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[PM] Port DSE to the new pass manager 

Patch by JakeVanAdrighem. Thanks!

llvm-svn: 269847
This commit is contained in:
Justin Bogner 2016-05-17 21:38:13 +00:00
parent 622a9394f9
commit 594e07bd78
7 changed files with 446 additions and 391 deletions
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2
llvm/include/llvm/InitializePasses.h
View File

@ -105,7 +105,7 @@ void initializeCrossDSOCFIPass(PassRegistry&);
void initializeDAEPass(PassRegistry&);
void initializeDAHPass(PassRegistry&);
void initializeDCELegacyPassPass(PassRegistry&);
void initializeDSEPass(PassRegistry&);
void initializeDSELegacyPassPass(PassRegistry&);
void initializeDeadInstEliminationPass(PassRegistry&);
void initializeDeadMachineInstructionElimPass(PassRegistry&);
void initializeDelinearizationPass(PassRegistry &);

34
llvm/include/llvm/Transforms/Scalar/DeadStoreElimination.h Normal file
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@ -0,0 +1,34 @@
//===- DeadStoreElimination.h - Fast Dead Store Elimination -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a trivial dead store elimination that only considers
// basic-block local redundant stores.
//
// FIXME: This should eventually be extended to be a post-dominator tree
// traversal. Doing so would be pretty trivial.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_DSE_H
#define LLVM_TRANSFORMS_SCALAR_DSE_H
#include "llvm/IR/Function.h"
#include "llvm/IR/PassManager.h"
namespace llvm {
/// This class implements a trivial dead store elimination. We consider
/// only the redundant stores that are local to a single Basic Block.
class DSEPass : public PassInfoMixin<DSEPass> {
public:
PreservedAnalyses run(Function &F, AnalysisManager<Function> &FAM);
};
}
#endif // LLVM_TRANSFORMS_SCALAR_DSE_H

1
llvm/lib/Passes/PassBuilder.cpp
View File

@ -64,6 +64,7 @@
#include "llvm/Transforms/PGOInstrumentation.h"
#include "llvm/Transforms/Scalar/ADCE.h"
#include "llvm/Transforms/Scalar/DCE.h"
#include "llvm/Transforms/Scalar/DeadStoreElimination.h"
#include "llvm/Transforms/Scalar/EarlyCSE.h"
#include "llvm/Transforms/Scalar/GVN.h"
#include "llvm/Transforms/Scalar/LoopRotation.h"

1
llvm/lib/Passes/PassRegistry.def
View File

@ -111,6 +111,7 @@ FUNCTION_ALIAS_ANALYSIS("type-based-aa", TypeBasedAA())
FUNCTION_PASS("aa-eval", AAEvaluator())
FUNCTION_PASS("adce", ADCEPass())
FUNCTION_PASS("dce", DCEPass())
FUNCTION_PASS("dse", DSEPass())
FUNCTION_PASS("early-cse", EarlyCSEPass())
FUNCTION_PASS("instcombine", InstCombinePass())
FUNCTION_PASS("invalidate<all>", InvalidateAllAnalysesPass())

796
llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
View File

@ -15,7 +15,7 @@
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/DeadStoreElimination.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
@ -36,6 +36,7 @@
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
@ -45,84 +46,19 @@ STATISTIC(NumRedundantStores, "Number of redundant stores deleted");
STATISTIC(NumFastStores, "Number of stores deleted");
STATISTIC(NumFastOther , "Number of other instrs removed");
namespace {
struct DSE : public FunctionPass {
AliasAnalysis *AA;
MemoryDependenceResults *MD;
DominatorTree *DT;
const TargetLibraryInfo *TLI;
static char ID; // Pass identification, replacement for typeid
DSE() : FunctionPass(ID), AA(nullptr), MD(nullptr), DT(nullptr) {
initializeDSEPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
MD = &getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
bool Changed = false;
for (BasicBlock &I : F)
// Only check non-dead blocks. Dead blocks may have strange pointer
// cycles that will confuse alias analysis.
