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llvm/lib/CodeGen/IfConversion.cpp
Evan Cheng 309db7c947 If converter was being too cute. It look for root BBs (which don't have 
successors) and use inverse depth first search to traverse the BBs. However
that doesn't work when the CFG has infinite loops. Simply do a linear
traversal of all BBs work just fine.

rdar://9344645


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130324 91177308-0d34-0410-b5e6-96231b3b80d8
2011-04-27 19:32:43 +00:00

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//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level if-conversion pass.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ifcvt"
#include "BranchFolding.h"
#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetInstrItineraries.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
// Hidden options for help debugging.
static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
static cl::opt<bool> DisableSimple("disable-ifcvt-simple",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev",
cl::init(false), cl::Hidden);
static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond",
cl::init(false), cl::Hidden);
static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold",
cl::init(true), cl::Hidden);
STATISTIC(NumSimple, "Number of simple if-conversions performed");
STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed");
STATISTIC(NumTriangle, "Number of triangle if-conversions performed");
STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed");
STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
STATISTIC(NumDiamonds, "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs, "Number of if-converted blocks");
STATISTIC(NumDupBBs, "Number of duplicated blocks");
namespace {
class IfConverter : public MachineFunctionPass {
enum IfcvtKind {
ICNotClassfied, // BB data valid, but not classified.
ICSimpleFalse, // Same as ICSimple, but on the false path.
ICSimple, // BB is entry of an one split, no rejoin sub-CFG.
ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition.
ICTriangleRev, // Same as ICTriangle, but true path rev condition.
ICTriangleFalse, // Same as ICTriangle, but on the false path.
ICTriangle, // BB is entry of a triangle sub-CFG.
ICDiamond // BB is entry of a diamond sub-CFG.
};
/// BBInfo - One per MachineBasicBlock, this is used to cache the result
/// if-conversion feasibility analysis. This includes results from
/// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
/// classification, and common tail block of its successors (if it's a
/// diamond shape), its size, whether it's predicable, and whether any
/// instruction can clobber the 'would-be' predicate.
///
/// IsDone - True if BB is not to be considered for ifcvt.
/// IsBeingAnalyzed - True if BB is currently being analyzed.
/// IsAnalyzed - True if BB has been analyzed (info is still valid).
/// IsEnqueued - True if BB has been enqueued to be ifcvt'ed.
/// IsBrAnalyzable - True if AnalyzeBranch() returns false.
/// HasFallThrough - True if BB may fallthrough to the following BB.
/// IsUnpredicable - True if BB is known to be unpredicable.
/// ClobbersPred - True if BB could modify predicates (e.g. has
/// cmp, call, etc.)
/// NonPredSize - Number of non-predicated instructions.
/// ExtraCost - Extra cost for multi-cycle instructions.
/// ExtraCost2 - Some instructions are slower when predicated
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
/// Predicate - Predicate used in the BB.
struct BBInfo {
bool IsDone : 1;
bool IsBeingAnalyzed : 1;
bool IsAnalyzed : 1;
bool IsEnqueued : 1;
bool IsBrAnalyzable : 1;
bool HasFallThrough : 1;
bool IsUnpredicable : 1;
bool CannotBeCopied : 1;
bool ClobbersPred : 1;
unsigned NonPredSize;
unsigned ExtraCost;
unsigned ExtraCost2;
MachineBasicBlock *BB;
MachineBasicBlock *TrueBB;
MachineBasicBlock *FalseBB;
SmallVector<MachineOperand, 4> BrCond;
SmallVector<MachineOperand, 4> Predicate;
BBInfo() : IsDone(false), IsBeingAnalyzed(false),
IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false),
HasFallThrough(false), IsUnpredicable(false),
CannotBeCopied(false), ClobbersPred(false), NonPredSize(0),
ExtraCost(0), ExtraCost2(0), BB(0), TrueBB(0), FalseBB(0) {}
};
/// IfcvtToken - Record information about pending if-conversions to attempt:
/// BBI - Corresponding BBInfo.
/// Kind - Type of block. See IfcvtKind.
/// NeedSubsumption - True if the to-be-predicated BB has already been
/// predicated.
/// NumDups - Number of instructions that would be duplicated due
/// to this if-conversion. (For diamonds, the number of
/// identical instructions at the beginnings of both
/// paths).
/// NumDups2 - For diamonds, the number of identical instructions
/// at the ends of both paths.
struct IfcvtToken {
BBInfo &BBI;
IfcvtKind Kind;
bool NeedSubsumption;
unsigned NumDups;
unsigned NumDups2;
IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0)
: BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {}
};
/// BBAnalysis - Results of if-conversion feasibility analysis indexed by
/// basic block number.
