mirror of
https://github.com/RPCS3/llvm.git
synced 2024-12-17 17:06:59 +00:00
5560c9d49c
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7944 91177308-0d34-0410-b5e6-96231b3b80d8
332 lines
14 KiB
C++
332 lines
14 KiB
C++
//===- LoadValueNumbering.cpp - Load Value #'ing Implementation -*- C++ -*-===//
|
|
//
|
|
// This file implements a value numbering pass that value #'s load instructions.
|
|
// To do this, it finds lexically identical load instructions, and uses alias
|
|
// analysis to determine which loads are guaranteed to produce the same value.
|
|
//
|
|
// This pass builds off of another value numbering pass to implement value
|
|
// numbering for non-load instructions. It uses Alias Analysis so that it can
|
|
// disambiguate the load instructions. The more powerful these base analyses
|
|
// are, the more powerful the resultant analysis will be.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Analysis/LoadValueNumbering.h"
|
|
#include "llvm/Analysis/ValueNumbering.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Target/TargetData.h"
|
|
#include "llvm/Pass.h"
|
|
#include "llvm/Type.h"
|
|
#include "llvm/iMemory.h"
|
|
#include "llvm/BasicBlock.h"
|
|
#include "llvm/Support/CFG.h"
|
|
#include <algorithm>
|
|
#include <set>
|
|
|
|
namespace {
|
|
// FIXME: This should not be a FunctionPass.
|
|
struct LoadVN : public FunctionPass, public ValueNumbering {
|
|
|
|
/// Pass Implementation stuff. This doesn't do any analysis.
|
|
///
|
|
bool runOnFunction(Function &) { return false; }
|
|
|
|
/// getAnalysisUsage - Does not modify anything. It uses Value Numbering
|
|
/// and Alias Analysis.
|
|
///
|
|
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
|
|
|
|
/// getEqualNumberNodes - Return nodes with the same value number as the
|
|
/// specified Value. This fills in the argument vector with any equal
|
|
/// values.
|
|
///
|
|
virtual void getEqualNumberNodes(Value *V1,
|
|
std::vector<Value*> &RetVals) const;
|
|
private:
|
|
/// haveEqualValueNumber - Given two load instructions, determine if they
|
|
/// both produce the same value on every execution of the program, assuming
|
|
/// that their source operands always give the same value. This uses the
|
|
/// AliasAnalysis implementation to invalidate loads when stores or function
|
|
/// calls occur that could modify the value produced by the load.
|
|
///
|
|
bool haveEqualValueNumber(LoadInst *LI, LoadInst *LI2, AliasAnalysis &AA,
|
|
DominatorSet &DomSetInfo) const;
|
|
bool haveEqualValueNumber(LoadInst *LI, StoreInst *SI, AliasAnalysis &AA,
|
|
DominatorSet &DomSetInfo) const;
|
|
};
|
|
|
|
// Register this pass...
|
|
RegisterOpt<LoadVN> X("load-vn", "Load Value Numbering");
|
|
|
|
// Declare that we implement the ValueNumbering interface
|
|
RegisterAnalysisGroup<ValueNumbering, LoadVN> Y;
|
|
}
|
|
|
|
|
|
|
|
Pass *createLoadValueNumberingPass() { return new LoadVN(); }
|
|
|
|
|
|
/// getAnalysisUsage - Does not modify anything. It uses Value Numbering and
|
|
/// Alias Analysis.
|
|
///
|
|
void LoadVN::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesAll();
|
|
AU.addRequired<AliasAnalysis>();
|
|
AU.addRequired<ValueNumbering>();
|
|
AU.addRequired<DominatorSet>();
|
|
AU.addRequired<TargetData>();
|
|
}
|
|
|
|
// getEqualNumberNodes - Return nodes with the same value number as the
|
|
// specified Value. This fills in the argument vector with any equal values.
