(!isKnownBaseResult(BDV) && "why did it get added?");
assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
if (!State.isConflict())
continue;
if (PHINode *basephi = dyn_cast<PHINode>(State.getBase())) {
PHINode *phi = cast<PHINode>(BDV);
unsigned NumPHIValues = phi->getNumIncomingValues();
for (unsigned i = 0; i < NumPHIValues; i++) {
Value *InVal = phi->getIncomingValue(i);
BasicBlock *InBB = phi->getIncomingBlock(i);
// If we've already seen InBB, add the same incoming value
// we added for it earlier. The IR verifier requires phi
// nodes with multiple entries from the same basic block
// to have the same incoming value for each of those
// entries. If we don't do this check here and basephi
// has a different type than base, we'll end up adding two
// bitcasts (and hence two distinct values) as incoming
// values for the same basic block.
int blockIndex = basephi->getBasicBlockIndex(InBB);
if (blockIndex != -1) {
Value *oldBase = basephi->getIncomingValue(blockIndex);
basephi->addIncoming(oldBase, InBB);
#ifndef NDEBUG
Value *Base = getBaseForInput(InVal, nullptr);
// In essence this assert states: the only way two
// values incoming from the same basic block may be
// different is by being different bitcasts of the same
// value. A cleanup that remains TODO is changing
// findBaseOrBDV to return an llvm::Value of the correct
// type (and still remain pure). This will remove the
// need to add bitcasts.
assert(Base->stripPointerCasts() == oldBase->stripPointerCasts() &&
"sanity -- findBaseOrBDV should be pure!");
#endif
continue;
}
// Find the instruction which produces the base for each input. We may
// need to insert a bitcast in the incoming block.
// TODO: Need to split critical edges if insertion is needed
Value *Base = getBaseForInput(InVal, InBB->getTerminator());
basephi->addIncoming(Base, InBB);
}
assert(basephi->getNumIncomingValues() == NumPHIValues);
} else if (SelectInst *BaseSel = dyn_cast<SelectInst>(State.getBase())) {
SelectInst *Sel = cast<SelectInst>(BDV);
// Operand 1 & 2 are true, false path respectively. TODO: refactor to
// something more safe and less hacky.
for (int i = 1; i <= 2; i++) {
Value *InVal = Sel->getOperand(i);
// Find the instruction which produces the base for each input. We may
// need to insert a bitcast.
Value *Base = getBaseForInput(InVal, BaseSel);
BaseSel->setOperand(i, Base);
}
} else if (auto *BaseEE = dyn_cast<ExtractElementInst>(State.getBase())) {
Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand();
// Find the instruction which produces the base for each input. We may
// need to insert a bitcast.
Value *Base = getBaseForInput(InVal, BaseEE);
BaseEE->setOperand(0, Base);
} else {
auto *BaseIE = cast<InsertElementInst>(State.getBase());
auto *BdvIE = cast<InsertElementInst>(BDV);
auto UpdateOperand = [&](int OperandIdx) {
Value *InVal = BdvIE->getOperand(OperandIdx);
Value *Base = getBaseForInput(InVal, BaseIE);
BaseIE->setOperand(OperandIdx, Base);
};
UpdateOperand(0); // vector operand
UpdateOperand(1); // scalar operand
}
}
// Now that we're done with the algorithm, see if we can optimize the
// results slightly by reducing the number of new instructions needed.
// Arguably, this should be integrated into the algorithm above, but
// doing as a post process step is easier to reason about for the moment.
DenseMap<Value *, Value *> ReverseMap;
SmallPtrSet<Instruction *, 16> NewInsts;
SmallSetVector<AssertingVH<Instruction>, 16> Worklist;
// Note: We need to visit the states in a deterministic order. We uses the
// Keys we sorted above for this purpose. Note that we are papering over a
// bigger problem with the algorithm above - it's visit order is not
// deterministic. A larger change is needed to fix this.
for (auto Pair : States) {
auto *BDV = Pair.first;
auto State = Pair.second;
Value *Base = State.getBase();
assert(BDV && Base);
assert(!isKnownBaseResult(BDV) && "why did it get added?");
assert(isKnownBaseResult(Base) &&
"must be something we 'know' is a base pointer");
if (!State.isConflict())
continue;
ReverseMap[Base] = BDV;
if (auto *BaseI = dyn_cast<Instruction>(Base)) {
NewInsts.insert(BaseI);
Worklist.insert(BaseI);
}
}
auto ReplaceBaseInstWith = [&](Value *BDV, Instruction *BaseI,
Value *Replacement) {
// Add users which are new instructions (excluding self references)
for (User *U : BaseI->users())
if (auto *UI = dyn_cast<Instruction>(U))
if (NewInsts.count(UI) && UI != BaseI)
Worklist.insert(UI);
// Then do the actual replacement
NewInsts.erase(BaseI);
ReverseMap.erase(BaseI);
BaseI->replaceAllUsesWith(Replacement);
assert(States.count(BDV));
assert(States[BDV].isConflict() && States[BDV].getBase() == BaseI);
States[BDV] = BDVState(BDVState::Conflict, Replacement);
BaseI->eraseFromParent();
};
const DataLayout &DL = cast<Instruction>(def)->getModule()->getDataLayout();
while (!Worklist.empty()) {
Instruction *BaseI = Worklist.pop_back_val();
assert(NewInsts.count(BaseI));
Value *Bdv = ReverseMap[BaseI];
if (auto *BdvI = dyn_cast<Instruction>(Bdv))
if (BaseI->isIdenticalTo(BdvI)) {
DEBUG(dbgs() << "Identical Base: " << *BaseI << "\n");
ReplaceBaseInstWith(Bdv, BaseI, Bdv);
continue;
}
if (Value *V = SimplifyInstruction(BaseI, DL)) {
DEBUG(dbgs() << "Base " << *BaseI << " simplified to " << *V << "\n");
ReplaceBaseInstWith(Bdv, BaseI, V);
continue;
}
}
// Cache all of our results so we can cheaply reuse them
// NOTE: This is actually two caches: one of the base defining value
// relation and one of the base pointer relation! FIXME
for (auto Pair : States) {
auto *BDV = Pair.first;
Value *base = Pair.second.getBase();
assert(BDV && base);
std::string fromstr = cache.count(BDV) ? cache[BDV]->getName() : "none";
DEBUG(dbgs() << "Updating base value cache"
<< " for: " << BDV->getName()
<< " from: " << fromstr
<< " to: " << base->getName() << "\n");
if (cache.count(BDV)) {
// Once we transition from the BDV relation being store in the cache to
// the base relation being stored, it must be stable
assert((!isKnownBaseResult(cache[BDV]) || cache[BDV] == base) &&
"base relation should be stable");
}
cache[BDV] = base;
}
assert(cache.count(def));
return cache[def];
}
// For a set of live pointers (base and/or derived), identify the base
// pointer of the object which they are derived from. This routine will
// mutate the IR graph as needed to make the 'base' pointer live at the
// definition site of 'derived'. This ensures that any use of 'derived' can
// also use 'base'. This may involve the insertion of a number of
// additional PHI nodes.
//
// preconditions: live is a set of pointer type Values
//
// side effects: may insert PHI nodes into the existing CFG, will preserve
// CFG, will not remove or mutate any existing nodes
//
// post condition: PointerToBase contains one (derived, base) pair for every
// pointer in live. Note that derived can be equal to base if the original
// pointer was a base pointer.
static void
findBasePointers(const StatepointLiveSetTy &live,
DenseMap<Value *, Value *> &PointerToBase,
DominatorTree *DT, DefiningValueMapTy &DVCache) {
// For the naming of values inserted to be deterministic - which makes for
// much cleaner and more stable tests - we need to assign an order to the
// live values. DenseSets do not provide a deterministic order across runs.