std::vector<BBInfo> BBAnalysis;
const TargetLowering *TLI;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
const InstrItineraryData *InstrItins;
const MachineLoopInfo *MLI;
bool MadeChange;
int FnNum;
public:
static char ID;
IfConverter() : MachineFunctionPass(ID), FnNum(-1) {
initializeIfConverterPass(*PassRegistry::getPassRegistry());
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<MachineLoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "If Converter"; }
private:
bool ReverseBranchCondition(BBInfo &BBI);
bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
float Prediction, float Confidence) const;
bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch, unsigned &Dups,
float Prediction, float Confidence) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
unsigned &Dups1, unsigned &Dups2) const;
void ScanInstructions(BBInfo &BBI);
BBInfo &AnalyzeBlock(MachineBasicBlock *BB,
std::vector<IfcvtToken*> &Tokens);
bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Cond,
bool isTriangle = false, bool RevBranch = false);
void AnalyzeBlocks(MachineFunction &MF, std::vector<IfcvtToken*> &Tokens);
void InvalidatePreds(MachineBasicBlock *BB);
void RemoveExtraEdges(BBInfo &BBI);
bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind);
bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
unsigned NumDups1, unsigned NumDups2);
void PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs);
void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
bool IgnoreBr = false);
void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
bool MeetIfcvtSizeLimit(MachineBasicBlock &BB,
unsigned Cycle, unsigned Extra,
float Prediction, float Confidence) const {
return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra,
Prediction, Confidence);
}
bool MeetIfcvtSizeLimit(MachineBasicBlock &TBB,
unsigned TCycle, unsigned TExtra,
MachineBasicBlock &FBB,
unsigned FCycle, unsigned FExtra,
float Prediction, float Confidence) const {
return TCycle > 0 && FCycle > 0 &&
TII->isProfitableToIfCvt(TBB, TCycle, TExtra, FBB, FCycle, FExtra,
Prediction, Confidence);
}
// blockAlwaysFallThrough - Block ends without a terminator.
bool blockAlwaysFallThrough(BBInfo &BBI) const {
return BBI.IsBrAnalyzable && BBI.TrueBB == NULL;
}
// IfcvtTokenCmp - Used to sort if-conversion candidates.
static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) {
int Incr1 = (C1->Kind == ICDiamond)
? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups;
int Incr2 = (C2->Kind == ICDiamond)
? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups;
if (Incr1 > Incr2)
return true;
else if (Incr1 == Incr2) {
// Favors subsumption.
if (C1->NeedSubsumption == false && C2->NeedSubsumption == true)
return true;
else if (C1->NeedSubsumption == C2->NeedSubsumption) {
// Favors diamond over triangle, etc.
if ((unsigned)C1->Kind < (unsigned)C2->Kind)
return true;
else if (C1->Kind == C2->Kind)
return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber();
}
}
return false;
}
};
char IfConverter::ID = 0;
}
INITIALIZE_PASS_BEGIN(IfConverter, "if-converter", "If Converter", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(IfConverter, "if-converter", "If Converter", false, false)
FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); }
bool IfConverter::runOnMachineFunction(MachineFunction &MF) {
TLI = MF.getTarget().getTargetLowering();
TII = MF.getTarget().getInstrInfo();
TRI = MF.getTarget().getRegisterInfo();
MLI = &getAnalysis<MachineLoopInfo>();
InstrItins = MF.getTarget().getInstrItineraryData();
if (!TII) return false;
// Tail merge tend to expose more if-conversion opportunities.
BranchFolder BF(true);
bool BFChange = BF.OptimizeFunction(MF, TII,
MF.getTarget().getRegisterInfo(),
getAnalysisIfAvailable<MachineModuleInfo>());
DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'"
<< MF.getFunction()->getName() << "\'");
if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) {
DEBUG(dbgs() << " skipped\n");
return false;
}
DEBUG(dbgs() << "\n");
MF.RenumberBlocks();
BBAnalysis.resize(MF.getNumBlockIDs());
std::vector<IfcvtToken*> Tokens;
MadeChange = false;
unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle +
NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds;
while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) {
// Do an initial analysis for each basic block and find all the potential
// candidates to perform if-conversion.
bool Change = false;
AnalyzeBlocks(MF, Tokens);
while (!Tokens.empty()) {
IfcvtToken *Token = Tokens.back();
Tokens.pop_back();
BBInfo &BBI = Token->BBI;
IfcvtKind Kind = Token->Kind;
unsigned NumDups = Token->NumDups;
unsigned NumDups2 = Token->NumDups2;
delete Token;
// If the block has been evicted out of the queue or it has already been
// marked dead (due to it being predicated), then skip it.
if (BBI.IsDone)
BBI.IsEnqueued = false;
if (!BBI.IsEnqueued)
continue;
BBI.IsEnqueued = false;
bool RetVal = false;
switch (Kind) {
default: assert(false && "Unexpected!");
break;
case ICSimple:
case ICSimpleFalse: {
bool isFalse = Kind == ICSimpleFalse;
if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break;
DEBUG(dbgs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ?