if (DT->isReachableFromEntry(&I))
Changed |= runOnBasicBlock(I);
AA = nullptr; MD = nullptr; DT = nullptr;
return Changed;
}
bool runOnBasicBlock(BasicBlock &BB);
bool MemoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI);
bool HandleFree(CallInst *F);
bool handleEndBlock(BasicBlock &BB);
void RemoveAccessedObjects(const MemoryLocation &LoadedLoc,
SmallSetVector<Value *, 16> &DeadStackObjects,
const DataLayout &DL);
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<MemoryDependenceWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<MemoryDependenceWrapperPass>();
}
};
}
char DSE::ID = 0;
INITIALIZE_PASS_BEGIN(DSE, "dse", "Dead Store Elimination", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(DSE, "dse", "Dead Store Elimination", false, false)
FunctionPass *llvm::createDeadStoreEliminationPass() { return new DSE(); }
//===----------------------------------------------------------------------===//
// Helper functions
//===----------------------------------------------------------------------===//
/// DeleteDeadInstruction - Delete this instruction. Before we do, go through
/// and zero out all the operands of this instruction. If any of them become
/// dead, delete them and the computation tree that feeds them.
///
/// Delete this instruction. Before we do, go through and zero out all the
/// operands of this instruction. If any of them become dead, delete them and
/// the computation tree that feeds them.
/// If ValueSet is non-null, remove any deleted instructions from it as well.
///
static void DeleteDeadInstruction(Instruction *I,
MemoryDependenceResults &MD,
const TargetLibraryInfo &TLI,
SmallSetVector<Value*, 16> *ValueSet = nullptr) {
static void
deleteDeadInstruction(Instruction *I, MemoryDependenceResults &MD,
const TargetLibraryInfo &TLI,
SmallSetVector<Value *, 16> *ValueSet = nullptr) {
SmallVector<Instruction*, 32> NowDeadInsts;
NowDeadInsts.push_back(I);
@ -156,9 +92,8 @@ static void DeleteDeadInstruction(Instruction *I,
} while (!NowDeadInsts.empty());
}
/// hasMemoryWrite - Does this instruction write some memory? This only returns
/// true for things that we can analyze with other helpers below.
/// Does this instruction write some memory? This only returns true for things
/// that we can analyze with other helpers below.
static bool hasMemoryWrite(Instruction *I, const TargetLibraryInfo &TLI) {
if (isa<StoreInst>(I))
return true;
@ -197,9 +132,9 @@ static bool hasMemoryWrite(Instruction *I, const TargetLibraryInfo &TLI) {
return false;
}
/// getLocForWrite - Return a Location stored to by the specified instruction.
/// If isRemovable returns true, this function and getLocForRead completely
/// describe the memory operations for this instruction.
/// Return a Location stored to by the specified instruction. If isRemovable
/// returns true, this function and getLocForRead completely describe the memory
/// operations for this instruction.
static MemoryLocation getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
return MemoryLocation::get(SI);
@ -228,8 +163,8 @@ static MemoryLocation getLocForWrite(Instruction *Inst, AliasAnalysis &AA) {
}
}
/// getLocForRead - Return the location read by the specified "hasMemoryWrite"
/// instruction if any.
/// Return the location read by the specified "hasMemoryWrite" instruction if
/// any.
static MemoryLocation getLocForRead(Instruction *Inst,
const TargetLibraryInfo &TLI) {
assert(hasMemoryWrite(Inst, TLI) && "Unknown instruction case");
@ -241,9 +176,8 @@ static MemoryLocation getLocForRead(Instruction *Inst,
return MemoryLocation();
}
/// isRemovable - If the value of this instruction and the memory it writes to
/// is unused, may we delete this instruction?
/// If the value of this instruction and the memory it writes to is unused, may
/// we delete this instruction?
static bool isRemovable(Instruction *I) {
// Don't remove volatile/atomic stores.
if (StoreInst *SI = dyn_cast<StoreInst>(I))
@ -307,7 +241,7 @@ static bool isShortenableAtTheBeginning(Instruction *I) {
return II && II->getIntrinsicID() == Intrinsic::memset;
}
/// getStoredPointerOperand - Return the pointer that is being written to.
/// Return the pointer that is being written to.
static Value *getStoredPointerOperand(Instruction *I) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return SI->getPointerOperand();
@ -458,7 +392,7 @@ static OverwriteResult isOverwrite(const MemoryLocation &Later,
return OverwriteUnknown;
}
/// isPossibleSelfRead - If 'Inst' might be a self read (i.e. a noop copy of a
/// If 'Inst' might be a self read (i.e. a noop copy of a
/// memory region into an identical pointer) then it doesn't actually make its
/// input dead in the traditional sense. Consider this case:
///
@ -503,11 +437,317 @@ static bool isPossibleSelfRead(Instruction *Inst,
}
//===----------------------------------------------------------------------===//
// DSE Pass
//===----------------------------------------------------------------------===//
/// Returns true if the memory which is accessed by the second instruction is not
/// modified between the first and the second instruction.