SmallVector<Value *, 64> Temp;
Temp.insert(Temp.end(), live.begin(), live.end());
std::sort(Temp.begin(), Temp.end(), order_by_name);
for (Value *ptr : Temp) {
Value *base = findBasePointer(ptr, DVCache);
assert(base && "failed to find base pointer");
PointerToBase[ptr] = base;
assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) ||
DT->dominates(cast<Instruction>(base)->getParent(),
cast<Instruction>(ptr)->getParent())) &&
"The base we found better dominate the derived pointer");
// If you see this trip and like to live really dangerously, the code should
// be correct, just with idioms the verifier can't handle. You can try
// disabling the verifier at your own substantial risk.
assert(!isa<ConstantPointerNull>(base) &&
"the relocation code needs adjustment to handle the relocation of "
"a null pointer constant without causing false positives in the "
"safepoint ir verifier.");
}
}
/// Find the required based pointers (and adjust the live set) for the given
/// parse point.
static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache,
const CallSite &CS,
PartiallyConstructedSafepointRecord &result) {
DenseMap<Value *, Value *> PointerToBase;
findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache);
if (PrintBasePointers) {
// Note: Need to print these in a stable order since this is checked in
// some tests.
errs() << "Base Pairs (w/o Relocation):\n";
SmallVector<Value *, 64> Temp;
Temp.reserve(PointerToBase.size());
for (auto Pair : PointerToBase) {
Temp.push_back(Pair.first);
}
std::sort(Temp.begin(), Temp.end(), order_by_name);
for (Value *Ptr : Temp) {
Value *Base = PointerToBase[Ptr];
errs() << " derived ";
Ptr->printAsOperand(errs(), false);
errs() << " base ";
Base->printAsOperand(errs(), false);
errs() << "\n";;
}
}
result.PointerToBase = PointerToBase;
}
/// Given an updated version of the dataflow liveness results, update the
/// liveset and base pointer maps for the call site CS.
static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
const CallSite &CS,
PartiallyConstructedSafepointRecord &result);
static void recomputeLiveInValues(
Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
// TODO-PERF: reuse the original liveness, then simply run the dataflow
// again. The old values are still live and will help it stabilize quickly.
GCPtrLivenessData RevisedLivenessData;
computeLiveInValues(DT, F, RevisedLivenessData);
for (size_t i = 0; i < records.size(); i++) {
struct PartiallyConstructedSafepointRecord &info = records[i];
const CallSite &CS = toUpdate[i];
recomputeLiveInValues(RevisedLivenessData, CS, info);
}
}
// When inserting gc.relocate and gc.result calls, we need to ensure there are
// no uses of the original value / return value between the gc.statepoint and
// the gc.relocate / gc.result call. One case which can arise is a phi node
// starting one of the successor blocks. We also need to be able to insert the
// gc.relocates only on the path which goes through the statepoint. We might
// need to split an edge to make this possible.
static BasicBlock *
normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent,
DominatorTree &DT) {
BasicBlock *Ret = BB;
if (!BB->getUniquePredecessor())
Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT);
// Now that 'Ret' has unique predecessor we can safely remove all phi nodes
// from it
FoldSingleEntryPHINodes(Ret);
assert(!isa<PHINode>(Ret->begin()) &&
"All PHI nodes should have been removed!");
// At this point, we can safely insert a gc.relocate or gc.result as the first
// instruction in Ret if needed.
return Ret;
}
// Create new attribute set containing only attributes which can be transferred
// from original call to the safepoint.
static AttributeSet legalizeCallAttributes(AttributeSet AS) {
AttributeSet Ret;
for (unsigned Slot = 0; Slot < AS.getNumSlots(); Slot++) {
unsigned Index = AS.getSlotIndex(Slot);
if (Index == AttributeSet::ReturnIndex ||
Index == AttributeSet::FunctionIndex) {
for (Attribute Attr : make_range(AS.begin(Slot), AS.end(Slot))) {
// Do not allow certain attributes - just skip them
// Safepoint can not be read only or read none.
if (Attr.hasAttribute(Attribute::ReadNone) ||
Attr.hasAttribute(Attribute::ReadOnly))
continue;
// These attributes control the generation of the gc.statepoint call /
// invoke itself; and once the gc.statepoint is in place, they're of no
// use.
if (Attr.hasAttribute("statepoint-num-patch-bytes") ||
Attr.hasAttribute("statepoint-id"))
continue;
Ret = Ret.addAttributes(
AS.getContext(), Index,
AttributeSet::get(AS.getContext(), Index, AttrBuilder(Attr)));
}
}
// Just skip parameter attributes for now
}
return Ret;
}
/// Helper function to place all gc relocates necessary for the given
/// statepoint.
/// Inputs:
/// liveVariables - list of variables to be relocated.
/// liveStart - index of the first live variable.
/// basePtrs - base pointers.
/// statepointToken - statepoint instruction to which relocates should be
/// bound.
/// Builder - Llvm IR builder to be used to construct new calls.
static void CreateGCRelocates(ArrayRef<Value *> LiveVariables,
const int LiveStart,
ArrayRef<Value *> BasePtrs,
Instruction *StatepointToken,
IRBuilder<> Builder) {
if (LiveVariables.empty())
return;
auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) {
auto ValIt = std::find(LiveVec.begin(), LiveVec.end(), Val);
assert(ValIt != LiveVec.end() && "Val not found in LiveVec!");
size_t Index = std::distance(LiveVec.begin(), ValIt);
assert(Index < LiveVec.size() && "Bug in std::find?");
return Index;
};
Module *M = StatepointToken->getModule();
// All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose
// element type is i8 addrspace(1)*). We originally generated unique
// declarations for each pointer type, but this proved problematic because
// the intrinsic mangling code is incomplete and fragile. Since we're moving
// towards a single unified pointer type anyways, we can just cast everything
// to an i8* of the right address space. A bitcast is added later to convert
// gc_relocate to the actual value's type.
auto getGCRelocateDecl = [&] (Type *Ty) {
assert(isHandledGCPointerType(Ty));
auto AS = Ty->getScalarType()->getPointerAddressSpace();
Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS);
if (auto *VT = dyn_cast<VectorType>(Ty))
NewTy = VectorType::get(NewTy, VT->getNumElements());
return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate,
{NewTy});
};
// Lazily populated map from input types to the canonicalized form mentioned
// in the comment above. This should probably be cached somewhere more
// broadly.
DenseMap<Type*, Value*> TypeToDeclMap;
for (unsigned i = 0; i < LiveVariables.size(); i++) {
// Generate the gc.relocate call and save the result
Value *BaseIdx =
Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i]));
Value *LiveIdx = Builder.getInt32(LiveStart + i);
Type *Ty = LiveVariables[i]->getType();
if (!TypeToDeclMap.count(Ty))
TypeToDeclMap[Ty] = getGCRelocateDecl(Ty);
Value *GCRelocateDecl = TypeToDeclMap[Ty];
// only specify a debug name if we can give a useful one
CallInst *Reloc = Builder.CreateCall(
GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx},
suffixed_name_or(LiveVariables[i], ".relocated", ""));
// Trick CodeGen into thinking there are lots of free registers at this
// fake call.
Reloc->setCallingConv(CallingConv::Cold);
}
}
namespace {
/// This struct is used to defer RAUWs and `eraseFromParent` s. Using this
/// avoids having to worry about keeping around dangling pointers to Values.
class DeferredReplacement {
AssertingVH<Instruction> Old;
AssertingVH<Instruction> New;
public:
explicit DeferredReplacement(Instruction *Old, Instruction *New) :
Old(Old), New(New) {
assert(Old != New && "Not allowed!");
}
/// Does the task represented by this instance.
void doReplacement() {
Instruction *OldI = Old;
Instruction *NewI = New;
assert(OldI != NewI && "Disallowed at construction?!");
Old = nullptr;
New = nullptr;
if (NewI)
OldI->replaceAllUsesWith(NewI);
OldI->eraseFromParent();
}
};
}
static void
makeStatepointExplicitImpl(const CallSite CS, /* to replace */
const SmallVectorImpl<Value *> &BasePtrs,
const SmallVectorImpl<Value *> &LiveVariables,
PartiallyConstructedSafepointRecord &Result,
std::vector<DeferredReplacement> &Replacements) {
assert(BasePtrs.size() == LiveVariables.size());
assert((UseDeoptBundles || isStatepoint(CS)) &&
"This method expects to be rewriting a statepoint");
// Then go ahead and use the builder do actually do the inserts. We insert
// immediately before the previous instruction under the assumption that all
// arguments will be available here. We can't insert afterwards since we may
// be replacing a terminator.
Instruction *InsertBefore = CS.getInstruction();
IRBuilder<> Builder(InsertBefore);
ArrayRef<Value *> GCArgs(LiveVariables);
uint64_t StatepointID = 0xABCDEF00;
uint32_t NumPatchBytes = 0;
uint32_t Flags = uint32_t(StatepointFlags::None);
ArrayRef<Use> CallArgs;
ArrayRef<Use> DeoptArgs;
ArrayRef<Use> TransitionArgs;
Value *CallTarget = nullptr;
if (UseDeoptBundles) {
CallArgs = {CS.arg_begin(), CS.arg_end()};
DeoptArgs = GetDeoptBundleOperands(CS);
if (auto TransitionBundle =
CS.getOperandBundle(LLVMContext::OB_gc_transition)) {
Flags |= uint32_t(StatepointFlags::GCTransition);
TransitionArgs = TransitionBundle->Inputs;
}
AttributeSet OriginalAttrs = CS.getAttributes();
Attribute AttrID = OriginalAttrs.getAttribute(AttributeSet::FunctionIndex,
"statepoint-id");
if (AttrID.isStringAttribute())
AttrID.getValueAsString().getAsInteger(10, StatepointID);
Attribute AttrNumPatchBytes = OriginalAttrs.getAttribute(
AttributeSet::FunctionIndex, "statepoint-num-patch-bytes");
if (AttrNumPatchBytes.isStringAttribute())
AttrNumPatchBytes.getValueAsString().getAsInteger(10, NumPatchBytes);
CallTarget = CS.getCalledValue();
} else {
// This branch will be gone soon, and we will soon only support the
// UseDeoptBundles == true configuration.