" false" : "")
<< "): BB#" << BBI.BB->getNumber() << " ("
<< ((Kind == ICSimpleFalse)
? BBI.FalseBB->getNumber()
: BBI.TrueBB->getNumber()) << ") ");
RetVal = IfConvertSimple(BBI, Kind);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) {
if (isFalse) ++NumSimpleFalse;
else ++NumSimple;
}
break;
}
case ICTriangle:
case ICTriangleRev:
case ICTriangleFalse:
case ICTriangleFRev: {
bool isFalse = Kind == ICTriangleFalse;
bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev);
if (DisableTriangle && !isFalse && !isRev) break;
if (DisableTriangleR && !isFalse && isRev) break;
if (DisableTriangleF && isFalse && !isRev) break;
if (DisableTriangleFR && isFalse && isRev) break;
DEBUG(dbgs() << "Ifcvt (Triangle");
if (isFalse)
DEBUG(dbgs() << " false");
if (isRev)
DEBUG(dbgs() << " rev");
DEBUG(dbgs() << "): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:"
<< BBI.FalseBB->getNumber() << ") ");
RetVal = IfConvertTriangle(BBI, Kind);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) {
if (isFalse) {
if (isRev) ++NumTriangleFRev;
else ++NumTriangleFalse;
} else {
if (isRev) ++NumTriangleRev;
else ++NumTriangle;
}
}
break;
}
case ICDiamond: {
if (DisableDiamond) break;
DEBUG(dbgs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
<< BBI.TrueBB->getNumber() << ",F:"
<< BBI.FalseBB->getNumber() << ") ");
RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2);
DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n");
if (RetVal) ++NumDiamonds;
break;
}
}
Change |= RetVal;
NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev +
NumTriangleFalse + NumTriangleFRev + NumDiamonds;
if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit)
break;
}
if (!Change)
break;
MadeChange |= Change;
}
// Delete tokens in case of early exit.
while (!Tokens.empty()) {
IfcvtToken *Token = Tokens.back();
Tokens.pop_back();
delete Token;
}
Tokens.clear();
BBAnalysis.clear();
if (MadeChange && IfCvtBranchFold) {
BranchFolder BF(false);
BF.OptimizeFunction(MF, TII,
MF.getTarget().getRegisterInfo(),
getAnalysisIfAvailable<MachineModuleInfo>());
}
MadeChange |= BFChange;
return MadeChange;
}
/// findFalseBlock - BB has a fallthrough. Find its 'false' successor given
/// its 'true' successor.
static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB,
MachineBasicBlock *TrueBB) {
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
E = BB->succ_end(); SI != E; ++SI) {
MachineBasicBlock *SuccBB = *SI;
if (SuccBB != TrueBB)
return SuccBB;
}
return NULL;
}
/// ReverseBranchCondition - Reverse the condition of the end of the block
/// branch. Swap block's 'true' and 'false' successors.
bool IfConverter::ReverseBranchCondition(BBInfo &BBI) {
DebugLoc dl; // FIXME: this is nowhere
if (!TII->ReverseBranchCondition(BBI.BrCond)) {
TII->RemoveBranch(*BBI.BB);
TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl);
std::swap(BBI.TrueBB, BBI.FalseBB);
return true;
}
return false;
}
/// getNextBlock - Returns the next block in the function blocks ordering. If
/// it is the end, returns NULL.
static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) {
MachineFunction::iterator I = BB;
MachineFunction::iterator E = BB->getParent()->end();
if (++I == E)
return NULL;
return I;
}
/// ValidSimple - Returns true if the 'true' block (along with its
/// predecessor) forms a valid simple shape for ifcvt. It also returns the
/// number of instructions that the ifcvt would need to duplicate if performed
/// in Dups.
bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups,
float Prediction, float Confidence) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
if (TrueBBI.IsBrAnalyzable)
return false;
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied ||
!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize,
Prediction, Confidence))
return false;
Dups = TrueBBI.NonPredSize;
}
return true;
}
/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
/// If 'FalseBranch' is true, it checks if 'true' block's false branch
/// branches to the 'false' block rather than the other way around. It also
/// returns the number of instructions that the ifcvt would need to duplicate
/// if performed in 'Dups'.
bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
bool FalseBranch, unsigned &Dups,
float Prediction, float Confidence) const {
Dups = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone)
return false;
if (TrueBBI.BB->pred_size() > 1) {
if (TrueBBI.CannotBeCopied)
return false;
unsigned Size = TrueBBI.NonPredSize;
if (TrueBBI.IsBrAnalyzable) {
if (TrueBBI.TrueBB && TrueBBI.BrCond.empty())
// Ends with an unconditional branch. It will be removed.
--Size;
else {
MachineBasicBlock *FExit = FalseBranch
? TrueBBI.TrueBB : TrueBBI.FalseBB;
if (FExit)
// Require a conditional branch
++Size;
}
}
if (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size,
Prediction, Confidence))
return false;
Dups = Size;
}
MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
MachineFunction::iterator I = TrueBBI.BB;
if (++I == TrueBBI.BB->getParent()->end())
return false;
TExit = I;
}
return TExit && TExit == FalseBBI.BB;
}
/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI,
unsigned &Dups1, unsigned &Dups2) const {
Dups1 = Dups2 = 0;
if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone ||
FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone)
return false;
MachineBasicBlock *TT = TrueBBI.TrueBB;
MachineBasicBlock *FT = FalseBBI.TrueBB;
if (!TT && blockAlwaysFallThrough(TrueBBI))
TT = getNextBlock(TrueBBI.BB);
if (!FT && blockAlwaysFallThrough(FalseBBI))
FT = getNextBlock(FalseBBI.BB);
if (TT != FT)
return false;
if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable))
return false;
if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1)
return false;
// FIXME: Allow true block to have an early exit?
if (TrueBBI.FalseBB || FalseBBI.FalseBB ||
(TrueBBI.ClobbersPred && FalseBBI.ClobbersPred))
return false;
// Count duplicate instructions at the beginning of the true and false blocks.
