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rewrite a big chunk of how DSE does recursive dead operand

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elimination to use more modern infrastructure.  Also do a bunch
of small cleanups.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60201 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-11-28 00:27:14 +00:00
parent bfdef3a6b2
commit 925451e020
1 changed files with 104 additions and 180 deletions
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284
lib/Transforms/Scalar/DeadStoreElimination.cpp
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@ -22,7 +22,6 @@
#include "llvm/Instructions.h" #include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h" #include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h" #include "llvm/Pass.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h" #include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AliasAnalysis.h"
@ -49,17 +48,14 @@ namespace {
} }
bool runOnBasicBlock(BasicBlock &BB); bool runOnBasicBlock(BasicBlock &BB);
bool handleFreeWithNonTrivialDependency(FreeInst* F, bool handleFreeWithNonTrivialDependency(FreeInst *F, Instruction *Dep);
Instruction* dependency, bool handleEndBlock(BasicBlock &BB);
SetVector<Instruction*>& possiblyDead);
bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
bool RemoveUndeadPointers(Value* pointer, uint64_t killPointerSize, bool RemoveUndeadPointers(Value* pointer, uint64_t killPointerSize,
BasicBlock::iterator& BBI, BasicBlock::iterator& BBI,
SmallPtrSet<Value*, 64>& deadPointers, SmallPtrSet<Value*, 64>& deadPointers);
SetVector<Instruction*>& possiblyDead); void DeleteDeadInstruction(Instruction *I,
void DeleteDeadInstructionChains(Instruction *I, SmallPtrSet<Value*, 64> *deadPointers = 0);
SetVector<Instruction*> &DeadInsts);
// getAnalysisUsage - We require post dominance frontiers (aka Control // getAnalysisUsage - We require post dominance frontiers (aka Control
// Dependence Graph) // Dependence Graph)
@ -87,8 +83,6 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// Record the last-seen store to this pointer // Record the last-seen store to this pointer
DenseMap<Value*, StoreInst*> lastStore; DenseMap<Value*, StoreInst*> lastStore;
// Record instructions possibly made dead by deleting a store
SetVector<Instruction*> possiblyDead;
bool MadeChange = false; bool MadeChange = false;
@ -127,20 +121,11 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
continue; continue;
} }
// Remove it! // Delete the store and now-dead instructions that feed it.
MD.removeInstruction(last); DeleteDeadInstruction(last);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(last->getOperand(1)))
possiblyDead.insert(D);
last->eraseFromParent();
NumFastStores++; NumFastStores++;
deletedStore = true; deletedStore = true;
MadeChange = true; MadeChange = true;
break; break;
} }
} }
@ -148,9 +133,8 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// Handle frees whose dependencies are non-trivial. // Handle frees whose dependencies are non-trivial.
if (FreeInst* F = dyn_cast<FreeInst>(BBI)) { if (FreeInst* F = dyn_cast<FreeInst>(BBI)) {
if (!deletedStore) if (!deletedStore)
MadeChange |= handleFreeWithNonTrivialDependency(F, MadeChange |= handleFreeWithNonTrivialDependency(F,MD.getDependency(F));
MD.getDependency(F),
possiblyDead);
// No known stores after the free // No known stores after the free
last = 0; last = 0;
} else { } else {
@ -164,19 +148,13 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
if (!S->isVolatile() && S->getParent() == L->getParent() && if (!S->isVolatile() && S->getParent() == L->getParent() &&
S->getPointerOperand() == L->getPointerOperand() && S->getPointerOperand() == L->getPointerOperand() &&
( dep == MemoryDependenceAnalysis::None || (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal || dep == MemoryDependenceAnalysis::NonLocal ||
DT.dominates(dep, L))) { DT.dominates(dep, L))) {
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
possiblyDead.insert(D);
// Avoid iterator invalidation. // Avoid iterator invalidation.
BBI--; BBI++;
DeleteDeadInstruction(S);
MD.removeInstruction(S);
S->eraseFromParent();
NumFastStores++; NumFastStores++;
MadeChange = true; MadeChange = true;
} else } else
@ -191,25 +169,16 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// If this block ends in a return, unwind, unreachable, and eventually // If this block ends in a return, unwind, unreachable, and eventually
// tailcall, then all allocas are dead at its end. // tailcall, then all allocas are dead at its end.
if (BB.getTerminator()->getNumSuccessors() == 0) if (BB.getTerminator()->getNumSuccessors() == 0)
MadeChange |= handleEndBlock(BB, possiblyDead); MadeChange |= handleEndBlock(BB);
// Do a trivial DCE
while (!possiblyDead.empty()) {
Instruction *I = possiblyDead.back();
possiblyDead.pop_back();
DeleteDeadInstructionChains(I, possiblyDead);
}
return MadeChange; return MadeChange;
} }
/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose /// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
/// dependency is a store to a field of that structure /// dependency is a store to a field of that structure.
bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep, bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep) {
SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>(); TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
if (dep == MemoryDependenceAnalysis::None || if (dep == MemoryDependenceAnalysis::None ||
dep == MemoryDependenceAnalysis::NonLocal) dep == MemoryDependenceAnalysis::NonLocal)
@ -229,22 +198,13 @@ bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0U, AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0U,
depPointer, depPointerSize); depPointer, depPointerSize);
if (A == AliasAnalysis::MustAlias) { if (A != AliasAnalysis::MustAlias)
// Remove it! return false;
MD.removeInstruction(dependency);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(1)))
possiblyDead.insert(D);
dependency->eraseFromParent();
NumFastStores++;
return true;
}
return false; // DCE instructions only used to calculate that store
DeleteDeadInstruction(dependency);
NumFastStores++;
return true;
} }
/// handleEndBlock - Remove dead stores to stack-allocated locations in the /// handleEndBlock - Remove dead stores to stack-allocated locations in the
@ -253,22 +213,23 @@ bool DSE::handleFreeWithNonTrivialDependency(FreeInst* F, Instruction* dep,
/// ... /// ...
/// store i32 1, i32* %A /// store i32 1, i32* %A
/// ret void /// ret void
bool DSE::handleEndBlock(BasicBlock& BB, bool DSE::handleEndBlock(BasicBlock &BB) {
SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>(); TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
bool MadeChange = false; bool MadeChange = false;
// Pointers alloca'd in this function are dead in the end block // Pointers alloca'd in this function are dead in the end block
SmallPtrSet<Value*, 64> deadPointers; SmallPtrSet<Value*, 64> deadPointers;
// Find all of the alloca'd pointers in the entry block // Find all of the alloca'd pointers in the entry block.
BasicBlock *Entry = BB.getParent()->begin(); BasicBlock *Entry = BB.getParent()->begin();
for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I) for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
deadPointers.insert(AI); deadPointers.insert(AI);
// Treat byval arguments the same, stores to them are dead at the end of the
// function.
for (Function::arg_iterator AI = BB.getParent()->arg_begin(), for (Function::arg_iterator AI = BB.getParent()->arg_begin(),
AE = BB.getParent()->arg_end(); AI != AE; ++AI) AE = BB.getParent()->arg_end(); AI != AE; ++AI)
if (AI->hasByValAttr()) if (AI->hasByValAttr())
@ -278,7 +239,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){ for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI; --BBI;
// If we find a store whose pointer is dead... // If we find a store whose pointer is dead.
if (StoreInst* S = dyn_cast<StoreInst>(BBI)) { if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
if (!S->isVolatile()) { if (!S->isVolatile()) {
// See through pointer-to-pointer bitcasts // See through pointer-to-pointer bitcasts
@ -287,71 +248,45 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// Alloca'd pointers or byval arguments (which are functionally like // Alloca'd pointers or byval arguments (which are functionally like
// alloca's) are valid candidates for removal. // alloca's) are valid candidates for removal.
if (deadPointers.count(pointerOperand)) { if (deadPointers.count(pointerOperand)) {
// Remove it! // DCE instructions only used to calculate that store.
MD.removeInstruction(S);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
possiblyDead.insert(D);
BBI++; BBI++;
MD.removeInstruction(S); DeleteDeadInstruction(S, &deadPointers);
S->eraseFromParent();
NumFastStores++; NumFastStores++;
MadeChange = true; MadeChange = true;
} }
} }
continue; continue;
}
// We can also remove memcpy's to local variables at the end of a function // We can also remove memcpy's to local variables at the end of a function.
} else if (MemCpyInst* M = dyn_cast<MemCpyInst>(BBI)) { if (MemCpyInst *M = dyn_cast<MemCpyInst>(BBI)) {
Value* dest = M->getDest()->getUnderlyingObject(); Value *dest = M->getDest()->getUnderlyingObject();
if (deadPointers.count(dest)) { if (deadPointers.count(dest)) {
MD.removeInstruction(M);
// DCE instructions only used to calculate that memcpy
if (Instruction* D = dyn_cast<Instruction>(M->getRawSource()))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(M->getLength()))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(M->getRawDest()))
possiblyDead.insert(D);
BBI++; BBI++;
M->eraseFromParent(); DeleteDeadInstruction(M, &deadPointers);
NumFastOther++; NumFastOther++;
MadeChange = true; MadeChange = true;
continue; continue;
} }
// Because a memcpy is also a load, we can't skip it if we didn't remove it // Because a memcpy is also a load, we can't skip it if we didn't remove
// it.