Statepoint OldSP(CS);
StatepointID = OldSP.getID();
NumPatchBytes = OldSP.getNumPatchBytes();
Flags = OldSP.getFlags();
CallArgs = {OldSP.arg_begin(), OldSP.arg_end()};
DeoptArgs = {OldSP.vm_state_begin(), OldSP.vm_state_end()};
TransitionArgs = {OldSP.gc_transition_args_begin(),
OldSP.gc_transition_args_end()};
CallTarget = OldSP.getCalledValue();
}
// Create the statepoint given all the arguments
Instruction *Token = nullptr;
AttributeSet ReturnAttrs;
if (CS.isCall()) {
CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
CallInst *Call = Builder.CreateGCStatepointCall(
StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs,
TransitionArgs, DeoptArgs, GCArgs, "safepoint_token");
Call->setTailCall(ToReplace->isTailCall());
Call->setCallingConv(ToReplace->getCallingConv());
// Currently we will fail on parameter attributes and on certain
// function attributes.
AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes());
// In case if we can handle this set of attributes - set up function attrs
// directly on statepoint and return attrs later for gc_result intrinsic.
Call->setAttributes(NewAttrs.getFnAttributes());
ReturnAttrs = NewAttrs.getRetAttributes();
Token = Call;
// Put the following gc_result and gc_relocate calls immediately after the
// the old call (which we're about to delete)
assert(ToReplace->getNextNode() && "Not a terminator, must have next!");
Builder.SetInsertPoint(ToReplace->getNextNode());
Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc());
} else {
InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction());
// Insert the new invoke into the old block. We'll remove the old one in a
// moment at which point this will become the new terminator for the
// original block.
InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(),
ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs,
GCArgs, "statepoint_token");
Invoke->setCallingConv(ToReplace->getCallingConv());
// Currently we will fail on parameter attributes and on certain
// function attributes.
AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes());
// In case if we can handle this set of attributes - set up function attrs
// directly on statepoint and return attrs later for gc_result intrinsic.
Invoke->setAttributes(NewAttrs.getFnAttributes());
ReturnAttrs = NewAttrs.getRetAttributes();
Token = Invoke;
// Generate gc relocates in exceptional path
BasicBlock *UnwindBlock = ToReplace->getUnwindDest();
assert(!isa<PHINode>(UnwindBlock->begin()) &&
UnwindBlock->getUniquePredecessor() &&
"can't safely insert in this block!");
Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt());
Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc());
// Attach exceptional gc relocates to the landingpad.
Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst();
Result.UnwindToken = ExceptionalToken;
const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken,
Builder);
// Generate gc relocates and returns for normal block
BasicBlock *NormalDest = ToReplace->getNormalDest();
assert(!isa<PHINode>(NormalDest->begin()) &&
NormalDest->getUniquePredecessor() &&
"can't safely insert in this block!");
Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt());
// gc relocates will be generated later as if it were regular call
// statepoint
}
assert(Token && "Should be set in one of the above branches!");
if (UseDeoptBundles) {
Token->setName("statepoint_token");
if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) {
StringRef Name =
CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : "";
CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name);
GCResult->setAttributes(CS.getAttributes().getRetAttributes());
// We cannot RAUW or delete CS.getInstruction() because it could be in the
// live set of some other safepoint, in which case that safepoint's
// PartiallyConstructedSafepointRecord will hold a raw pointer to this
// llvm::Instruction. Instead, we defer the replacement and deletion to
// after the live sets have been made explicit in the IR, and we no longer
// have raw pointers to worry about.
Replacements.emplace_back(CS.getInstruction(), GCResult);
} else {
Replacements.emplace_back(CS.getInstruction(), nullptr);
}
} else {
assert(!CS.getInstruction()->hasNUsesOrMore(2) &&
"only valid use before rewrite is gc.result");
assert(!CS.getInstruction()->hasOneUse() ||
isGCResult(cast<Instruction>(*CS.getInstruction()->user_begin())));
// Take the name of the original statepoint token if there was one.
Token->takeName(CS.getInstruction());
// Update the gc.result of the original statepoint (if any) to use the newly
// inserted statepoint. This is safe to do here since the token can't be
// considered a live reference.
CS.getInstruction()->replaceAllUsesWith(Token);
CS.getInstruction()->eraseFromParent();
}
Result.StatepointToken = Token;
// Second, create a gc.relocate for every live variable
const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder);
}
namespace {
struct NameOrdering {
Value *Base;
Value *Derived;
bool operator()(NameOrdering const &a, NameOrdering const &b) {
return -1 == a.Derived->getName().compare(b.Derived->getName());
}
};
}
static void StabilizeOrder(SmallVectorImpl<Value *> &BaseVec,
SmallVectorImpl<Value *> &LiveVec) {
assert(BaseVec.size() == LiveVec.size());
SmallVector<NameOrdering, 64> Temp;
for (size_t i = 0; i < BaseVec.size(); i++) {
NameOrdering v;
v.Base = BaseVec[i];
v.Derived = LiveVec[i];
Temp.push_back(v);
}
std::sort(Temp.begin(), Temp.end(), NameOrdering());
for (size_t i = 0; i < BaseVec.size(); i++) {
BaseVec[i] = Temp[i].Base;
LiveVec[i] = Temp[i].Derived;
}
}
// Replace an existing gc.statepoint with a new one and a set of gc.relocates
// which make the relocations happening at this safepoint explicit.
//
// WARNING: Does not do any fixup to adjust users of the original live
// values. That's the callers responsibility.
static void
makeStatepointExplicit(DominatorTree &DT, const CallSite &CS,
PartiallyConstructedSafepointRecord &Result,
std::vector<DeferredReplacement> &Replacements) {
const auto &LiveSet = Result.LiveSet;
const auto &PointerToBase = Result.PointerToBase;
// Convert to vector for efficient cross referencing.
SmallVector<Value *, 64> BaseVec, LiveVec;
LiveVec.reserve(LiveSet.size());
BaseVec.reserve(LiveSet.size());
for (Value *L : LiveSet) {
LiveVec.push_back(L);
assert(PointerToBase.count(L));
Value *Base = PointerToBase.find(L)->second;
BaseVec.push_back(Base);
}
assert(LiveVec.size() == BaseVec.size());
// To make the output IR slightly more stable (for use in diffs), ensure a
// fixed order of the values in the safepoint (by sorting the value name).
// The order is otherwise meaningless.
StabilizeOrder(BaseVec, LiveVec);
// Do the actual rewriting and delete the old statepoint
makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements);
}
// Helper function for the relocationViaAlloca.
//
// It receives iterator to the statepoint gc relocates and emits a store to the
// assigned location (via allocaMap) for the each one of them. It adds the
// visited values into the visitedLiveValues set, which we will later use them
// for sanity checking.
static void
insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs,
DenseMap<Value *, Value *> &AllocaMap,
DenseSet<Value *> &VisitedLiveValues) {
for (User *U : GCRelocs) {
GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U);
if (!Relocate)
continue;
Value *OriginalValue = const_cast<Value *>(Relocate->getDerivedPtr());
assert(AllocaMap.count(OriginalValue));
Value *Alloca = AllocaMap[OriginalValue];
// Emit store into the related alloca
// All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to
// the correct type according to alloca.
assert(Relocate->getNextNode() &&
"Should always have one since it's not a terminator");
IRBuilder<> Builder(Relocate->getNextNode());
Value *CastedRelocatedValue =
Builder.CreateBitCast(Relocate,
cast<AllocaInst>(Alloca)->getAllocatedType(),
suffixed_name_or(Relocate, ".casted", ""));
StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca);
Store->insertAfter(cast<Instruction>(CastedRelocatedValue));
#ifndef NDEBUG
VisitedLiveValues.insert(OriginalValue);
#endif
}
}
// Helper function for the "relocationViaAlloca". Similar to the
// "insertRelocationStores" but works for rematerialized values.