MachineBasicBlock::iterator TIB = TrueBBI.BB->begin();
MachineBasicBlock::iterator FIB = FalseBBI.BB->begin();
MachineBasicBlock::iterator TIE = TrueBBI.BB->end();
MachineBasicBlock::iterator FIE = FalseBBI.BB->end();
while (TIB != TIE && FIB != FIE) {
// Skip dbg_value instructions. These do not count.
if (TIB->isDebugValue()) {
while (TIB != TIE && TIB->isDebugValue())
++TIB;
if (TIB == TIE)
break;
}
if (FIB->isDebugValue()) {
while (FIB != FIE && FIB->isDebugValue())
++FIB;
if (FIB == FIE)
break;
}
if (!TIB->isIdenticalTo(FIB))
break;
++Dups1;
++TIB;
++FIB;
}
// Now, in preparation for counting duplicate instructions at the ends of the
// blocks, move the end iterators up past any branch instructions.
while (TIE != TIB) {
--TIE;
if (!TIE->getDesc().isBranch())
break;
}
while (FIE != FIB) {
--FIE;
if (!FIE->getDesc().isBranch())
break;
}
// If Dups1 includes all of a block, then don't count duplicate
// instructions at the end of the blocks.
if (TIB == TIE || FIB == FIE)
return true;
// Count duplicate instructions at the ends of the blocks.
while (TIE != TIB && FIE != FIB) {
// Skip dbg_value instructions. These do not count.
if (TIE->isDebugValue()) {
while (TIE != TIB && TIE->isDebugValue())
--TIE;
if (TIE == TIB)
break;
}
if (FIE->isDebugValue()) {
while (FIE != FIB && FIE->isDebugValue())
--FIE;
if (FIE == FIB)
break;
}
if (!TIE->isIdenticalTo(FIE))
break;
++Dups2;
--TIE;
--FIE;
}
return true;
}
/// ScanInstructions - Scan all the instructions in the block to determine if
/// the block is predicable. In most cases, that means all the instructions
/// in the block are isPredicable(). Also checks if the block contains any
/// instruction which can clobber a predicate (e.g. condition code register).
/// If so, the block is not predicable unless it's the last instruction.
void IfConverter::ScanInstructions(BBInfo &BBI) {
if (BBI.IsDone)
return;
bool AlreadyPredicated = BBI.Predicate.size() > 0;
// First analyze the end of BB branches.
BBI.TrueBB = BBI.FalseBB = NULL;
BBI.BrCond.clear();
BBI.IsBrAnalyzable =
!TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL;
if (BBI.BrCond.size()) {
// No false branch. This BB must end with a conditional branch and a
// fallthrough.
if (!BBI.FalseBB)
BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB);
if (!BBI.FalseBB) {
// Malformed bcc? True and false blocks are the same?
BBI.IsUnpredicable = true;
return;
}
}
// Then scan all the instructions.
BBI.NonPredSize = 0;
BBI.ExtraCost = 0;
BBI.ExtraCost2 = 0;
BBI.ClobbersPred = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
if (I->isDebugValue())
continue;
const TargetInstrDesc &TID = I->getDesc();
if (TID.isNotDuplicable())
BBI.CannotBeCopied = true;
bool isPredicated = TII->isPredicated(I);
bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch();
if (!isCondBr) {
if (!isPredicated) {
BBI.NonPredSize++;
unsigned ExtraPredCost = 0;
unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I,
&ExtraPredCost);
if (NumCycles > 1)
BBI.ExtraCost += NumCycles-1;
BBI.ExtraCost2 += ExtraPredCost;
} else if (!AlreadyPredicated) {
// FIXME: This instruction is already predicated before the
// if-conversion pass. It's probably something like a conditional move.
// Mark this block unpredicable for now.
BBI.IsUnpredicable = true;
return;
}
}
if (BBI.ClobbersPred && !isPredicated) {
// Predicate modification instruction should end the block (except for
// already predicated instructions and end of block branches).
if (isCondBr) {
// A conditional branch is not predicable, but it may be eliminated.
continue;
}
// Predicate may have been modified, the subsequent (currently)
// unpredicated instructions cannot be correctly predicated.
BBI.IsUnpredicable = true;
return;
}
// FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are
// still potentially predicable.
std::vector<MachineOperand> PredDefs;
if (TII->DefinesPredicate(I, PredDefs))
BBI.ClobbersPred = true;
if (!TII->isPredicable(I)) {
BBI.IsUnpredicable = true;
return;
}
}
}
/// FeasibilityAnalysis - Determine if the block is a suitable candidate to be
/// predicated by the specified predicate.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
SmallVectorImpl<MachineOperand> &Pred,
bool isTriangle, bool RevBranch) {
// If the block is dead or unpredicable, then it cannot be predicated.
if (BBI.IsDone || BBI.IsUnpredicable)
return false;
// If it is already predicated, check if its predicate subsumes the new
// predicate.
if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
return false;
if (BBI.BrCond.size()) {
if (!isTriangle)
return false;
// Test predicate subsumption.
SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end());
SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
if (RevBranch) {
if (TII->ReverseBranchCondition(Cond))
return false;
}
if (TII->ReverseBranchCondition(RevPred) ||
!TII->SubsumesPredicate(Cond, RevPred))
return false;
}
return true;
}
/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB,
std::vector<IfcvtToken*> &Tokens) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed)
return BBI;
BBI.BB = BB;
BBI.IsBeingAnalyzed = true;
ScanInstructions(BBI);
// Unanalyzable or ends with fallthrough or unconditional branch.
if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Do not ifcvt if either path is a back edge to the entry block.
if (BBI.TrueBB == BB || BBI.FalseBB == BB) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
// Do not ifcvt if true and false fallthrough blocks are the same.
if (!BBI.FalseBB) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens);
BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens);
if (TrueBBI.IsDone && FalseBBI.IsDone) {
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
unsigned Dups = 0;
unsigned Dups2 = 0;
bool TNeedSub = TrueBBI.Predicate.size() > 0;
bool FNeedSub = FalseBBI.Predicate.size() > 0;
bool Enqueued = false;
// Try to predict the branch, using loop info to guide us.
// General heuristics are:
// - backedge -> 90% taken
// - early exit -> 20% taken
// - branch predictor confidence -> 90%
float Prediction = 0.5f;
float Confidence = 0.9f;
MachineLoop *Loop = MLI->getLoopFor(BB);
if (Loop) {
if (TrueBBI.BB == Loop->getHeader())
Prediction = 0.9f;
else if (FalseBBI.BB == Loop->getHeader())
Prediction = 0.1f;
MachineLoop *TrueLoop = MLI->getLoopFor(TrueBBI.BB);
MachineLoop *FalseLoop = MLI->getLoopFor(FalseBBI.BB);
if (!TrueLoop || TrueLoop->getParentLoop() == Loop)
Prediction = 0.2f;
else if (!FalseLoop || FalseLoop->getParentLoop() == Loop)
Prediction = 0.8f;
}
if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, (TrueBBI.NonPredSize - (Dups + Dups2) +
TrueBBI.ExtraCost), TrueBBI.ExtraCost2,
*FalseBBI.BB, (FalseBBI.NonPredSize - (Dups + Dups2) +
FalseBBI.ExtraCost),FalseBBI.ExtraCost2,
Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
// | |
// TBB FBB
// \ /
// TailBB
// Note TailBB can be empty.
Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups,
Dups2));
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
// Triangle:
// EBB
// | \_
// | |
// | TBB
// | /
// FBB
Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups));
Enqueued = true;
}
if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(TrueBBI, Dups, Prediction, Confidence) &&
MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost,
TrueBBI.ExtraCost2, Prediction, Confidence) &&
FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
// Simple (split, no rejoin):
// EBB
// | \_
// | |
// | TBB---> exit
// |
// FBB
Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups));
Enqueued = true;
}
if (CanRevCond) {
// Try the other path...
if (ValidTriangle(FalseBBI, TrueBBI, false, Dups,
1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups));
Enqueued = true;
}
if (ValidTriangle(FalseBBI, TrueBBI, true, Dups,
1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups));
Enqueued = true;
}
if (ValidSimple(FalseBBI, Dups, 1.0-Prediction, Confidence) &&
MeetIfcvtSizeLimit(*FalseBBI.BB,
FalseBBI.NonPredSize + FalseBBI.ExtraCost,
FalseBBI.ExtraCost2, 1.0-Prediction, Confidence) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups));
Enqueued = true;
}
}
BBI.IsEnqueued = Enqueued;
BBI.IsBeingAnalyzed = false;
BBI.IsAnalyzed = true;
return BBI;
}
/// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion
/// candidates.
void IfConverter::AnalyzeBlocks(MachineFunction &MF,
std::vector<IfcvtToken*> &Tokens) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *BB = I;
AnalyzeBlock(BB, Tokens);
}
// Sort to favor more complex ifcvt scheme.
std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp);
}
/// canFallThroughTo - Returns true either if ToBB is the next block after BB or
/// that all the intervening blocks are empty (given BB can fall through to its
/// next block).
static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) {
MachineFunction::iterator PI = BB;
MachineFunction::iterator I = llvm::next(PI);
MachineFunction::iterator TI = ToBB;
MachineFunction::iterator E = BB->getParent()->end();
while (I != TI) {
// Check isSuccessor to avoid case where the next block is empty, but
// it's not a successor.
if (I == E || !I->empty() || !PI->isSuccessor(I))
return false;
PI = I++;
}
return true;
}
/// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed
/// to determine if it can be if-converted. If predecessor is already enqueued,
/// dequeue it!
void IfConverter::InvalidatePreds(MachineBasicBlock *BB) {
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()];
if (PBBI.IsDone || PBBI.BB == BB)
continue;
PBBI.IsAnalyzed = false;
PBBI.IsEnqueued = false;
}
}
/// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB.