/// Precondition: Second instruction must be dominated by the first
/// instruction.
static bool memoryIsNotModifiedBetween(Instruction *FirstI,
Instruction *SecondI,
AliasAnalysis *AA) {
SmallVector<BasicBlock *, 16> WorkList;
SmallPtrSet<BasicBlock *, 8> Visited;
BasicBlock::iterator FirstBBI(FirstI);
++FirstBBI;
BasicBlock::iterator SecondBBI(SecondI);
BasicBlock *FirstBB = FirstI->getParent();
BasicBlock *SecondBB = SecondI->getParent();
MemoryLocation MemLoc = MemoryLocation::get(SecondI);
bool DSE::runOnBasicBlock(BasicBlock &BB) {
// Start checking the store-block.
WorkList.push_back(SecondBB);
bool isFirstBlock = true;
// Check all blocks going backward until we reach the load-block.
while (!WorkList.empty()) {
BasicBlock *B = WorkList.pop_back_val();
// Ignore instructions before LI if this is the FirstBB.
BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
BasicBlock::iterator EI;
if (isFirstBlock) {
// Ignore instructions after SI if this is the first visit of SecondBB.
assert(B == SecondBB && "first block is not the store block");
EI = SecondBBI;
isFirstBlock = false;
} else {
// It's not SecondBB or (in case of a loop) the second visit of SecondBB.
// In this case we also have to look at instructions after SI.
EI = B->end();
}
for (; BI != EI; ++BI) {
Instruction *I = &*BI;
if (I->mayWriteToMemory() && I != SecondI) {
auto Res = AA->getModRefInfo(I, MemLoc);
if (Res != MRI_NoModRef)
return false;
}
}
if (B != FirstBB) {
assert(B != &FirstBB->getParent()->getEntryBlock() &&
"Should not hit the entry block because SI must be dominated by LI");
for (auto PredI = pred_begin(B), PE = pred_end(B); PredI != PE; ++PredI) {
if (!Visited.insert(*PredI).second)
continue;
WorkList.push_back(*PredI);
}
}
}
return true;
}
/// Find all blocks that will unconditionally lead to the block BB and append
/// them to F.
static void findUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
BasicBlock *BB, DominatorTree *DT) {
for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
BasicBlock *Pred = *I;
if (Pred == BB) continue;
TerminatorInst *PredTI = Pred->getTerminator();
if (PredTI->getNumSuccessors() != 1)
continue;
if (DT->isReachableFromEntry(Pred))
Blocks.push_back(Pred);
}
}
/// Handle frees of entire structures whose dependency is a store
/// to a field of that structure.
static bool handleFree(CallInst *F, AliasAnalysis *AA,
MemoryDependenceResults *MD, DominatorTree *DT,
const TargetLibraryInfo *TLI) {
bool MadeChange = false;
MemoryLocation Loc = MemoryLocation(F->getOperand(0));
SmallVector<BasicBlock *, 16> Blocks;
Blocks.push_back(F->getParent());
const DataLayout &DL = F->getModule()->getDataLayout();
while (!Blocks.empty()) {
BasicBlock *BB = Blocks.pop_back_val();
Instruction *InstPt = BB->getTerminator();
if (BB == F->getParent()) InstPt = F;
MemDepResult Dep =
MD->getPointerDependencyFrom(Loc, false, InstPt->getIterator(), BB);
while (Dep.isDef() || Dep.isClobber()) {
Instruction *Dependency = Dep.getInst();
if (!hasMemoryWrite(Dependency, *TLI) || !isRemovable(Dependency))
break;
Value *DepPointer =
GetUnderlyingObject(getStoredPointerOperand(Dependency), DL);
// Check for aliasing.
if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
break;
auto Next = ++Dependency->getIterator();
// DCE instructions only used to calculate that store
deleteDeadInstruction(Dependency, *MD, *TLI);
++NumFastStores;
MadeChange = true;
// Inst's old Dependency is now deleted. Compute the next dependency,
// which may also be dead, as in
// s[0] = 0;
// s[1] = 0; // This has just been deleted.