} }
Value* killPointer = 0; Value* killPointer = 0;
uint64_t killPointerSize = ~0UL; uint64_t killPointerSize = ~0UL;
// If we encounter a use of the pointer, it is no longer considered dead // If we encounter a use of the pointer, it is no longer considered dead
if (LoadInst* L = dyn_cast<LoadInst>(BBI)) { if (LoadInst *L = dyn_cast<LoadInst>(BBI)) {
// However, if this load is unused and not volatile, we can go ahead and // However, if this load is unused and not volatile, we can go ahead and
// remove it, and not have to worry about it making our pointer undead! // remove it, and not have to worry about it making our pointer undead!
if (L->use_empty() && !L->isVolatile()) { if (L->use_empty() && !L->isVolatile()) {
MD.removeInstruction(L);
// DCE instructions only used to calculate that load
if (Instruction* D = dyn_cast<Instruction>(L->getPointerOperand()))
possiblyDead.insert(D);
BBI++; BBI++;
L->eraseFromParent(); DeleteDeadInstruction(L, &deadPointers);
NumFastOther++; NumFastOther++;
MadeChange = true; MadeChange = true;
possiblyDead.remove(L);
continue; continue;
} }
@ -368,17 +303,10 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// Dead alloca's can be DCE'd when we reach them // Dead alloca's can be DCE'd when we reach them
if (A->use_empty()) { if (A->use_empty()) {
MD.removeInstruction(A);
// DCE instructions only used to calculate that load
if (Instruction* D = dyn_cast<Instruction>(A->getArraySize()))
possiblyDead.insert(D);
BBI++; BBI++;
A->eraseFromParent(); DeleteDeadInstruction(A, &deadPointers);
NumFastOther++; NumFastOther++;
MadeChange = true; MadeChange = true;
possiblyDead.remove(A);
} }
continue; continue;
@ -434,25 +362,14 @@ bool DSE::handleEndBlock(BasicBlock& BB,
deadPointers.erase(*I); deadPointers.erase(*I);
continue; continue;
} else { } else if (isInstructionTriviallyDead(BBI)) {
// For any non-memory-affecting non-terminators, DCE them as we reach them // For any non-memory-affecting non-terminators, DCE them as we reach them
Instruction *CI = BBI; Instruction *Inst = BBI;
if (!CI->isTerminator() && CI->use_empty() && !isa<FreeInst>(CI)) { BBI++;
DeleteDeadInstruction(Inst, &deadPointers);
// DCE instructions only used to calculate that load NumFastOther++;
for (Instruction::op_iterator OI = CI->op_begin(), OE = CI->op_end(); MadeChange = true;
OI != OE; ++OI) continue;
if (Instruction* D = dyn_cast<Instruction>(OI))
possiblyDead.insert(D);
BBI++;
CI->eraseFromParent();
NumFastOther++;
MadeChange = true;
possiblyDead.remove(CI);
continue;
}
} }
if (!killPointer) if (!killPointer)
@ -462,7 +379,7 @@ bool DSE::handleEndBlock(BasicBlock& BB,
// Deal with undead pointers // Deal with undead pointers
MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI, MadeChange |= RemoveUndeadPointers(killPointer, killPointerSize, BBI,
deadPointers, possiblyDead); deadPointers);
} }
return MadeChange; return MadeChange;
@ -471,38 +388,36 @@ bool DSE::handleEndBlock(BasicBlock& BB,
/// RemoveUndeadPointers - check for uses of a pointer that make it /// RemoveUndeadPointers - check for uses of a pointer that make it
/// undead when scanning for dead stores to alloca's. /// undead when scanning for dead stores to alloca's.
bool DSE::RemoveUndeadPointers(Value* killPointer, uint64_t killPointerSize, bool DSE::RemoveUndeadPointers(Value* killPointer, uint64_t killPointerSize,
BasicBlock::iterator& BBI, BasicBlock::iterator &BBI,
SmallPtrSet<Value*, 64>& deadPointers, SmallPtrSet<Value*, 64>& deadPointers) {
SetVector<Instruction*>& possiblyDead) {
TargetData &TD = getAnalysis<TargetData>(); TargetData &TD = getAnalysis<TargetData>();
AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
// If the kill pointer can be easily reduced to an alloca, // If the kill pointer can be easily reduced to an alloca,
// don't bother doing extraneous AA queries // don't bother doing extraneous AA queries.
if (deadPointers.count(killPointer)) { if (deadPointers.count(killPointer)) {
deadPointers.erase(killPointer); deadPointers.erase(killPointer);
return false; return false;
} else if (isa<GlobalValue>(killPointer)) {
// A global can't be in the dead pointer set
return false;
} }
// A global can't be in the dead pointer set.