static void
insertRematerializationStores(
RematerializedValueMapTy RematerializedValues,
DenseMap<Value *, Value *> &AllocaMap,
DenseSet<Value *> &VisitedLiveValues) {
for (auto RematerializedValuePair: RematerializedValues) {
Instruction *RematerializedValue = RematerializedValuePair.first;
Value *OriginalValue = RematerializedValuePair.second;
assert(AllocaMap.count(OriginalValue) &&
"Can not find alloca for rematerialized value");
Value *Alloca = AllocaMap[OriginalValue];
StoreInst *Store = new StoreInst(RematerializedValue, Alloca);
Store->insertAfter(RematerializedValue);
#ifndef NDEBUG
VisitedLiveValues.insert(OriginalValue);
#endif
}
}
/// Do all the relocation update via allocas and mem2reg
static void relocationViaAlloca(
Function &F, DominatorTree &DT, ArrayRef<Value *> Live,
ArrayRef<PartiallyConstructedSafepointRecord> Records) {
#ifndef NDEBUG
// record initial number of (static) allocas; we'll check we have the same
// number when we get done.
int InitialAllocaNum = 0;
for (auto I = F.getEntryBlock().begin(), E = F.getEntryBlock().end(); I != E;
I++)
if (isa<AllocaInst>(*I))
InitialAllocaNum++;
#endif
// TODO-PERF: change data structures, reserve
DenseMap<Value *, Value *> AllocaMap;
SmallVector<AllocaInst *, 200> PromotableAllocas;
// Used later to chack that we have enough allocas to store all values
std::size_t NumRematerializedValues = 0;
PromotableAllocas.reserve(Live.size());
// Emit alloca for "LiveValue" and record it in "allocaMap" and
// "PromotableAllocas"
auto emitAllocaFor = [&](Value *LiveValue) {
AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), "",
F.getEntryBlock().getFirstNonPHI());
AllocaMap[LiveValue] = Alloca;
PromotableAllocas.push_back(Alloca);
};
// Emit alloca for each live gc pointer
for (Value *V : Live)
emitAllocaFor(V);
// Emit allocas for rematerialized values
for (const auto &Info : Records)
for (auto RematerializedValuePair : Info.RematerializedValues) {
Value *OriginalValue = RematerializedValuePair.second;
if (AllocaMap.count(OriginalValue) != 0)
continue;
emitAllocaFor(OriginalValue);
++NumRematerializedValues;
}
// The next two loops are part of the same conceptual operation. We need to
// insert a store to the alloca after the original def and at each
// redefinition. We need to insert a load before each use. These are split
// into distinct loops for performance reasons.
// Update gc pointer after each statepoint: either store a relocated value or
// null (if no relocated value was found for this gc pointer and it is not a
// gc_result). This must happen before we update the statepoint with load of
// alloca otherwise we lose the link between statepoint and old def.
for (const auto &Info : Records) {
Value *Statepoint = Info.StatepointToken;
// This will be used for consistency check
DenseSet<Value *> VisitedLiveValues;
// Insert stores for normal statepoint gc relocates
insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues);
// In case if it was invoke statepoint
// we will insert stores for exceptional path gc relocates.
if (isa<InvokeInst>(Statepoint)) {
insertRelocationStores(Info.UnwindToken->users(), AllocaMap,
VisitedLiveValues);
}
// Do similar thing with rematerialized values
insertRematerializationStores(Info.RematerializedValues, AllocaMap,
VisitedLiveValues);
if (ClobberNonLive) {
// As a debugging aid, pretend that an unrelocated pointer becomes null at
// the gc.statepoint. This will turn some subtle GC problems into
// slightly easier to debug SEGVs. Note that on large IR files with
// lots of gc.statepoints this is extremely costly both memory and time
// wise.
SmallVector<AllocaInst *, 64> ToClobber;
for (auto Pair : AllocaMap) {
Value *Def = Pair.first;
AllocaInst *Alloca = cast<AllocaInst>(Pair.second);
// This value was relocated
if (VisitedLiveValues.count(Def)) {
continue;
}
ToClobber.push_back(Alloca);
}
auto InsertClobbersAt = [&](Instruction *IP) {
for (auto *AI : ToClobber) {
auto PT = cast<PointerType>(AI->getAllocatedType());
Constant *CPN = ConstantPointerNull::get(PT);
StoreInst *Store = new StoreInst(CPN, AI);
Store->insertBefore(IP);
}
};
// Insert the clobbering stores. These may get intermixed with the
// gc.results and gc.relocates, but that's fine.
if (auto II = dyn_cast<InvokeInst>(Statepoint)) {
InsertClobbersAt(&*II->getNormalDest()->getFirstInsertionPt());
InsertClobbersAt(&*II->getUnwindDest()->getFirstInsertionPt());
} else {
InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode());
}
}
}
// Update use with load allocas and add store for gc_relocated.
for (auto Pair : AllocaMap) {
Value *Def = Pair.first;
Value *Alloca = Pair.second;
// We pre-record the uses of allocas so that we dont have to worry about
// later update that changes the user information..
SmallVector<Instruction *, 20> Uses;
// PERF: trade a linear scan for repeated reallocation
Uses.reserve(std::distance(Def->user_begin(), Def->user_end()));
for (User *U : Def->users()) {
if (!isa<ConstantExpr>(U)) {
// If the def has a ConstantExpr use, then the def is either a
// ConstantExpr use itself or null. In either case
// (recursively in the first, directly in the second), the oop
// it is ultimately dependent on is null and this particular
// use does not need to be fixed up.
Uses.push_back(cast<Instruction>(U));
}
}
std::sort(Uses.begin(), Uses.end());
auto Last = std::unique(Uses.begin(), Uses.end());
Uses.erase(Last, Uses.end());
for (Instruction *Use : Uses) {
if (isa<PHINode>(Use)) {
PHINode *Phi = cast<PHINode>(Use);
for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) {
if (Def == Phi->getIncomingValue(i)) {
LoadInst *Load = new LoadInst(
Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
Phi->setIncomingValue(i, Load);
}
}
} else {
LoadInst *Load = new LoadInst(Alloca, "", Use);
Use->replaceUsesOfWith(Def, Load);
}
}
// Emit store for the initial gc value. Store must be inserted after load,
// otherwise store will be in alloca's use list and an extra load will be
// inserted before it.
StoreInst *Store = new StoreInst(Def, Alloca);
if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
// InvokeInst is a TerminatorInst so the store need to be inserted
// into its normal destination block.
BasicBlock *NormalDest = Invoke->getNormalDest();
Store->insertBefore(NormalDest->getFirstNonPHI());
} else {
assert(!Inst->isTerminator() &&
"The only TerminatorInst that can produce a value is "
"InvokeInst which is handled above.");
Store->insertAfter(Inst);
}
} else {
assert(isa<Argument>(Def));
Store->insertAfter(cast<Instruction>(Alloca));
}
}
assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
"we must have the same allocas with lives");
if (!PromotableAllocas.empty()) {
// Apply mem2reg to promote alloca to SSA
PromoteMemToReg(PromotableAllocas, DT);
}
#ifndef NDEBUG
for (auto &I : F.getEntryBlock())
if (isa<AllocaInst>(I))
InitialAllocaNum--;
assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas");
#endif
}
/// Implement a unique function which doesn't require we sort the input
/// vector. Doing so has the effect of changing the output of a couple of
/// tests in ways which make them less useful in testing fused safepoints.
template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) {
SmallSet<T, 8> Seen;
Vec.erase(std::remove_if(Vec.begin(), Vec.end(), [&](const T &V) {
return !Seen.insert(V).second;
}), Vec.end());
}
/// Insert holders so that each Value is obviously live through the entire
/// lifetime of the call.
static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values,
SmallVectorImpl<CallInst *> &Holders) {
if (Values.empty())
// No values to hold live, might as well not insert the empty holder
return;
Module *M = CS.getInstruction()->getModule();
// Use a dummy vararg function to actually hold the values live
Function *Func = cast<Function>(M->getOrInsertFunction(
"__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)));
if (CS.isCall()) {
// For call safepoints insert dummy calls right after safepoint
Holders.push_back(CallInst::Create(Func, Values, "",
&*++CS.getInstruction()->getIterator()));
return;
}
// For invoke safepooints insert dummy calls both in normal and
// exceptional destination blocks
auto *II = cast<InvokeInst>(CS.getInstruction());
Holders.push_back(CallInst::Create(
Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt()));
Holders.push_back(CallInst::Create(
Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt()));
}
static void findLiveReferences(
Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
GCPtrLivenessData OriginalLivenessData;
computeLiveInValues(DT, F, OriginalLivenessData);
for (size_t i = 0; i < records.size(); i++) {
struct PartiallyConstructedSafepointRecord &info = records[i];
const CallSite &CS = toUpdate[i];
analyzeParsePointLiveness(DT, OriginalLivenessData, CS, info);
}
}
/// Remove any vector of pointers from the live set by scalarizing them over the
/// statepoint instruction. Adds the scalarized pieces to the live set. It
/// would be preferable to include the vector in the statepoint itself, but
/// the lowering code currently does not handle that. Extending it would be
/// slightly non-trivial since it requires a format change. Given how rare
/// such cases are (for the moment?) scalarizing is an acceptable compromise.