// free(s);
Dep = MD->getPointerDependencyFrom(Loc, false, Next, BB);
}
if (Dep.isNonLocal())
findUnconditionalPreds(Blocks, BB, DT);
}
return MadeChange;
}
/// Check to see if the specified location may alias any of the stack objects in
/// the DeadStackObjects set. If so, they become live because the location is
/// being loaded.
static void removeAccessedObjects(const MemoryLocation &LoadedLoc,
SmallSetVector<Value *, 16> &DeadStackObjects,
const DataLayout &DL, AliasAnalysis *AA,
const TargetLibraryInfo *TLI) {
const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr, DL);
// A constant can't be in the dead pointer set.
if (isa<Constant>(UnderlyingPointer))
return;
// If the kill pointer can be easily reduced to an alloca, don't bother doing
// extraneous AA queries.
if (isa<AllocaInst>(UnderlyingPointer) || isa<Argument>(UnderlyingPointer)) {
DeadStackObjects.remove(const_cast<Value*>(UnderlyingPointer));
return;
}
// Remove objects that could alias LoadedLoc.
DeadStackObjects.remove_if([&](Value *I) {
// See if the loaded location could alias the stack location.
MemoryLocation StackLoc(I, getPointerSize(I, DL, *TLI));
return !AA->isNoAlias(StackLoc, LoadedLoc);
});
}
/// Remove dead stores to stack-allocated locations in the function end block.
/// Ex:
/// %A = alloca i32
/// ...
/// store i32 1, i32* %A
/// ret void
static bool handleEndBlock(BasicBlock &BB, AliasAnalysis *AA,
MemoryDependenceResults *MD,
const TargetLibraryInfo *TLI) {
bool MadeChange = false;
// Keep track of all of the stack objects that are dead at the end of the
// function.
SmallSetVector<Value*, 16> DeadStackObjects;
// Find all of the alloca'd pointers in the entry block.
BasicBlock &Entry = BB.getParent()->front();
for (Instruction &I : Entry) {
if (isa<AllocaInst>(&I))
DeadStackObjects.insert(&I);
// Okay, so these are dead heap objects, but if the pointer never escapes
// then it's leaked by this function anyways.
else if (isAllocLikeFn(&I, TLI) && !PointerMayBeCaptured(&I, true, true))
DeadStackObjects.insert(&I);
}
// Treat byval or inalloca arguments the same, stores to them are dead at the
// end of the function.
for (Argument &AI : BB.getParent()->args())
if (AI.hasByValOrInAllocaAttr())
DeadStackObjects.insert(&AI);
const DataLayout &DL = BB.getModule()->getDataLayout();
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
// If we find a store, check to see if it points into a dead stack value.
if (hasMemoryWrite(&*BBI, *TLI) && isRemovable(&*BBI)) {
// See through pointer-to-pointer bitcasts
SmallVector<Value *, 4> Pointers;
GetUnderlyingObjects(getStoredPointerOperand(&*BBI), Pointers, DL);
// Stores to stack values are valid candidates for removal.
bool AllDead = true;
for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
E = Pointers.end(); I != E; ++I)
if (!DeadStackObjects.count(*I)) {
AllDead = false;
break;
}
if (AllDead) {
Instruction *Dead = &*BBI++;
DEBUG(dbgs() << "DSE: Dead Store at End of Block:\n DEAD: "
<< *Dead << "\n Objects: ";
for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
E = Pointers.end(); I != E; ++I) {
dbgs() << **I;
if (std::next(I) != E)
dbgs() << ", ";
}
dbgs() << '\n');
// DCE instructions only used to calculate that store.
deleteDeadInstruction(Dead, *MD, *TLI, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
continue;
}
}
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(&*BBI, TLI)) {
Instruction *Inst = &*BBI++;
deleteDeadInstruction(Inst, *MD, *TLI, &DeadStackObjects);
++NumFastOther;
MadeChange = true;
continue;
}
if (isa<AllocaInst>(BBI)) {
// Remove allocas from the list of dead stack objects; there can't be
// any references before the definition.