|
|
//
|
|
void LoadVN::getEqualNumberNodes(Value *V,
|
|
std::vector<Value*> &RetVals) const {
|
|
// If the alias analysis has any must alias information to share with us, we
|
|
// can definately use it.
|
|
if (isa<PointerType>(V->getType()))
|
|
getAnalysis<AliasAnalysis>().getMustAliases(V, RetVals);
|
|
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
|
|
// If we have a load instruction, find all of the load and store
|
|
// instructions that use the same source operand. We implement this
|
|
// recursively, because there could be a load of a load of a load that are
|
|
// all identical. We are guaranteed that this cannot be an infinite
|
|
// recursion because load instructions would have to pass through a PHI node
|
|
// in order for there to be a cycle. The PHI node would be handled by the
|
|
// else case here, breaking the infinite recursion.
|
|
//
|
|
std::vector<Value*> PointerSources;
|
|
getEqualNumberNodes(LI->getOperand(0), PointerSources);
|
|
PointerSources.push_back(LI->getOperand(0));
|
|
|
|
Function *F = LI->getParent()->getParent();
|
|
|
|
// Now that we know the set of equivalent source pointers for the load
|
|
// instruction, look to see if there are any load or store candiates that
|
|
// are identical.
|
|
//
|
|
std::vector<LoadInst*> CandidateLoads;
|
|
std::vector<StoreInst*> CandidateStores;
|
|
|
|
while (!PointerSources.empty()) {
|
|
Value *Source = PointerSources.back();
|
|
PointerSources.pop_back(); // Get a source pointer...
|
|
|
|
for (Value::use_iterator UI = Source->use_begin(), UE = Source->use_end();
|
|
UI != UE; ++UI)
|
|
if (LoadInst *Cand = dyn_cast<LoadInst>(*UI)) {// Is a load of source?
|
|
if (Cand->getParent()->getParent() == F && // In the same function?
|
|
Cand != LI) // Not LI itself?
|
|
CandidateLoads.push_back(Cand); // Got one...
|
|
} else if (StoreInst *Cand = dyn_cast<StoreInst>(*UI)) {
|
|
if (Cand->getParent()->getParent() == F &&
|
|
Cand->getOperand(1) == Source) // It's a store THROUGH the ptr...
|
|
CandidateStores.push_back(Cand);
|
|
}
|
|
}
|
|
|
|
// Remove duplicates from the CandidateLoads list because alias analysis
|
|
// processing may be somewhat expensive and we don't want to do more work
|
|
// than necessary.
|
|
//
|
|
unsigned OldSize = CandidateLoads.size();
|
|
std::sort(CandidateLoads.begin(), CandidateLoads.end());
|
|
CandidateLoads.erase(std::unique(CandidateLoads.begin(),
|
|
CandidateLoads.end()),
|
|
CandidateLoads.end());
|
|
// FIXME: REMOVE THIS SORTING AND UNIQUING IF IT CAN'T HAPPEN
|
|
assert(CandidateLoads.size() == OldSize && "Shrunk the candloads list?");
|
|
|
|
// Get Alias Analysis...
|
|
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
|
|
DominatorSet &DomSetInfo = getAnalysis<DominatorSet>();
|
|
|
|
// Loop over all of the candindate loads. If they are not invalidated by
|
|
// stores or calls between execution of them and LI, then add them to
|
|
// RetVals.
|
|
for (unsigned i = 0, e = CandidateLoads.size(); i != e; ++i)
|
|
if (haveEqualValueNumber(LI, CandidateLoads[i], AA, DomSetInfo))
|
|
RetVals.push_back(CandidateLoads[i]);
|
|
for (unsigned i = 0, e = CandidateStores.size(); i != e; ++i)
|
|
if (haveEqualValueNumber(LI, CandidateStores[i], AA, DomSetInfo))
|
|
RetVals.push_back(CandidateStores[i]->getOperand(0));
|
|
|
|
} else {
|
|
assert(&getAnalysis<ValueNumbering>() != (ValueNumbering*)this &&
|
|
"getAnalysis() returned this!");
|
|
|
|
// Not a load instruction? Just chain to the base value numbering
|
|
// implementation to satisfy the request...