static void splitVectorValues(Instruction *StatepointInst,
StatepointLiveSetTy &LiveSet,
DenseMap<Value *, Value *>& PointerToBase,
DominatorTree &DT) {
SmallVector<Value *, 16> ToSplit;
for (Value *V : LiveSet)
if (isa<VectorType>(V->getType()))
ToSplit.push_back(V);
if (ToSplit.empty())
return;
DenseMap<Value *, SmallVector<Value *, 16>> ElementMapping;
Function &F = *(StatepointInst->getParent()->getParent());
DenseMap<Value *, AllocaInst *> AllocaMap;
// First is normal return, second is exceptional return (invoke only)
DenseMap<Value *, std::pair<Value *, Value *>> Replacements;
for (Value *V : ToSplit) {
AllocaInst *Alloca =
new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI());
AllocaMap[V] = Alloca;
VectorType *VT = cast<VectorType>(V->getType());
IRBuilder<> Builder(StatepointInst);
SmallVector<Value *, 16> Elements;
for (unsigned i = 0; i < VT->getNumElements(); i++)
Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i)));
ElementMapping[V] = Elements;
auto InsertVectorReform = [&](Instruction *IP) {
Builder.SetInsertPoint(IP);
Builder.SetCurrentDebugLocation(IP->getDebugLoc());
Value *ResultVec = UndefValue::get(VT);
for (unsigned i = 0; i < VT->getNumElements(); i++)
ResultVec = Builder.CreateInsertElement(ResultVec, Elements[i],
Builder.getInt32(i));
return ResultVec;
};
if (isa<CallInst>(StatepointInst)) {
BasicBlock::iterator Next(StatepointInst);
Next++;
Instruction *IP = &*(Next);
Replacements[V].first = InsertVectorReform(IP);
Replacements[V].second = nullptr;
} else {
InvokeInst *Invoke = cast<InvokeInst>(StatepointInst);
// We've already normalized - check that we don't have shared destination
// blocks
BasicBlock *NormalDest = Invoke->getNormalDest();
assert(!isa<PHINode>(NormalDest->begin()));
BasicBlock *UnwindDest = Invoke->getUnwindDest();
assert(!isa<PHINode>(UnwindDest->begin()));
// Insert insert element sequences in both successors
Instruction *IP = &*(NormalDest->getFirstInsertionPt());
Replacements[V].first = InsertVectorReform(IP);
IP = &*(UnwindDest->getFirstInsertionPt());
Replacements[V].second = InsertVectorReform(IP);
}
}
for (Value *V : ToSplit) {
AllocaInst *Alloca = AllocaMap[V];
// Capture all users before we start mutating use lists
SmallVector<Instruction *, 16> Users;
for (User *U : V->users())
Users.push_back(cast<Instruction>(U));
for (Instruction *I : Users) {
if (auto Phi = dyn_cast<PHINode>(I)) {
for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++)
if (V == Phi->getIncomingValue(i)) {
LoadInst *Load = new LoadInst(
Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
Phi->setIncomingValue(i, Load);
}
} else {
LoadInst *Load = new LoadInst(Alloca, "", I);
I->replaceUsesOfWith(V, Load);
}
}
// Store the original value and the replacement value into the alloca
StoreInst *Store = new StoreInst(V, Alloca);
if (auto I = dyn_cast<Instruction>(V))
Store->insertAfter(I);
else
Store->insertAfter(Alloca);
// Normal return for invoke, or call return
Instruction *Replacement = cast<Instruction>(Replacements[V].first);
(new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
// Unwind return for invoke only
Replacement = cast_or_null<Instruction>(Replacements[V].second);
if (Replacement)
(new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
}
// apply mem2reg to promote alloca to SSA
SmallVector<AllocaInst *, 16> Allocas;
for (Value *V : ToSplit)
Allocas.push_back(AllocaMap[V]);
PromoteMemToReg(Allocas, DT);
// Update our tracking of live pointers and base mappings to account for the
// changes we just made.
for (Value *V : ToSplit) {
auto &Elements = ElementMapping[V];
LiveSet.erase(V);
LiveSet.insert(Elements.begin(), Elements.end());
// We need to update the base mapping as well.
assert(PointerToBase.count(V));
Value *OldBase = PointerToBase[V];
auto &BaseElements = ElementMapping[OldBase];
PointerToBase.erase(V);
assert(Elements.size() == BaseElements.size());
for (unsigned i = 0; i < Elements.size(); i++) {
Value *Elem = Elements[i];
PointerToBase[Elem] = BaseElements[i];
}
}
}
// Helper function for the "rematerializeLiveValues". It walks use chain
// starting from the "CurrentValue" until it meets "BaseValue". Only "simple"
// values are visited (currently it is GEP's and casts). Returns true if it
// successfully reached "BaseValue" and false otherwise.
// Fills "ChainToBase" array with all visited values. "BaseValue" is not
// recorded.
static bool findRematerializableChainToBasePointer(
SmallVectorImpl<Instruction*> &ChainToBase,
Value *CurrentValue, Value *BaseValue) {
// We have found a base value
if (CurrentValue == BaseValue) {
return true;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
ChainToBase.push_back(GEP);
return findRematerializableChainToBasePointer(ChainToBase,
GEP->getPointerOperand(),
BaseValue);
}
if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) {
if (!CI->isNoopCast(CI->getModule()->getDataLayout()))
return false;
ChainToBase.push_back(CI);
return findRematerializableChainToBasePointer(ChainToBase,
CI->getOperand(0), BaseValue);
}
// Not supported instruction in the chain
return false;
}
// Helper function for the "rematerializeLiveValues". Compute cost of the use
// chain we are going to rematerialize.
static unsigned
chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain,
TargetTransformInfo &TTI) {
unsigned Cost = 0;
for (Instruction *Instr : Chain) {
if (CastInst *CI = dyn_cast<CastInst>(Instr)) {
assert(CI->isNoopCast(CI->getModule()->getDataLayout()) &&
"non noop cast is found during rematerialization");
Type *SrcTy = CI->getOperand(0)->getType();
Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy);
} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) {
// Cost of the address calculation
Type *ValTy = GEP->getSourceElementType();
Cost += TTI.getAddressComputationCost(ValTy);
// And cost of the GEP itself
// TODO: Use TTI->getGEPCost here (it exists, but appears to be not
// allowed for the external usage)
if (!GEP->hasAllConstantIndices())
Cost += 2;
} else {
llvm_unreachable("unsupported instruciton type during rematerialization");
}
}
return Cost;
}
// From the statepoint live set pick values that are cheaper to recompute then
// to relocate. Remove this values from the live set, rematerialize them after
// statepoint and record them in "Info" structure. Note that similar to
// relocated values we don't do any user adjustments here.
static void rematerializeLiveValues(CallSite CS,
PartiallyConstructedSafepointRecord &Info,
TargetTransformInfo &TTI) {
const unsigned int ChainLengthThreshold = 10;
// Record values we are going to delete from this statepoint live set.
// We can not di this in following loop due to iterator invalidation.
SmallVector<Value *, 32> LiveValuesToBeDeleted;
for (Value *LiveValue: Info.LiveSet) {
// For each live pointer find it's defining chain
SmallVector<Instruction *, 3> ChainToBase;
assert(Info.PointerToBase.count(LiveValue));
bool FoundChain =
findRematerializableChainToBasePointer(ChainToBase,
LiveValue,
Info.PointerToBase[LiveValue]);
// Nothing to do, or chain is too long
if (!FoundChain ||
ChainToBase.size() == 0 ||
ChainToBase.size() > ChainLengthThreshold)
continue;
// Compute cost of this chain
unsigned Cost = chainToBasePointerCost(ChainToBase, TTI);
// TODO: We can also account for cases when we will be able to remove some
// of the rematerialized values by later optimization passes. I.e if
// we rematerialized several intersecting chains. Or if original values
// don't have any uses besides this statepoint.