///
static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB,
const TargetInstrInfo *TII) {
DebugLoc dl; // FIXME: this is nowhere
SmallVector<MachineOperand, 0> NoCond;
TII->InsertBranch(*BB, ToBB, NULL, NoCond, dl);
}
/// RemoveExtraEdges - Remove true / false edges if either / both are no longer
/// successors.
void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
MachineBasicBlock *TBB = NULL, *FBB = NULL;
SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond))
BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
}
/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
/// modeled as read + write (sort like two-address instructions). These
/// routines track register liveness and add implicit uses to if-converted
/// instructions to conform to the model.
static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
const TargetRegisterInfo *TRI) {
for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
E = BB->livein_end(); I != E; ++I) {
unsigned Reg = *I;
Redefs.insert(Reg);
for (const unsigned *Subreg = TRI->getSubRegisters(Reg);
*Subreg; ++Subreg)
Redefs.insert(*Subreg);
}
}
static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
const TargetRegisterInfo *TRI,
bool AddImpUse = false) {
SmallVector<unsigned, 4> Defs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (MO.isDef())
Defs.push_back(Reg);
else if (MO.isKill()) {
Redefs.erase(Reg);
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
Redefs.erase(*SR);
}
}
for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
unsigned Reg = Defs[i];
if (Redefs.count(Reg)) {
if (AddImpUse)
// Treat predicated update as read + write.
MI->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
true/*IsImp*/,false/*IsKill*/));
} else {
Redefs.insert(Reg);
for (const unsigned *SR = TRI->getSubRegisters(Reg); *SR; ++SR)
Redefs.insert(*SR);
}
}
}
static void UpdatePredRedefs(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator E,
SmallSet<unsigned,4> &Redefs,
const TargetRegisterInfo *TRI) {
while (I != E) {
UpdatePredRedefs(I, Redefs, TRI);
++I;
}
}
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
if (Kind == ICSimpleFalse)
std::swap(CvtBBI, NextBBI);
if (CvtBBI->IsDone ||
(CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
// Something has changed. It's no longer safe to predicate this block.
BBI.IsAnalyzed = false;
CvtBBI->IsAnalyzed = false;
return false;
}
if (Kind == ICSimpleFalse)
if (TII->ReverseBranchCondition(Cond))
assert(false && "Unable to reverse branch condition!");
// Initialize liveins to the first BB. These are potentiall redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(CvtBBI->BB, Redefs, TRI);
InitPredRedefs(NextBBI->BB, Redefs, TRI);
if (CvtBBI->BB->pred_size() > 1) {
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
// the entry block.
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
} else {
PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
// Merge converted block into entry block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
}
bool IterIfcvt = true;
if (!canFallThroughTo(BBI.BB, NextBBI->BB)) {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.HasFallThrough = false;
// Now ifcvt'd block will look like this:
// BB:
// ...
// t, f = cmp
// if t op
// b BBf
//
// We cannot further ifcvt this block because the unconditional branch
// will have to be predicated on the new condition, that will not be
// available if cmp executes.
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (!IterIfcvt)
BBI.IsDone = true;
InvalidatePreds(BBI.BB);
CvtBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
DebugLoc dl; // FIXME: this is nowhere
SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end());
if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
std::swap(CvtBBI, NextBBI);
if (CvtBBI->IsDone ||
(CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) {
// Something has changed. It's no longer safe to predicate this block.
BBI.IsAnalyzed = false;
CvtBBI->IsAnalyzed = false;
return false;
}
if (Kind == ICTriangleFalse || Kind == ICTriangleFRev)
if (TII->ReverseBranchCondition(Cond))
assert(false && "Unable to reverse branch condition!");
if (Kind == ICTriangleRev || Kind == ICTriangleFRev) {
if (ReverseBranchCondition(*CvtBBI)) {
// BB has been changed, modify its predecessors (except for this
// one) so they don't get ifcvt'ed based on bad intel.
for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(),
E = CvtBBI->BB->pred_end(); PI != E; ++PI) {
MachineBasicBlock *PBB = *PI;
if (PBB == BBI.BB)
continue;
BBInfo &PBBI = BBAnalysis[PBB->getNumber()];
if (PBBI.IsEnqueued) {
PBBI.IsAnalyzed = false;
PBBI.IsEnqueued = false;
}
}
}
}
// Initialize liveins to the first BB. These are potentially redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(CvtBBI->BB, Redefs, TRI);
InitPredRedefs(NextBBI->BB, Redefs, TRI);
bool HasEarlyExit = CvtBBI->FalseBB != NULL;
if (CvtBBI->BB->pred_size() > 1) {
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
// the entry block.
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
} else {
// Predicate the 'true' block after removing its branch.
CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB);
PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
// Now merge the entry of the triangle with the true block.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI, false);
}
// If 'true' block has a 'false' successor, add an exit branch to it.
if (HasEarlyExit) {
SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(),
CvtBBI->BrCond.end());
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond, dl);
BBI.BB->addSuccessor(CvtBBI->FalseBB);
}
// Merge in the 'false' block if the 'false' block has no other
// predecessors. Otherwise, add an unconditional branch to 'false'.
bool FalseBBDead = false;
bool IterIfcvt = true;
bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB);
if (!isFallThrough) {
// Only merge them if the true block does not fallthrough to the false
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
if (!HasEarlyExit &&
NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) {
MergeBlocks(BBI, *NextBBI);
FalseBBDead = true;
} else {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.HasFallThrough = false;
}
// Mixed predicated and unpredicated code. This cannot be iteratively
// predicated.