DeadStackObjects.remove(&*BBI);
continue;
}
if (auto CS = CallSite(&*BBI)) {
// Remove allocation function calls from the list of dead stack objects;
// there can't be any references before the definition.
if (isAllocLikeFn(&*BBI, TLI))
DeadStackObjects.remove(&*BBI);
// If this call does not access memory, it can't be loading any of our
// pointers.
if (AA->doesNotAccessMemory(CS))
continue;
// If the call might load from any of our allocas, then any store above
// the call is live.
DeadStackObjects.remove_if([&](Value *I) {
// See if the call site touches the value.
ModRefInfo A = AA->getModRefInfo(CS, I, getPointerSize(I, DL, *TLI));
return A == MRI_ModRef || A == MRI_Ref;
});
// If all of the allocas were clobbered by the call then we're not going
// to find anything else to process.
if (DeadStackObjects.empty())
break;
continue;
}
MemoryLocation LoadedLoc;
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
if (!L->isUnordered()) // Be conservative with atomic/volatile load
break;
LoadedLoc = MemoryLocation::get(L);
} else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
LoadedLoc = MemoryLocation::get(V);
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
LoadedLoc = MemoryLocation::getForSource(MTI);
} else if (!BBI->mayReadFromMemory()) {
// Instruction doesn't read memory. Note that stores that weren't removed
// above will hit this case.
continue;
} else {
// Unknown inst; assume it clobbers everything.
break;
}
// Remove any allocas from the DeadPointer set that are loaded, as this
// makes any stores above the access live.
removeAccessedObjects(LoadedLoc, DeadStackObjects, DL, AA, TLI);
// If all of the allocas were clobbered by the access then we're not going
// to find anything else to process.
if (DeadStackObjects.empty())
break;
}
return MadeChange;
}
static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
MemoryDependenceResults *MD, DominatorTree *DT,
const TargetLibraryInfo *TLI) {
const DataLayout &DL = BB.getModule()->getDataLayout();
bool MadeChange = false;
@ -517,7 +757,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// Handle 'free' calls specially.
if (CallInst *F = isFreeCall(Inst, TLI)) {
MadeChange |= HandleFree(F);
MadeChange |= handleFree(F, AA, MD, DT, TLI);
continue;
}
@ -530,11 +770,11 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
auto RemoveDeadInstAndUpdateBBI = [&](Instruction *DeadInst) {
// DeleteDeadInstruction can delete the current instruction. Save BBI
// deleteDeadInstruction can delete the current instruction. Save BBI
// in case we need it.
WeakVH NextInst(&*BBI);
DeleteDeadInstruction(DeadInst, *MD, *TLI);
deleteDeadInstruction(DeadInst, *MD, *TLI);
if (!NextInst) // Next instruction deleted.
BBI = BB.begin();
@ -547,7 +787,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
if (LoadInst *DepLoad = dyn_cast<LoadInst>(SI->getValueOperand())) {
if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
isRemovable(SI) &&
MemoryIsNotModifiedBetween(DepLoad, SI)) {
memoryIsNotModifiedBetween(DepLoad, SI, AA)) {
DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n "
<< "LOAD: " << *DepLoad << "\n STORE: " << *SI << '\n');
@ -566,7 +806,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
GetUnderlyingObject(SI->getPointerOperand(), DL));
if (UnderlyingPointer && isCallocLikeFn(UnderlyingPointer, TLI) &&
MemoryIsNotModifiedBetween(UnderlyingPointer, SI)) {
memoryIsNotModifiedBetween(UnderlyingPointer, SI, AA)) {
DEBUG(dbgs()
<< "DSE: Remove null store to the calloc'ed object:\n DEAD: "
<< *Inst << "\n OBJECT: " << *UnderlyingPointer << '\n');
@ -618,11 +858,11 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
<< *DepWrite << "\n KILLER: " << *Inst << '\n');
// Delete the store and now-dead instructions that feed it.
DeleteDeadInstruction(DepWrite, *MD, *TLI);
deleteDeadInstruction(DepWrite, *MD, *TLI);
++NumFastStores;
MadeChange = true;
// DeleteDeadInstruction can delete the current instruction in loop
// deleteDeadInstruction can delete the current instruction in loop
// cases, reset BBI.
