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Mark MergedLoadStoreMotion as not preserving MemDep results

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Summary:
MemDep caches results that signify that a dependence is non-local, and
there is currently no way to invalidate such cache entries.
Unfortunately, when MLSM sinks a store that can result in a non-local
dependence becoming a local one, and then MemDep gives wrong answers.
The easiest way out here is to just say that MLSM does indeed not
preserve MemDep results.

Reviewers: davide, Gerolf

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D43177

llvm-svn: 325880
This commit is contained in:
Bjorn Steinbrink 2018-02-23 10:41:57 +00:00
parent 8c1fff475e
commit 4b19fcab9c
2 changed files with 30 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
lib/Transforms/Scalar/MergedLoadStoreMotion.cpp
View File

@ -80,7 +80,6 @@
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/MemoryDependenceAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Metadata.h"
#include "llvm/Support/Debug.h"
@ -97,7 +96,6 @@ namespace {
// MergedLoadStoreMotion Pass
//===----------------------------------------------------------------------===//
class MergedLoadStoreMotion {
MemoryDependenceResults *MD = nullptr;
AliasAnalysis *AA = nullptr;
// The mergeLoad/Store algorithms could have Size0 * Size1 complexity,
@ -107,14 +105,9 @@ class MergedLoadStoreMotion {
const int MagicCompileTimeControl = 250;
public:
bool run(Function &F, MemoryDependenceResults *MD, AliasAnalysis &AA);
bool run(Function &F, AliasAnalysis &AA);
private:
///
/// \brief Remove instruction from parent and update memory dependence
/// analysis.
///
void removeInstruction(Instruction *Inst);
BasicBlock *getDiamondTail(BasicBlock *BB);
bool isDiamondHead(BasicBlock *BB);
// Routines for sinking stores
@ -127,22 +120,6 @@ private:
};
} // end anonymous namespace
///
/// \brief Remove instruction from parent and update memory dependence analysis.
///
void MergedLoadStoreMotion::removeInstruction(Instruction *Inst) {
// Notify the memory dependence analysis.
if (MD) {
MD->removeInstruction(Inst);
if (auto *LI = dyn_cast<LoadInst>(Inst))
MD->invalidateCachedPointerInfo(LI->getPointerOperand());
if (Inst->getType()->isPtrOrPtrVectorTy()) {
MD->invalidateCachedPointerInfo(Inst);
}
}
Inst->eraseFromParent();
}
///
/// \brief Return tail block of a diamond.
///
@ -236,8 +213,6 @@ PHINode *MergedLoadStoreMotion::getPHIOperand(BasicBlock *BB, StoreInst *S0,
&BB->front());
NewPN->addIncoming(Opd1, S0->getParent());
NewPN->addIncoming(Opd2, S1->getParent());
if (MD && NewPN->getType()->isPtrOrPtrVectorTy())
MD->invalidateCachedPointerInfo(NewPN);
return NewPN;
}
@ -275,12 +250,12 @@ bool MergedLoadStoreMotion::sinkStore(BasicBlock *BB, StoreInst *S0,
// New PHI operand? Use it.
if (PHINode *NewPN = getPHIOperand(BB, S0, S1))
SNew->setOperand(0, NewPN);
removeInstruction(S0);
removeInstruction(S1);
S0->eraseFromParent();
S1->eraseFromParent();
A0->replaceAllUsesWith(ANew);
removeInstruction(A0);
A0->eraseFromParent();
A1->replaceAllUsesWith(ANew);
removeInstruction(A1);
A1->eraseFromParent();
return true;
}
return false;
@ -344,9 +319,7 @@ bool MergedLoadStoreMotion::mergeStores(BasicBlock *T) {
return MergedStores;
}
bool MergedLoadStoreMotion::run(Function &F, MemoryDependenceResults *MD,
AliasAnalysis &AA) {
this->MD = MD;
bool MergedLoadStoreMotion::run(Function &F, AliasAnalysis &AA) {
this->AA = &AA;
bool Changed = false;
@ -382,9 +355,7 @@ public:
if (skipFunction(F))
return false;
MergedLoadStoreMotion Impl;
auto *MDWP = getAnalysisIfAvailable<MemoryDependenceWrapperPass>();
return Impl.run(F, MDWP ? &MDWP->getMemDep() : nullptr,
getAnalysis<AAResultsWrapperPass>().getAAResults());
return Impl.run(F, getAnalysis<AAResultsWrapperPass>().getAAResults());
}
private:
@ -392,7 +363,6 @@ private:
AU.setPreservesCFG();
AU.addRequired<AAResultsWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<MemoryDependenceWrapperPass>();
}
};
@ -408,7 +378,6 @@ FunctionPass *llvm::createMergedLoadStoreMotionPass() {
INITIALIZE_PASS_BEGIN(MergedLoadStoreMotionLegacyPass, "mldst-motion",
"MergedLoadStoreMotion", false, false)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(MergedLoadStoreMotionLegacyPass, "mldst-motion",
"MergedLoadStoreMotion", false, false)
@ -416,14 +385,12 @@ INITIALIZE_PASS_END(MergedLoadStoreMotionLegacyPass, "mldst-motion",
PreservedAnalyses
MergedLoadStoreMotionPass::run(Function &F, FunctionAnalysisManager &AM) {
MergedLoadStoreMotion Impl;
auto *MD = AM.getCachedResult<MemoryDependenceAnalysis>(F);
auto &AA = AM.getResult<AAManager>(F);
if (!Impl.run(F, MD, AA))
if (!Impl.run(F, AA))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<GlobalsAA>();
PA.preserve<MemoryDependenceAnalysis>();
return PA;
}

22
test/Transforms/GVN/pr36063.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: opt < %s -memcpyopt -mldst-motion -gvn -S | FileCheck %s
define void @foo(i8* %ret, i1 %x) {
%a = alloca i8
br i1 %x, label %yes, label %no
yes: ; preds = %0
%gepa = getelementptr i8, i8* %a, i64 0
store i8 5, i8* %gepa
br label %out
no: ; preds = %0
%gepb = getelementptr i8, i8* %a, i64 0
store i8 5, i8* %gepb
br label %out
out: ; preds = %no, %yes
%tmp = load i8, i8* %a
; CHECK-NOT: undef
store i8 %tmp, i8* %ret
ret void
}