// For invokes we need to rematerialize each chain twice - for normal and
// for unwind basic blocks. Model this by multiplying cost by two.
if (CS.isInvoke()) {
Cost *= 2;
}
// If it's too expensive - skip it
if (Cost >= RematerializationThreshold)
continue;
// Remove value from the live set
LiveValuesToBeDeleted.push_back(LiveValue);
// Clone instructions and record them inside "Info" structure
// Walk backwards to visit top-most instructions first
std::reverse(ChainToBase.begin(), ChainToBase.end());
// Utility function which clones all instructions from "ChainToBase"
// and inserts them before "InsertBefore". Returns rematerialized value
// which should be used after statepoint.
auto rematerializeChain = [&ChainToBase](Instruction *InsertBefore) {
Instruction *LastClonedValue = nullptr;
Instruction *LastValue = nullptr;
for (Instruction *Instr: ChainToBase) {
// Only GEP's and casts are suported as we need to be careful to not
// introduce any new uses of pointers not in the liveset.
// Note that it's fine to introduce new uses of pointers which were
// otherwise not used after this statepoint.
assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr));
Instruction *ClonedValue = Instr->clone();
ClonedValue->insertBefore(InsertBefore);
ClonedValue->setName(Instr->getName() + ".remat");
// If it is not first instruction in the chain then it uses previously
// cloned value. We should update it to use cloned value.
if (LastClonedValue) {
assert(LastValue);
ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue);
#ifndef NDEBUG
// Assert that cloned instruction does not use any instructions from
// this chain other than LastClonedValue
for (auto OpValue : ClonedValue->operand_values()) {
assert(std::find(ChainToBase.begin(), ChainToBase.end(), OpValue) ==
ChainToBase.end() &&
"incorrect use in rematerialization chain");
}
#endif
}
LastClonedValue = ClonedValue;
LastValue = Instr;
}
assert(LastClonedValue);
return LastClonedValue;
};
// Different cases for calls and invokes. For invokes we need to clone
// instructions both on normal and unwind path.
if (CS.isCall()) {
Instruction *InsertBefore = CS.getInstruction()->getNextNode();
assert(InsertBefore);
Instruction *RematerializedValue = rematerializeChain(InsertBefore);
Info.RematerializedValues[RematerializedValue] = LiveValue;
} else {
InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction());
Instruction *NormalInsertBefore =
&*Invoke->getNormalDest()->getFirstInsertionPt();
Instruction *UnwindInsertBefore =
&*Invoke->getUnwindDest()->getFirstInsertionPt();
Instruction *NormalRematerializedValue =
rematerializeChain(NormalInsertBefore);
Instruction *UnwindRematerializedValue =
rematerializeChain(UnwindInsertBefore);
Info.RematerializedValues[NormalRematerializedValue] = LiveValue;
Info.RematerializedValues[UnwindRematerializedValue] = LiveValue;
}
}
// Remove rematerializaed values from the live set
for (auto LiveValue: LiveValuesToBeDeleted) {
Info.LiveSet.erase(LiveValue);
}
}
static bool insertParsePoints(Function &F, DominatorTree &DT,
TargetTransformInfo &TTI,
SmallVectorImpl<CallSite> &ToUpdate) {
#ifndef NDEBUG
// sanity check the input
std::set<CallSite> Uniqued;
Uniqued.insert(ToUpdate.begin(), ToUpdate.end());
assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!");
for (CallSite CS : ToUpdate) {
assert(CS.getInstruction()->getParent()->getParent() == &F);
assert((UseDeoptBundles || isStatepoint(CS)) &&
"expected to already be a deopt statepoint");
}
#endif
// When inserting gc.relocates for invokes, we need to be able to insert at
// the top of the successor blocks. See the comment on
// normalForInvokeSafepoint on exactly what is needed. Note that this step
// may restructure the CFG.
for (CallSite CS : ToUpdate) {
if (!CS.isInvoke())
continue;
auto *II = cast<InvokeInst>(CS.getInstruction());
normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT);
normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT);
}
// A list of dummy calls added to the IR to keep various values obviously
// live in the IR. We'll remove all of these when done.
SmallVector<CallInst *, 64> Holders;
// Insert a dummy call with all of the arguments to the vm_state we'll need
// for the actual safepoint insertion. This ensures reference arguments in
// the deopt argument list are considered live through the safepoint (and
// thus makes sure they get relocated.)
for (CallSite CS : ToUpdate) {
SmallVector<Value *, 64> DeoptValues;
iterator_range<const Use *> DeoptStateRange =
UseDeoptBundles
? iterator_range<const Use *>(GetDeoptBundleOperands(CS))
: iterator_range<const Use *>(Statepoint(CS).vm_state_args());
for (Value *Arg : DeoptStateRange) {
assert(!isUnhandledGCPointerType(Arg->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(Arg->getType()))
DeoptValues.push_back(Arg);
}
insertUseHolderAfter(CS, DeoptValues, Holders);
}
SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size());
// A) Identify all gc pointers which are statically live at the given call
// site.
findLiveReferences(F, DT, ToUpdate, Records);
// B) Find the base pointers for each live pointer
/* scope for caching */ {
// Cache the 'defining value' relation used in the computation and
// insertion of base phis and selects. This ensures that we don't insert
// large numbers of duplicate base_phis.
DefiningValueMapTy DVCache;
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &info = Records[i];
findBasePointers(DT, DVCache, ToUpdate[i], info);
}
} // end of cache scope
// The base phi insertion logic (for any safepoint) may have inserted new
// instructions which are now live at some safepoint. The simplest such
// example is:
// loop:
// phi a <-- will be a new base_phi here
// safepoint 1 <-- that needs to be live here
// gep a + 1
// safepoint 2
// br loop
// We insert some dummy calls after each safepoint to definitely hold live
// the base pointers which were identified for that safepoint. We'll then
// ask liveness for _every_ base inserted to see what is now live. Then we
// remove the dummy calls.
Holders.reserve(Holders.size() + Records.size());
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &Info = Records[i];
SmallVector<Value *, 128> Bases;
for (auto Pair : Info.PointerToBase)
Bases.push_back(Pair.second);
insertUseHolderAfter(ToUpdate[i], Bases, Holders);
}
// By selecting base pointers, we've effectively inserted new uses. Thus, we
// need to rerun liveness. We may *also* have inserted new defs, but that's
// not the key issue.
recomputeLiveInValues(F, DT, ToUpdate, Records);
if (PrintBasePointers) {
for (auto &Info : Records) {
errs() << "Base Pairs: (w/Relocation)\n";
for (auto Pair : Info.PointerToBase) {
errs() << " derived ";
Pair.first->printAsOperand(errs(), false);
errs() << " base ";
Pair.second->printAsOperand(errs(), false);
errs() << "\n";
}
}
}
// It is possible that non-constant live variables have a constant base. For
// example, a GEP with a variable offset from a global. In this case we can
// remove it from the liveset. We already don't add constants to the liveset
// because we assume they won't move at runtime and the GC doesn't need to be
// informed about them. The same reasoning applies if the base is constant.
// Note that the relocation placement code relies on this filtering for
// correctness as it expects the base to be in the liveset, which isn't true
// if the base is constant.
for (auto &Info : Records)
for (auto &BasePair : Info.PointerToBase)
if (isa<Constant>(BasePair.second))
Info.LiveSet.erase(BasePair.first);
for (CallInst *CI : Holders)
CI->eraseFromParent();
Holders.clear();
// Do a limited scalarization of any live at safepoint vector values which
// contain pointers. This enables this pass to run after vectorization at
// the cost of some possible performance loss. Note: This is known to not
// handle updating of the side tables correctly which can lead to relocation
// bugs when the same vector is live at multiple statepoints. We're in the
// process of implementing the alternate lowering - relocating the
// vector-of-pointers as first class item and updating the backend to
// understand that - but that's not yet complete.
if (UseVectorSplit)
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &Info = Records[i];
Instruction *Statepoint = ToUpdate[i].getInstruction();
splitVectorValues(cast<Instruction>(Statepoint), Info.LiveSet,
Info.PointerToBase, DT);
}
// In order to reduce live set of statepoint we might choose to rematerialize
// some values instead of relocating them. This is purely an optimization and
// does not influence correctness.
for (size_t i = 0; i < Records.size(); i++)
rematerializeLiveValues(ToUpdate[i], Records[i], TTI);
// We need this to safely RAUW and delete call or invoke return values that
// may themselves be live over a statepoint. For details, please see usage in
// makeStatepointExplicitImpl.
std::vector<DeferredReplacement> Replacements;
// Now run through and replace the existing statepoints with new ones with
// the live variables listed. We do not yet update uses of the values being
// relocated. We have references to live variables that need to
// survive to the last iteration of this loop. (By construction, the
// previous statepoint can not be a live variable, thus we can and remove
// the old statepoint calls as we go.)
for (size_t i = 0; i < Records.size(); i++)
makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements);
ToUpdate.clear(); // prevent accident use of invalid CallSites
for (auto &PR : Replacements)
PR.doReplacement();
Replacements.clear();
for (auto &Info : Records) {
// These live sets may contain state Value pointers, since we replaced calls
// with operand bundles with calls wrapped in gc.statepoint, and some of
// those calls may have been def'ing live gc pointers. Clear these out to
// avoid accidentally using them.