IterIfcvt = false;
}
RemoveExtraEdges(BBI);
// Update block info. BB can be iteratively if-converted.
if (!IterIfcvt)
BBI.IsDone = true;
InvalidatePreds(BBI.BB);
CvtBBI->IsDone = true;
if (FalseBBDead)
NextBBI->IsDone = true;
// FIXME: Must maintain LiveIns.
return true;
}
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
unsigned NumDups1, unsigned NumDups2) {
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
MachineBasicBlock *TailBB = TrueBBI.TrueBB;
// True block must fall through or end with an unanalyzable terminator.
if (!TailBB) {
if (blockAlwaysFallThrough(TrueBBI))
TailBB = FalseBBI.TrueBB;
assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!");
}
if (TrueBBI.IsDone || FalseBBI.IsDone ||
TrueBBI.BB->pred_size() > 1 ||
FalseBBI.BB->pred_size() > 1) {
// Something has changed. It's no longer safe to predicate these blocks.
BBI.IsAnalyzed = false;
TrueBBI.IsAnalyzed = false;
FalseBBI.IsAnalyzed = false;
return false;
}
// Put the predicated instructions from the 'true' block before the
// instructions from the 'false' block, unless the true block would clobber
// the predicate, in which case, do the opposite.
BBInfo *BBI1 = &TrueBBI;
BBInfo *BBI2 = &FalseBBI;
SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
if (TII->ReverseBranchCondition(RevCond))
assert(false && "Unable to reverse branch condition!");
SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond;
SmallVector<MachineOperand, 4> *Cond2 = &RevCond;
// Figure out the more profitable ordering.
bool DoSwap = false;
if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred)
DoSwap = true;
else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) {
if (TrueBBI.NonPredSize > FalseBBI.NonPredSize)
DoSwap = true;
}
if (DoSwap) {
std::swap(BBI1, BBI2);
std::swap(Cond1, Cond2);
}
// Remove the conditional branch from entry to the blocks.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Initialize liveins to the first BB. These are potentially redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(BBI1->BB, Redefs, TRI);
// Remove the duplicated instructions at the beginnings of both paths.
MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
MachineBasicBlock::iterator DI2 = BBI2->BB->begin();
MachineBasicBlock::iterator DIE1 = BBI1->BB->end();
MachineBasicBlock::iterator DIE2 = BBI2->BB->end();
// Skip dbg_value instructions
while (DI1 != DIE1 && DI1->isDebugValue())
++DI1;
while (DI2 != DIE2 && DI2->isDebugValue())
++DI2;
BBI1->NonPredSize -= NumDups1;
BBI2->NonPredSize -= NumDups1;
// Skip past the dups on each side separately since there may be
// differing dbg_value entries.
for (unsigned i = 0; i < NumDups1; ++DI1) {
if (!DI1->isDebugValue())
++i;
}
while (NumDups1 != 0) {
++DI2;
if (!DI2->isDebugValue())
--NumDups1;
}
UpdatePredRedefs(BBI1->BB->begin(), DI1, Redefs, TRI);
BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
BBI2->BB->erase(BBI2->BB->begin(), DI2);
// Predicate the 'true' block after removing its branch.
BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB);
DI1 = BBI1->BB->end();
for (unsigned i = 0; i != NumDups2; ) {
// NumDups2 only counted non-dbg_value instructions, so this won't
// run off the head of the list.
assert (DI1 != BBI1->BB->begin());
--DI1;
// skip dbg_value instructions
if (!DI1->isDebugValue())
++i;
}
BBI1->BB->erase(DI1, BBI1->BB->end());
PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1, Redefs);
// Predicate the 'false' block.
BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
DI2 = BBI2->BB->end();
while (NumDups2 != 0) {
// NumDups2 only counted non-dbg_value instructions, so this won't
// run off the head of the list.
assert (DI2 != BBI2->BB->begin());
--DI2;
// skip dbg_value instructions
if (!DI2->isDebugValue())
--NumDups2;
}
PredicateBlock(*BBI2, DI2, *Cond2, Redefs);
// Merge the true block into the entry of the diamond.
MergeBlocks(BBI, *BBI1, TailBB == 0);
MergeBlocks(BBI, *BBI2, TailBB == 0);
// If the if-converted block falls through or unconditionally branches into
// the tail block, and the tail block does not have other predecessors, then
// fold the tail block in as well. Otherwise, unless it falls through to the
// tail, add a unconditional branch to it.
if (TailBB) {
BBInfo TailBBI = BBAnalysis[TailBB->getNumber()];
bool CanMergeTail = !TailBBI.HasFallThrough;
// There may still be a fall-through edge from BBI1 or BBI2 to TailBB;
// check if there are any other predecessors besides those.
unsigned NumPreds = TailBB->pred_size();
if (NumPreds > 1)
CanMergeTail = false;
else if (NumPreds == 1 && CanMergeTail) {
MachineBasicBlock::pred_iterator PI = TailBB->pred_begin();
if (*PI != BBI1->BB && *PI != BBI2->BB)
CanMergeTail = false;
}
if (CanMergeTail) {
MergeBlocks(BBI, TailBBI);
TailBBI.IsDone = true;
} else {
BBI.BB->addSuccessor(TailBB);
InsertUncondBranch(BBI.BB, TailBB, TII);
BBI.HasFallThrough = false;
}
}
// RemoveExtraEdges won't work if the block has an unanalyzable branch,
// which can happen here if TailBB is unanalyzable and is merged, so
// explicitly remove BBI1 and BBI2 as successors.
BBI.BB->removeSuccessor(BBI1->BB);
BBI.BB->removeSuccessor(BBI2->BB);
RemoveExtraEdges(BBI);
// Update block info.
BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true;
InvalidatePreds(BBI.BB);
// FIXME: Must maintain LiveIns.
return true;
}
/// PredicateBlock - Predicate instructions from the start of the block to the
/// specified end with the specified condition.
void IfConverter::PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs) {
for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) {
if (I->isDebugValue() || TII->isPredicated(I))
continue;
if (!TII->PredicateInstruction(I, Cond)) {
#ifndef NDEBUG
dbgs() << "Unable to predicate " << *I << "!\n";
#endif
llvm_unreachable(0);
}
// If the predicated instruction now redefines a register as the result of
// if-conversion, add an implicit kill.
UpdatePredRedefs(I, Redefs, TRI, true);
}
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
BBI.IsAnalyzed = false;
BBI.NonPredSize = 0;
++NumIfConvBBs;
}
/// CopyAndPredicateBlock - Copy and predicate instructions from source BB to
/// the destination block. Skip end of block branches if IgnoreBr is true.
void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
bool IgnoreBr) {
MachineFunction &MF = *ToBBI.BB->getParent();
for (MachineBasicBlock::iterator I = FromBBI.BB->begin(),
E = FromBBI.BB->end(); I != E; ++I) {
const TargetInstrDesc &TID = I->getDesc();
// Do not copy the end of the block branches.
if (IgnoreBr && TID.isBranch())
break;
MachineInstr *MI = MF.CloneMachineInstr(I);
ToBBI.BB->insert(ToBBI.BB->end(), MI);
ToBBI.NonPredSize++;
unsigned ExtraPredCost = 0;
unsigned NumCycles = TII->getInstrLatency(InstrItins, &*I, &ExtraPredCost);
if (NumCycles > 1)
ToBBI.ExtraCost += NumCycles-1;
ToBBI.ExtraCost2 += ExtraPredCost;
if (!TII->isPredicated(I) && !MI->isDebugValue()) {
if (!TII->PredicateInstruction(MI, Cond)) {
#ifndef NDEBUG
dbgs() << "Unable to predicate " << *I << "!\n";
#endif
llvm_unreachable(0);
}
}
// If the predicated instruction now redefines a register as the result of
// if-conversion, add an implicit kill.
UpdatePredRedefs(MI, Redefs, TRI, true);
}
if (!IgnoreBr) {
std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
FromBBI.BB->succ_end());
MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
// Fallthrough edge can't be transferred.
if (Succ == FallThrough)
continue;
ToBBI.BB->addSuccessor(Succ);
}
}
std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
std::back_inserter(ToBBI.Predicate));
std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate));
ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
ToBBI.IsAnalyzed = false;
++NumDupBBs;
}
/// MergeBlocks - Move all instructions from FromBB to the end of ToBB.
/// This will leave FromBB as an empty block, so remove all of its
/// successor edges except for the fall-through edge. If AddEdges is true,
/// i.e., when FromBBI's branch is being moved, add those successor edges to
/// ToBBI.
void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) {
ToBBI.BB->splice(ToBBI.BB->end(),
FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end());
std::vector<MachineBasicBlock *> Succs(FromBBI.BB->succ_begin(),
FromBBI.BB->succ_end());
MachineBasicBlock *NBB = getNextBlock(FromBBI.BB);
MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL;
for (unsigned i = 0, e = Succs.size(); i != e; ++i) {
MachineBasicBlock *Succ = Succs[i];
// Fallthrough edge can't be transferred.
if (Succ == FallThrough)
continue;
FromBBI.BB->removeSuccessor(Succ);
if (AddEdges)
ToBBI.BB->addSuccessor(Succ);
}
// Now FromBBI always falls through to the next block!
if (NBB && !FromBBI.BB->isSuccessor(NBB))
FromBBI.BB->addSuccessor(NBB);
std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(),
std::back_inserter(ToBBI.Predicate));
FromBBI.Predicate.clear();
ToBBI.NonPredSize += FromBBI.NonPredSize;
ToBBI.ExtraCost += FromBBI.ExtraCost;
ToBBI.ExtraCost2 += FromBBI.ExtraCost2;
FromBBI.NonPredSize = 0;
FromBBI.ExtraCost = 0;
FromBBI.ExtraCost2 = 0;
ToBBI.ClobbersPred |= FromBBI.ClobbersPred;
ToBBI.HasFallThrough = FromBBI.HasFallThrough;
ToBBI.IsAnalyzed = false;
FromBBI.IsAnalyzed = false;
}
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