BBI = Inst->getIterator();
if (BBI != BB.begin())
@ -698,309 +938,87 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// If this block ends in a return, unwind, or unreachable, all allocas are
// dead at its end, which means stores to them are also dead.
if (BB.getTerminator()->getNumSuccessors() == 0)
MadeChange |= handleEndBlock(BB);
MadeChange |= handleEndBlock(BB, AA, MD, TLI);
return MadeChange;
}
/// Returns true if the memory which is accessed by the second instruction is not
/// modified between the first and the second instruction.
/// Precondition: Second instruction must be dominated by the first
/// instruction.
bool DSE::MemoryIsNotModifiedBetween(Instruction *FirstI,
Instruction *SecondI) {
SmallVector<BasicBlock *, 16> WorkList;
SmallPtrSet<BasicBlock *, 8> Visited;
BasicBlock::iterator FirstBBI(FirstI);
++FirstBBI;
BasicBlock::iterator SecondBBI(SecondI);
BasicBlock *FirstBB = FirstI->getParent();
BasicBlock *SecondBB = SecondI->getParent();
MemoryLocation MemLoc = MemoryLocation::get(SecondI);
// Start checking the store-block.
WorkList.push_back(SecondBB);
bool isFirstBlock = true;
// Check all blocks going backward until we reach the load-block.
while (!WorkList.empty()) {
BasicBlock *B = WorkList.pop_back_val();
// Ignore instructions before LI if this is the FirstBB.
BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
BasicBlock::iterator EI;
if (isFirstBlock) {
// Ignore instructions after SI if this is the first visit of SecondBB.
assert(B == SecondBB && "first block is not the store block");
EI = SecondBBI;
isFirstBlock = false;
} else {
// It's not SecondBB or (in case of a loop) the second visit of SecondBB.
// In this case we also have to look at instructions after SI.
EI = B->end();
}
for (; BI != EI; ++BI) {
Instruction *I = &*BI;
if (I->mayWriteToMemory() && I != SecondI) {
auto Res = AA->getModRefInfo(I, MemLoc);
if (Res != MRI_NoModRef)
return false;
}
}
if (B != FirstBB) {
assert(B != &FirstBB->getParent()->getEntryBlock() &&
"Should not hit the entry block because SI must be dominated by LI");
for (auto PredI = pred_begin(B), PE = pred_end(B); PredI != PE; ++PredI) {
if (!Visited.insert(*PredI).second)
continue;
WorkList.push_back(*PredI);
}
}
}
return true;
}
/// Find all blocks that will unconditionally lead to the block BB and append
/// them to F.
static void FindUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
BasicBlock *BB, DominatorTree *DT) {
for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
BasicBlock *Pred = *I;
if (Pred == BB) continue;
TerminatorInst *PredTI = Pred->getTerminator();
if (PredTI->getNumSuccessors() != 1)
continue;
if (DT->isReachableFromEntry(Pred))
Blocks.push_back(Pred);
}
}
/// HandleFree - Handle frees of entire structures whose dependency is a store
/// to a field of that structure.
bool DSE::HandleFree(CallInst *F) {
static bool eliminateDeadStores(Function &F, AliasAnalysis *AA,
MemoryDependenceResults *MD, DominatorTree *DT,
const TargetLibraryInfo *TLI) {
bool MadeChange = false;
MemoryLocation Loc = MemoryLocation(F->getOperand(0));
SmallVector<BasicBlock *, 16> Blocks;
Blocks.push_back(F->getParent());
const DataLayout &DL = F->getModule()->getDataLayout();
while (!Blocks.empty()) {
BasicBlock *BB = Blocks.pop_back_val();
Instruction *InstPt = BB->getTerminator();
if (BB == F->getParent()) InstPt = F;
MemDepResult Dep =
MD->getPointerDependencyFrom(Loc, false, InstPt->getIterator(), BB);
while (Dep.isDef() || Dep.isClobber()) {
Instruction *Dependency = Dep.getInst();
if (!hasMemoryWrite(Dependency, *TLI) || !isRemovable(Dependency))
break;
Value *DepPointer =
GetUnderlyingObject(getStoredPointerOperand(Dependency), DL);
// Check for aliasing.
if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
break;
auto Next = ++Dependency->getIterator();
// DCE instructions only used to calculate that store
DeleteDeadInstruction(Dependency, *MD, *TLI);
++NumFastStores;
MadeChange = true;
// Inst's old Dependency is now deleted. Compute the next dependency,
// which may also be dead, as in
// s[0] = 0;
// s[1] = 0; // This has just been deleted.