|
|
return getAnalysis<ValueNumbering>().getEqualNumberNodes(V, RetVals);
|
|
}
|
|
}
|
|
|
|
// CheckForInvalidatingInst - Return true if BB or any of the predecessors of BB
|
|
// (until DestBB) contain an instruction that might invalidate Ptr.
|
|
//
|
|
static bool CheckForInvalidatingInst(BasicBlock *BB, BasicBlock *DestBB,
|
|
Value *Ptr, unsigned Size,
|
|
AliasAnalysis &AA,
|
|
std::set<BasicBlock*> &VisitedSet) {
|
|
// Found the termination point!
|
|
if (BB == DestBB || VisitedSet.count(BB)) return false;
|
|
|
|
// Avoid infinite recursion!
|
|
VisitedSet.insert(BB);
|
|
|
|
// Can this basic block modify Ptr?
|
|
if (AA.canBasicBlockModify(*BB, Ptr, Size))
|
|
return true;
|
|
|
|
// Check all of our predecessor blocks...
|
|
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI)
|
|
if (CheckForInvalidatingInst(*PI, DestBB, Ptr, Size, AA, VisitedSet))
|
|
return true;
|
|
|
|
// None of our predecessor blocks contain an invalidating instruction, and we
|
|
// don't either!
|
|
return false;
|
|
}
|
|
|
|
|
|
/// haveEqualValueNumber - Given two load instructions, determine if they both
|
|
/// produce the same value on every execution of the program, assuming that
|
|
/// their source operands always give the same value. This uses the
|
|
/// AliasAnalysis implementation to invalidate loads when stores or function
|
|
/// calls occur that could modify the value produced by the load.
|
|
///
|
|
bool LoadVN::haveEqualValueNumber(LoadInst *L1, LoadInst *L2,
|
|
AliasAnalysis &AA,
|
|
DominatorSet &DomSetInfo) const {
|
|
// Figure out which load dominates the other one. If neither dominates the
|
|
// other we cannot eliminate them.
|
|
//
|
|
// FIXME: This could be enhanced to some cases with a shared dominator!
|
|
//
|
|
if (DomSetInfo.dominates(L2, L1))
|
|
std::swap(L1, L2); // Make L1 dominate L2
|
|
else if (!DomSetInfo.dominates(L1, L2))
|
|
return false; // Neither instruction dominates the other one...
|
|
|
|
BasicBlock *BB1 = L1->getParent(), *BB2 = L2->getParent();
|
|
Value *LoadAddress = L1->getOperand(0);
|
|
|
|
assert(L1->getType() == L2->getType() &&
|
|
"How could the same source pointer return different types?");
|
|
|
|
// Find out how many bytes of memory are loaded by the load instruction...
|
|
unsigned LoadSize = getAnalysis<TargetData>().getTypeSize(L1->getType());
|
|
|
|
// L1 now dominates L2. Check to see if the intervening instructions between
|
|
// the two loads include a store or call...
|
|
//
|
|
if (BB1 == BB2) { // In same basic block?
|
|
// In this degenerate case, no checking of global basic blocks has to occur
|
|
// just check the instructions BETWEEN L1 & L2...
|
|
//
|
|
if (AA.canInstructionRangeModify(*L1, *L2, LoadAddress, LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// No instructions invalidate the loads, they produce the same value!
|
|
return true;
|
|
} else {
|
|
// Make sure that there are no store instructions between L1 and the end of
|
|
// its basic block...
|
|
//
|
|
if (AA.canInstructionRangeModify(*L1, *BB1->getTerminator(), LoadAddress,
|
|
LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// Make sure that there are no store instructions between the start of BB2
|
|
// and the second load instruction...