//
// TODO: We should create a separate data structure that does not contain
// these live sets, and migrate to using that data structure from this point
// onward.
Info.LiveSet.clear();
Info.PointerToBase.clear();
}
// Do all the fixups of the original live variables to their relocated selves
SmallVector<Value *, 128> Live;
for (size_t i = 0; i < Records.size(); i++) {
PartiallyConstructedSafepointRecord &Info = Records[i];
// We can't simply save the live set from the original insertion. One of
// the live values might be the result of a call which needs a safepoint.
// That Value* no longer exists and we need to use the new gc_result.
// Thankfully, the live set is embedded in the statepoint (and updated), so
// we just grab that.
Statepoint Statepoint(Info.StatepointToken);
Live.insert(Live.end(), Statepoint.gc_args_begin(),
Statepoint.gc_args_end());
#ifndef NDEBUG
// Do some basic sanity checks on our liveness results before performing
// relocation. Relocation can and will turn mistakes in liveness results
// into non-sensical code which is must harder to debug.
// TODO: It would be nice to test consistency as well
assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) &&
"statepoint must be reachable or liveness is meaningless");
for (Value *V : Statepoint.gc_args()) {
if (!isa<Instruction>(V))
// Non-instruction values trivial dominate all possible uses
continue;
auto *LiveInst = cast<Instruction>(V);
assert(DT.isReachableFromEntry(LiveInst->getParent()) &&
"unreachable values should never be live");
assert(DT.dominates(LiveInst, Info.StatepointToken) &&
"basic SSA liveness expectation violated by liveness analysis");
}
#endif
}
unique_unsorted(Live);
#ifndef NDEBUG
// sanity check
for (auto *Ptr : Live)
assert(isHandledGCPointerType(Ptr->getType()) &&
"must be a gc pointer type");
#endif
relocationViaAlloca(F, DT, Live, Records);
return !Records.empty();
}
// Handles both return values and arguments for Functions and CallSites.
template <typename AttrHolder>
static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
unsigned Index) {
AttrBuilder R;
if (AH.getDereferenceableBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
AH.getDereferenceableBytes(Index)));
if (AH.getDereferenceableOrNullBytes(Index))
R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
AH.getDereferenceableOrNullBytes(Index)));
if (AH.doesNotAlias(Index))
R.addAttribute(Attribute::NoAlias);
if (!R.empty())
AH.setAttributes(AH.getAttributes().removeAttributes(
Ctx, Index, AttributeSet::get(Ctx, Index, R)));
}
void
RewriteStatepointsForGC::stripNonValidAttributesFromPrototype(Function &F) {
LLVMContext &Ctx = F.getContext();
for (Argument &A : F.args())
if (isa<PointerType>(A.getType()))
RemoveNonValidAttrAtIndex(Ctx, F, A.getArgNo() + 1);
if (isa<PointerType>(F.getReturnType()))
RemoveNonValidAttrAtIndex(Ctx, F, AttributeSet::ReturnIndex);
}
void RewriteStatepointsForGC::stripNonValidAttributesFromBody(Function &F) {
if (F.empty())
return;
LLVMContext &Ctx = F.getContext();
MDBuilder Builder(Ctx);
for (Instruction &I : instructions(F)) {
if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) {
assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!");
bool IsImmutableTBAA =
MD->getNumOperands() == 4 &&
mdconst::extract<ConstantInt>(MD->getOperand(3))->getValue() == 1;
if (!IsImmutableTBAA)
continue; // no work to do, MD_tbaa is already marked mutable
MDNode *Base = cast<MDNode>(MD->getOperand(0));
MDNode *Access = cast<MDNode>(MD->getOperand(1));
uint64_t Offset =
mdconst::extract<ConstantInt>(MD->getOperand(2))->getZExtValue();
MDNode *MutableTBAA =
Builder.createTBAAStructTagNode(Base, Access, Offset);
I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
}
if (CallSite CS = CallSite(&I)) {
for (int i = 0, e = CS.arg_size(); i != e; i++)
if (isa<PointerType>(CS.getArgument(i)->getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, i + 1);
if (isa<PointerType>(CS.getType()))
RemoveNonValidAttrAtIndex(Ctx, CS, AttributeSet::ReturnIndex);
}
}
}
/// Returns true if this function should be rewritten by this pass. The main
/// point of this function is as an extension point for custom logic.
static bool shouldRewriteStatepointsIn(Function &F) {
// TODO: This should check the GCStrategy
if (F.hasGC()) {
const auto &FunctionGCName = F.getGC();
const StringRef StatepointExampleName("statepoint-example");
const StringRef CoreCLRName("coreclr");
return (StatepointExampleName == FunctionGCName) ||
(CoreCLRName == FunctionGCName);
} else
return false;
}
void RewriteStatepointsForGC::stripNonValidAttributes(Module &M) {
#ifndef NDEBUG
assert(std::any_of(M.begin(), M.end(), shouldRewriteStatepointsIn) &&
"precondition!");
#endif
for (Function &F : M)
stripNonValidAttributesFromPrototype(F);
for (Function &F : M)
stripNonValidAttributesFromBody(F);
}
bool RewriteStatepointsForGC::runOnFunction(Function &F) {
// Nothing to do for declarations.
if (F.isDeclaration() || F.empty())
return false;
// Policy choice says not to rewrite - the most common reason is that we're
// compiling code without a GCStrategy.
if (!shouldRewriteStatepointsIn(F))
return false;
DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
auto NeedsRewrite = [](Instruction &I) {
if (UseDeoptBundles) {
if (ImmutableCallSite CS = ImmutableCallSite(&I))
return !callsGCLeafFunction(CS);
return false;
}
return isStatepoint(I);
};
// Gather all the statepoints which need rewritten. Be careful to only
// consider those in reachable code since we need to ask dominance queries
// when rewriting. We'll delete the unreachable ones in a moment.
SmallVector<CallSite, 64> ParsePointNeeded;
bool HasUnreachableStatepoint = false;
for (Instruction &I : instructions(F)) {
// TODO: only the ones with the flag set!
if (NeedsRewrite(I)) {
if (DT.isReachableFromEntry(I.getParent()))
ParsePointNeeded.push_back(CallSite(&I));
else
HasUnreachableStatepoint = true;
}
}
bool MadeChange = false;
// Delete any unreachable statepoints so that we don't have unrewritten
// statepoints surviving this pass. This makes testing easier and the
// resulting IR less confusing to human readers. Rather than be fancy, we
// just reuse a utility function which removes the unreachable blocks.
if (HasUnreachableStatepoint)
MadeChange |= removeUnreachableBlocks(F);
// Return early if no work to do.
if (ParsePointNeeded.empty())
return MadeChange;
// As a prepass, go ahead and aggressively destroy single entry phi nodes.
// These are created by LCSSA. They have the effect of increasing the size
// of liveness sets for no good reason. It may be harder to do this post
// insertion since relocations and base phis can confuse things.
for (BasicBlock &BB : F)
if (BB.getUniquePredecessor()) {
MadeChange = true;
FoldSingleEntryPHINodes(&BB);
}
// Before we start introducing relocations, we want to tweak the IR a bit to
// avoid unfortunate code generation effects. The main example is that we
// want to try to make sure the comparison feeding a branch is after any
// safepoints. Otherwise, we end up with a comparison of pre-relocation
// values feeding a branch after relocation. This is semantically correct,
// but results in extra register pressure since both the pre-relocation and
// post-relocation copies must be available in registers. For code without
// relocations this is handled elsewhere, but teaching the scheduler to
// reverse the transform we're about to do would be slightly complex.