// free(s);
Dep = MD->getPointerDependencyFrom(Loc, false, Next, BB);
}
if (Dep.isNonLocal())
FindUnconditionalPreds(Blocks, BB, DT);
}
for (BasicBlock &BB : F)
// Only check non-dead blocks. Dead blocks may have strange pointer
// cycles that will confuse alias analysis.
if (DT->isReachableFromEntry(&BB))
MadeChange |= eliminateDeadStores(BB, AA, MD, DT, TLI);
return MadeChange;
}
/// handleEndBlock - Remove dead stores to stack-allocated locations in the
/// function end block. Ex:
/// %A = alloca i32
/// ...
/// store i32 1, i32* %A
/// ret void
bool DSE::handleEndBlock(BasicBlock &BB) {
bool MadeChange = false;
//===----------------------------------------------------------------------===//
// DSE Pass
//===----------------------------------------------------------------------===//
PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) {
AliasAnalysis *AA = &AM.getResult<AAManager>(F);
DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
MemoryDependenceResults *MD = &AM.getResult<MemoryDependenceAnalysis>(F);
const TargetLibraryInfo *TLI = &AM.getResult<TargetLibraryAnalysis>(F);
// Keep track of all of the stack objects that are dead at the end of the
// function.
SmallSetVector<Value*, 16> DeadStackObjects;
// Find all of the alloca'd pointers in the entry block.
BasicBlock &Entry = BB.getParent()->front();
for (Instruction &I : Entry) {
if (isa<AllocaInst>(&I))
DeadStackObjects.insert(&I);
// Okay, so these are dead heap objects, but if the pointer never escapes
// then it's leaked by this function anyways.
else if (isAllocLikeFn(&I, TLI) && !PointerMayBeCaptured(&I, true, true))
DeadStackObjects.insert(&I);
}
// Treat byval or inalloca arguments the same, stores to them are dead at the
// end of the function.
for (Argument &AI : BB.getParent()->args())
if (AI.hasByValOrInAllocaAttr())
DeadStackObjects.insert(&AI);
const DataLayout &DL = BB.getModule()->getDataLayout();
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
// If we find a store, check to see if it points into a dead stack value.
if (hasMemoryWrite(&*BBI, *TLI) && isRemovable(&*BBI)) {
// See through pointer-to-pointer bitcasts
SmallVector<Value *, 4> Pointers;
GetUnderlyingObjects(getStoredPointerOperand(&*BBI), Pointers, DL);
// Stores to stack values are valid candidates for removal.
bool AllDead = true;
for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
E = Pointers.end(); I != E; ++I)
if (!DeadStackObjects.count(*I)) {
AllDead = false;
break;
}
if (AllDead) {
Instruction *Dead = &*BBI++;
DEBUG(dbgs() << "DSE: Dead Store at End of Block:\n DEAD: "
<< *Dead << "\n Objects: ";
for (SmallVectorImpl<Value *>::iterator I = Pointers.begin(),
E = Pointers.end(); I != E; ++I) {
dbgs() << **I;
if (std::next(I) != E)
dbgs() << ", ";
}
dbgs() << '\n');
// DCE instructions only used to calculate that store.
DeleteDeadInstruction(Dead, *MD, *TLI, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
continue;
}
}
// Remove any dead non-memory-mutating instructions.
if (isInstructionTriviallyDead(&*BBI, TLI)) {
Instruction *Inst = &*BBI++;
DeleteDeadInstruction(Inst, *MD, *TLI, &DeadStackObjects);
++NumFastOther;
MadeChange = true;
continue;
}
if (isa<AllocaInst>(BBI)) {
// Remove allocas from the list of dead stack objects; there can't be
// any references before the definition.
DeadStackObjects.remove(&*BBI);
continue;
}
if (auto CS = CallSite(&*BBI)) {
// Remove allocation function calls from the list of dead stack objects;
// there can't be any references before the definition.
if (isAllocLikeFn(&*BBI, TLI))
DeadStackObjects.remove(&*BBI);
// If this call does not access memory, it can't be loading any of our
// pointers.
if (AA->doesNotAccessMemory(CS))
continue;
// If the call might load from any of our allocas, then any store above
// the call is live.
DeadStackObjects.remove_if([&](Value *I) {
// See if the call site touches the value.