|
|
//
|
|
if (AA.canInstructionRangeModify(BB2->front(), *L2, LoadAddress, LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// Do a depth first traversal of the inverse CFG starting at L2's block,
|
|
// looking for L1's block. The inverse CFG is made up of the predecessor
|
|
// nodes of a block... so all of the edges in the graph are "backward".
|
|
//
|
|
std::set<BasicBlock*> VisitedSet;
|
|
for (pred_iterator PI = pred_begin(BB2), PE = pred_end(BB2); PI != PE; ++PI)
|
|
if (CheckForInvalidatingInst(*PI, BB1, LoadAddress, LoadSize, AA,
|
|
VisitedSet))
|
|
return false;
|
|
|
|
// If we passed all of these checks then we are sure that the two loads
|
|
// produce the same value.
|
|
return true;
|
|
}
|
|
}
|
|
|
|
|
|
/// haveEqualValueNumber - Given a load instruction and a store instruction,
|
|
/// determine if the stored value reaches the loaded value unambiguously on
|
|
/// every execution of the program. This uses the AliasAnalysis implementation
|
|
/// to invalidate the stored value when stores or function calls occur that
|
|
/// could modify the value produced by the load.
|
|
///
|
|
bool LoadVN::haveEqualValueNumber(LoadInst *Load, StoreInst *Store,
|
|
AliasAnalysis &AA,
|
|
DominatorSet &DomSetInfo) const {
|
|
// If the store does not dominate the load, we cannot do anything...
|
|
if (!DomSetInfo.dominates(Store, Load))
|
|
return false;
|
|
|
|
BasicBlock *BB1 = Store->getParent(), *BB2 = Load->getParent();
|
|
Value *LoadAddress = Load->getOperand(0);
|
|
|
|
assert(LoadAddress->getType() == Store->getOperand(1)->getType() &&
|
|
"How could the same source pointer return different types?");
|
|
|
|
// Find out how many bytes of memory are loaded by the load instruction...
|
|
unsigned LoadSize = getAnalysis<TargetData>().getTypeSize(Load->getType());
|
|
|
|
// Compute a basic block iterator pointing to the instruction after the store.
|
|
BasicBlock::iterator StoreIt = Store; ++StoreIt;
|
|
|
|
// Check to see if the intervening instructions between the two store and load
|
|
// include a store or call...
|
|
//
|
|
if (BB1 == BB2) { // In same basic block?
|
|
// In this degenerate case, no checking of global basic blocks has to occur
|
|
// just check the instructions BETWEEN Store & Load...
|
|
//
|
|
if (AA.canInstructionRangeModify(*StoreIt, *Load, LoadAddress, LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// No instructions invalidate the stored value, they produce the same value!
|
|
return true;
|
|
} else {
|
|
// Make sure that there are no store instructions between the Store and the
|
|
// end of its basic block...
|
|
//
|
|
if (AA.canInstructionRangeModify(*StoreIt, *BB1->getTerminator(),
|
|
LoadAddress, LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// Make sure that there are no store instructions between the start of BB2
|
|
// and the second load instruction...
|
|
//
|
|
if (AA.canInstructionRangeModify(BB2->front(), *Load, LoadAddress,LoadSize))
|
|
return false; // Cannot eliminate load
|
|
|
|
// Do a depth first traversal of the inverse CFG starting at L2's block,
|
|
// looking for L1's block. The inverse CFG is made up of the predecessor
|
|
// nodes of a block... so all of the edges in the graph are "backward".
|
|
//
|
|
std::set<BasicBlock*> VisitedSet;
|
|
for (pred_iterator PI = pred_begin(BB2), PE = pred_end(BB2); PI != PE; ++PI)
|
|
if (CheckForInvalidatingInst(*PI, BB1, LoadAddress, LoadSize, AA,
|
|
VisitedSet))
|
|
return false;
|
|
|
|
// If we passed all of these checks then we are sure that the two loads
|
|
// produce the same value.
|
|
return true;
|
|
}
|
|
}
|