// Note: This may extend the live range of the inputs to the icmp and thus
// increase the liveset of any statepoint we move over. This is profitable
// as long as all statepoints are in rare blocks. If we had in-register
// lowering for live values this would be a much safer transform.
auto getConditionInst = [](TerminatorInst *TI) -> Instruction* {
if (auto *BI = dyn_cast<BranchInst>(TI))
if (BI->isConditional())
return dyn_cast<Instruction>(BI->getCondition());
// TODO: Extend this to handle switches
return nullptr;
};
for (BasicBlock &BB : F) {
TerminatorInst *TI = BB.getTerminator();
if (auto *Cond = getConditionInst(TI))
// TODO: Handle more than just ICmps here. We should be able to move
// most instructions without side effects or memory access.
if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) {
MadeChange = true;
Cond->moveBefore(TI);
}
}
MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
return MadeChange;
}
// liveness computation via standard dataflow
// -------------------------------------------------------------------
// TODO: Consider using bitvectors for liveness, the set of potentially
// interesting values should be small and easy to pre-compute.
/// Compute the live-in set for the location rbegin starting from
/// the live-out set of the basic block
static void computeLiveInValues(BasicBlock::reverse_iterator rbegin,
BasicBlock::reverse_iterator rend,
DenseSet<Value *> &LiveTmp) {
for (BasicBlock::reverse_iterator ritr = rbegin; ritr != rend; ritr++) {
Instruction *I = &*ritr;
// KILL/Def - Remove this definition from LiveIn
LiveTmp.erase(I);
// Don't consider *uses* in PHI nodes, we handle their contribution to
// predecessor blocks when we seed the LiveOut sets
if (isa<PHINode>(I))
continue;
// USE - Add to the LiveIn set for this instruction
for (Value *V : I->operands()) {
assert(!isUnhandledGCPointerType(V->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
// The choice to exclude all things constant here is slightly subtle.
// There are two independent reasons:
// - We assume that things which are constant (from LLVM's definition)
// do not move at runtime. For example, the address of a global
// variable is fixed, even though it's contents may not be.
// - Second, we can't disallow arbitrary inttoptr constants even
// if the language frontend does. Optimization passes are free to
// locally exploit facts without respect to global reachability. This
// can create sections of code which are dynamically unreachable and
// contain just about anything. (see constants.ll in tests)
LiveTmp.insert(V);
}
}
}
}
static void computeLiveOutSeed(BasicBlock *BB, DenseSet<Value *> &LiveTmp) {
for (BasicBlock *Succ : successors(BB)) {
const BasicBlock::iterator E(Succ->getFirstNonPHI());
for (BasicBlock::iterator I = Succ->begin(); I != E; I++) {
PHINode *Phi = cast<PHINode>(&*I);
Value *V = Phi->getIncomingValueForBlock(BB);
assert(!isUnhandledGCPointerType(V->getType()) &&
"support for FCA unimplemented");
if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
LiveTmp.insert(V);
}
}
}
}
static DenseSet<Value *> computeKillSet(BasicBlock *BB) {
DenseSet<Value *> KillSet;
for (Instruction &I : *BB)
if (isHandledGCPointerType(I.getType()))
KillSet.insert(&I);
return KillSet;
}
#ifndef NDEBUG
/// Check that the items in 'Live' dominate 'TI'. This is used as a basic
/// sanity check for the liveness computation.
static void checkBasicSSA(DominatorTree &DT, DenseSet<Value *> &Live,
TerminatorInst *TI, bool TermOkay = false) {
for (Value *V : Live) {
if (auto *I = dyn_cast<Instruction>(V)) {
// The terminator can be a member of the LiveOut set. LLVM's definition
// of instruction dominance states that V does not dominate itself. As
// such, we need to special case this to allow it.
if (TermOkay && TI == I)
continue;
assert(DT.dominates(I, TI) &&
"basic SSA liveness expectation violated by liveness analysis");
}
}
}
/// Check that all the liveness sets used during the computation of liveness
/// obey basic SSA properties. This is useful for finding cases where we miss
/// a def.
static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data,
BasicBlock &BB) {
checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator());
checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true);
checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator());
}
#endif
static void computeLiveInValues(DominatorTree &DT, Function &F,
GCPtrLivenessData &Data) {
SmallSetVector<BasicBlock *, 200> Worklist;
auto AddPredsToWorklist = [&](BasicBlock *BB) {
// We use a SetVector so that we don't have duplicates in the worklist.
Worklist.insert(pred_begin(BB), pred_end(BB));
};
auto NextItem = [&]() {
BasicBlock *BB = Worklist.back();
Worklist.pop_back();
return BB;
};
// Seed the liveness for each individual block
for (BasicBlock &BB : F) {
Data.KillSet[&BB] = computeKillSet(&BB);
Data.LiveSet[&BB].clear();
computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]);
#ifndef NDEBUG
for (Value *Kill : Data.KillSet[&BB])
assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
#endif
Data.LiveOut[&BB] = DenseSet<Value *>();
computeLiveOutSeed(&BB, Data.LiveOut[&BB]);
Data.LiveIn[&BB] = Data.LiveSet[&BB];
set_union(Data.LiveIn[&BB], Data.LiveOut[&BB]);
set_subtract(Data.LiveIn[&BB], Data.KillSet[&BB]);
if (!Data.LiveIn[&BB].empty())
AddPredsToWorklist(&BB);
}
// Propagate that liveness until stable
while (!Worklist.empty()) {
BasicBlock *BB = NextItem();
// Compute our new liveout set, then exit early if it hasn't changed
// despite the contribution of our successor.
DenseSet<Value *> LiveOut = Data.LiveOut[BB];
const auto OldLiveOutSize = LiveOut.size();
for (BasicBlock *Succ : successors(BB)) {
assert(Data.LiveIn.count(Succ));
set_union(LiveOut, Data.LiveIn[Succ]);
}
// assert OutLiveOut is a subset of LiveOut
if (OldLiveOutSize == LiveOut.size()) {
// If the sets are the same size, then we didn't actually add anything
// when unioning our successors LiveIn Thus, the LiveIn of this block
// hasn't changed.
continue;
}
Data.LiveOut[BB] = LiveOut;
// Apply the effects of this basic block
DenseSet<Value *> LiveTmp = LiveOut;
set_union(LiveTmp, Data.LiveSet[BB]);
set_subtract(LiveTmp, Data.KillSet[BB]);
assert(Data.LiveIn.count(BB));
const DenseSet<Value *> &OldLiveIn = Data.LiveIn[BB];
// assert: OldLiveIn is a subset of LiveTmp
if (OldLiveIn.size() != LiveTmp.size()) {
Data.LiveIn[BB] = LiveTmp;
AddPredsToWorklist(BB);
}
} // while( !worklist.empty() )
#ifndef NDEBUG
// Sanity check our output against SSA properties. This helps catch any
// missing kills during the above iteration.
for (BasicBlock &BB : F) {
checkBasicSSA(DT, Data, BB);
}
#endif
}
static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data,
StatepointLiveSetTy &Out) {
BasicBlock *BB = Inst->getParent();
// Note: The copy is intentional and required
assert(Data.LiveOut.count(BB));
DenseSet<Value *> LiveOut = Data.LiveOut[BB];
// We want to handle the statepoint itself oddly. It's
// call result is not live (normal), nor are it's arguments
// (unless they're used again later). This adjustment is
// specifically what we need to relocate
BasicBlock::reverse_iterator rend(Inst->getIterator());
computeLiveInValues(BB->rbegin(), rend, LiveOut);
LiveOut.erase(Inst);
Out.insert(LiveOut.begin(), LiveOut.end());
}
static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
const CallSite &CS,
PartiallyConstructedSafepointRecord &Info) {
Instruction *Inst = CS.getInstruction();
StatepointLiveSetTy Updated;
findLiveSetAtInst(Inst, RevisedLivenessData, Updated);
#ifndef NDEBUG
DenseSet<Value *> Bases;
for (auto KVPair : Info.PointerToBase) {
Bases.insert(KVPair.second);
}
#endif
// We may have base pointers which are now live that weren't before. We need
// to update the PointerToBase structure to reflect this.
for (auto V : Updated)
if (!Info.PointerToBase.count(V)) {
assert(Bases.count(V) && "can't find base for unexpected live value");
Info.PointerToBase[V] = V;
continue;
}
#ifndef NDEBUG
for (auto V : Updated) {
assert(Info.PointerToBase.count(V) &&
"must be able to find base for live value");
}
#endif
// Remove any stale base mappings - this can happen since our liveness is
// more precise then the one inherent in the base pointer analysis
DenseSet<Value *> ToErase;
for (auto KVPair : Info.PointerToBase)
if (!Updated.count(KVPair.first))
ToErase.insert(KVPair.first);
for (auto V : ToErase)
Info.PointerToBase.erase(V);
#ifndef NDEBUG
for (auto KVPair : Info.PointerToBase)
assert(Updated.count(KVPair.first) && "record for non-live value");
#endif
Info.LiveSet = Updated;
}
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