if (isa<GlobalValue>(killPointer))
return false;
bool MadeChange = false; bool MadeChange = false;
std::vector<Value*> undead; SmallVector<Value*, 16> undead;
for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(), for (SmallPtrSet<Value*, 64>::iterator I = deadPointers.begin(),
E = deadPointers.end(); I != E; ++I) { E = deadPointers.end(); I != E; ++I) {
// Get size information for the alloca // Get size information for the alloca.
unsigned pointerSize = ~0U; unsigned pointerSize = ~0U;
if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) { if (AllocaInst* A = dyn_cast<AllocaInst>(*I)) {
if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize())) if (ConstantInt* C = dyn_cast<ConstantInt>(A->getArraySize()))
pointerSize = C->getZExtValue() * \ pointerSize = C->getZExtValue() *
TD.getABITypeSize(A->getAllocatedType()); TD.getABITypeSize(A->getAllocatedType());
} else { } else {
const PointerType* PT = cast<PointerType>( const PointerType* PT = cast<PointerType>(cast<Argument>(*I)->getType());
cast<Argument>(*I)->getType());
pointerSize = TD.getABITypeSize(PT->getElementType()); pointerSize = TD.getABITypeSize(PT->getElementType());
} }
@ -515,56 +430,65 @@ bool DSE::RemoveUndeadPointers(Value* killPointer, uint64_t killPointerSize,
StoreInst* S = cast<StoreInst>(BBI); StoreInst* S = cast<StoreInst>(BBI);
// Remove it! // Remove it!
MD.removeInstruction(S);
// DCE instructions only used to calculate that store
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
possiblyDead.insert(D);
if (Instruction* D = dyn_cast<Instruction>(S->getOperand(1)))
possiblyDead.insert(D);
BBI++; BBI++;
S->eraseFromParent(); DeleteDeadInstruction(S, &deadPointers);
NumFastStores++; NumFastStores++;
MadeChange = true; MadeChange = true;
continue; continue;
// Otherwise, it is undead // Otherwise, it is undead
} else if (A != AliasAnalysis::NoAlias) } else if (A != AliasAnalysis::NoAlias)
undead.push_back(*I); undead.push_back(*I);
} }
for (std::vector<Value*>::iterator I = undead.begin(), E = undead.end(); for (SmallVector<Value*, 16>::iterator I = undead.begin(), E = undead.end();
I != E; ++I) I != E; ++I)
deadPointers.erase(*I); deadPointers.erase(*I);
return MadeChange; return MadeChange;
} }
/// DeleteDeadInstructionChains - takes an instruction and a setvector of /// DeleteDeadInstruction - Delete this instruction. Before we do, go through
/// dead instructions. If I is dead, it is erased, and its operands are /// and zero out all the operands of this instruction. If any of them become
/// checked for deadness. If they are dead, they are added to the dead /// dead, delete them and the computation tree that feeds them.
/// setvector. ///
void DSE::DeleteDeadInstructionChains(Instruction *I, /// If ValueSet is non-null, remove any deleted instructions from it as well.
SetVector<Instruction*> &DeadInsts) { ///
// Instruction must be dead. void DSE::DeleteDeadInstruction(Instruction *I,
if (!I->use_empty() || !isInstructionTriviallyDead(I)) return; SmallPtrSet<Value*, 64> *ValueSet) {
SmallVector<Instruction*, 32> NowDeadInsts;
NowDeadInsts.push_back(I);
--NumFastOther;
// Let the memory dependence know // Before we touch this instruction, remove it from memdep!
getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I); MemoryDependenceAnalysis &MDA = getAnalysis<MemoryDependenceAnalysis>();
while (!NowDeadInsts.empty()) {
// See if this made any operands dead. We do it this way in case the Instruction *DeadInst = NowDeadInsts.back();
// instruction uses the same operand twice. We don't want to delete a NowDeadInsts.pop_back();
// value then reference it.
for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
if (I->getOperand(i)->hasOneUse())
if (Instruction* Op = dyn_cast<Instruction>(I->getOperand(i)))
DeadInsts.insert(Op); // Attempt to nuke it later.
I->setOperand(i, 0); // Drop from the operand list. ++NumFastOther;
// This instruction is dead, zap it, in stages. Start by removing it from
// MemDep, which needs to know the operands and needs it to be in the
// function.
MDA.removeInstruction(DeadInst);
for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
Value *Op = DeadInst->getOperand(op);
DeadInst->setOperand(op, 0);
// If this operand just became dead, add it to the NowDeadInsts list.
if (!Op->use_empty()) continue;
if (Instruction *OpI = dyn_cast<Instruction>(Op))
if (isInstructionTriviallyDead(OpI))
NowDeadInsts.push_back(OpI);
}
DeadInst->eraseFromParent();
if (ValueSet) ValueSet->erase(DeadInst);
} }
I->eraseFromParent();
++NumFastOther;
} }