ModRefInfo A = AA->getModRefInfo(CS, I, getPointerSize(I, DL, *TLI));
return A == MRI_ModRef || A == MRI_Ref;
});
// If all of the allocas were clobbered by the call then we're not going
// to find anything else to process.
if (DeadStackObjects.empty())
break;
continue;
}
MemoryLocation LoadedLoc;
// If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
if (!L->isUnordered()) // Be conservative with atomic/volatile load
break;
LoadedLoc = MemoryLocation::get(L);
} else if (VAArgInst *V = dyn_cast<VAArgInst>(BBI)) {
LoadedLoc = MemoryLocation::get(V);
} else if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(BBI)) {
LoadedLoc = MemoryLocation::getForSource(MTI);
} else if (!BBI->mayReadFromMemory()) {
// Instruction doesn't read memory. Note that stores that weren't removed
// above will hit this case.
continue;
} else {
// Unknown inst; assume it clobbers everything.
break;
}
// Remove any allocas from the DeadPointer set that are loaded, as this
// makes any stores above the access live.
RemoveAccessedObjects(LoadedLoc, DeadStackObjects, DL);
// If all of the allocas were clobbered by the access then we're not going
// to find anything else to process.
if (DeadStackObjects.empty())
break;
}
return MadeChange;
if (!eliminateDeadStores(F, AA, MD, DT, TLI))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
PA.preserve<GlobalsAA>();
PA.preserve<MemoryDependenceAnalysis>();
return PA;
}
/// RemoveAccessedObjects - Check to see if the specified location may alias any
/// of the stack objects in the DeadStackObjects set. If so, they become live
/// because the location is being loaded.
void DSE::RemoveAccessedObjects(const MemoryLocation &LoadedLoc,
SmallSetVector<Value *, 16> &DeadStackObjects,
const DataLayout &DL) {
const Value *UnderlyingPointer = GetUnderlyingObject(LoadedLoc.Ptr, DL);
// A constant can't be in the dead pointer set.
if (isa<Constant>(UnderlyingPointer))
return;
// If the kill pointer can be easily reduced to an alloca, don't bother doing
// extraneous AA queries.
if (isa<AllocaInst>(UnderlyingPointer) || isa<Argument>(UnderlyingPointer)) {
DeadStackObjects.remove(const_cast<Value*>(UnderlyingPointer));
return;
/// A legacy pass for the legacy pass manager that wraps \c DSEPass.
class DSELegacyPass : public FunctionPass {
public:
DSELegacyPass() : FunctionPass(ID) {
initializeDSELegacyPassPass(*PassRegistry::getPassRegistry());
}
// Remove objects that could alias LoadedLoc.
DeadStackObjects.remove_if([&](Value *I) {
// See if the loaded location could alias the stack location.
MemoryLocation StackLoc(I, getPointerSize(I, DL, *TLI));
return !AA->isNoAlias(StackLoc, LoadedLoc);
});
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
MemoryDependenceResults *MD =
&getAnalysis<MemoryDependenceWrapperPass>().getMemDep();
const TargetLibraryInfo *TLI =
&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
return eliminateDeadStores(F, AA, MD, DT, TLI);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
AU.addRequired<MemoryDependenceWrapperPass>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
AU.addPreserved<MemoryDependenceWrapperPass>();
}
static char ID; // Pass identification, replacement for typeid
};
char DSELegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(DSELegacyPass, "dse", "Dead Store Elimination", false,
false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(DSELegacyPass, "dse", "Dead Store Elimination", false,
false)
FunctionPass *llvm::createDeadStoreEliminationPass() {
return new DSELegacyPass();
}

2
llvm/lib/Transforms/Scalar/Scalar.cpp
View File

@ -40,7 +40,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
initializeDCELegacyPassPass(Registry);
initializeDeadInstEliminationPass(Registry);
initializeScalarizerPass(Registry);
initializeDSEPass(Registry);
initializeDSELegacyPassPass(Registry);
initializeGVNLegacyPassPass(Registry);
initializeEarlyCSELegacyPassPass(Registry);
initializeFlattenCFGPassPass(Registry);

1
llvm/test/Transforms/DeadStoreElimination/simple.ll
View File

@ -1,4 +1,5 @@
; RUN: opt < %s -basicaa -dse -S | FileCheck %s
; RUN: opt < %s -aa-pipeline=basic-aa -passes=dse -S | FileCheck %s
target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind