llvm/lib/Transforms/Scalar/FastDSE.cpp - toolchain/llvm-project - Gitiles

 //===- DeadStoreElimination.cpp - Dead Store Elimination ------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file was developed by Owen Anderson and 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.
 //
 //===----------------------------------------------------------------------===//

 #define DEBUG_TYPE "fdse"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/Pass.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Support/Compiler.h"
 using namespace llvm;

 STATISTIC(NumFastStores, "Number of stores deleted");
 STATISTIC(NumFastOther , "Number of other instrs removed");

 namespace {
   struct VISIBILITY_HIDDEN FDSE : public FunctionPass {
     static char ID; // Pass identification, replacement for typeid
     FDSE() : FunctionPass((intptr_t)&ID) {}

     virtual bool runOnFunction(Function &F) {
       bool Changed = false;
       for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
         Changed |= runOnBasicBlock(*I);
       return Changed;
     }

     bool runOnBasicBlock(BasicBlock &BB);
     bool handleFreeWithNonTrivialDependency(FreeInst* F, StoreInst* dependency,
                                             SetVector<Instruction*>& possiblyDead);
     bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
     void DeleteDeadInstructionChains(Instruction *I,
                                      SetVector<Instruction*> &DeadInsts);

     // getAnalysisUsage - We require post dominance frontiers (aka Control
     // Dependence Graph)
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.setPreservesCFG();
       AU.addRequired<TargetData>();
       AU.addRequired<AliasAnalysis>();
       AU.addRequired<MemoryDependenceAnalysis>();
       AU.addPreserved<AliasAnalysis>();
       AU.addPreserved<MemoryDependenceAnalysis>();
     }
   };
   char FDSE::ID = 0;
   RegisterPass<FDSE> X("fdse", "Fast Dead Store Elimination");
 }

 FunctionPass *llvm::createFastDeadStoreEliminationPass() { return new FDSE(); }

 bool FDSE::runOnBasicBlock(BasicBlock &BB) {
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
   MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();

   // Record the last-seen store to this pointer
   DenseMap<Value*, StoreInst*> lastStore;
   // Record instructions possibly made dead by deleting a store
   SetVector<Instruction*> possiblyDead;

   bool MadeChange = false;

   // Do a top-down walk on the BB
   for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ++BBI) {
     // If we find a store or a free...
     if (isa<StoreInst>(BBI) || isa<FreeInst>(BBI)) {
       Value* pointer = 0;
       if (StoreInst* S = dyn_cast<StoreInst>(BBI))
         pointer = S->getPointerOperand();
       else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
         pointer = F->getPointerOperand();
       assert(pointer && "Not a free or a store?");

       StoreInst*& last = lastStore[pointer];

       // ... to a pointer that has been stored to before...
       if (last) {

         // ... and no other memory dependencies are between them....
         if (MD.getDependency(BBI) == last) {

           // Remove it!
           MD.removeInstruction(last);
           AA.deleteValue(last);

           // DCE instructions only used to calculate that store
           if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
             possiblyDead.insert(D);

           last->eraseFromParent();
           NumFastStores++;
           MadeChange = true;

         // If this is a free, check for a non-trivial dependency
         } else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
           MadeChange |= handleFreeWithNonTrivialDependency(F, last, possiblyDead);
       }

       // Update our most-recent-store map
       if (StoreInst* S = dyn_cast<StoreInst>(BBI))
         last = S;
       else
         last = 0;
     }
   }

   // If this block ends in a return, unwind, unreachable, and eventually
   // tailcall, then all allocas are dead at its end.
   if (BB.getTerminator()->getNumSuccessors() == 0)
     MadeChange |= handleEndBlock(BB, possiblyDead);

   // Do a trivial DCE
   while (!possiblyDead.empty()) {
     Instruction *I = possiblyDead.back();
     possiblyDead.pop_back();
     DeleteDeadInstructionChains(I, possiblyDead);
   }

   return MadeChange;
 }

 /// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
 /// dependency is a store to a field of that structure
 bool FDSE::handleFreeWithNonTrivialDependency(FreeInst* F, StoreInst* dependency,
                                               SetVector<Instruction*>& possiblyDead) {
   TargetData &TD = getAnalysis<TargetData>();
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
   MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();

   Value* depPointer = dependency->getPointerOperand();
   unsigned depPointerSize = TD.getTypeSize(dependency->getOperand(0)->getType());

   // Check for aliasing
   AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
                                           depPointer, depPointerSize);

   if (A == AliasAnalysis::MustAlias) {
     // Remove it!
     MD.removeInstruction(dependency);
     AA.deleteValue(dependency);

     // DCE instructions only used to calculate that store
     if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
       possiblyDead.insert(D);

     dependency->eraseFromParent();
     NumFastStores++;
     return true;
   }

   return false;
 }

 /// handleEndBlock - Remove dead stores to stack-allocated locations in the function
 /// end block
 bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead) {
   AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
   MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();

   bool MadeChange = false;

   // Pointers alloca'd in this function are dead in the end block
   SmallPtrSet<AllocaInst*, 4> deadPointers;

   // Find all of the alloca'd pointers in the entry block
   BasicBlock *Entry = BB.getParent()->begin();
   for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
     if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
       deadPointers.insert(AI);

   // Scan the basic block backwards
   for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
     --BBI;

     if (deadPointers.empty())
       break;

     // If we find a store whose pointer is dead...
     if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
       if (deadPointers.count(S->getPointerOperand())){
         // Remove it!
         MD.removeInstruction(S);
         AA.deleteValue(S);

         // DCE instructions only used to calculate that store
         if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
           possiblyDead.insert(D);

         BBI++;
         S->eraseFromParent();
         NumFastStores++;
         MadeChange = true;
       }

     // If we encounter a use of the pointer, it is no longer considered dead
     } else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
       deadPointers.erase(L->getPointerOperand());
     } else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
       deadPointers.erase(V->getOperand(0));
     }
   }

   return MadeChange;
 }

 void FDSE::DeleteDeadInstructionChains(Instruction *I,
                                       SetVector<Instruction*> &DeadInsts) {
   // Instruction must be dead.
   if (!I->use_empty() || !isInstructionTriviallyDead(I)) return;

   // Let the memory dependence know
   getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I);
   getAnalysis<AliasAnalysis>().deleteValue(I);

   // See if this made any operands dead.  We do it this way in case the
   // instruction uses the same operand twice.  We don't want to delete a
   // 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.
   }

   I->eraseFromParent();
   ++NumFastOther;
 }
	//===- DeadStoreElimination.cpp - Dead Store Elimination ------------------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file was developed by Owen Anderson and 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.
	//
	//===----------------------------------------------------------------------===//

	#define DEBUG_TYPE "fdse"
	#include "llvm/Transforms/Scalar.h"
	#include "llvm/Function.h"
	#include "llvm/Instructions.h"
	#include "llvm/Pass.h"
	#include "llvm/ADT/SetVector.h"
	#include "llvm/ADT/SmallPtrSet.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/Analysis/AliasAnalysis.h"
	#include "llvm/Analysis/MemoryDependenceAnalysis.h"
	#include "llvm/Target/TargetData.h"
	#include "llvm/Transforms/Utils/Local.h"
	#include "llvm/Support/Compiler.h"
	using namespace llvm;

	STATISTIC(NumFastStores, "Number of stores deleted");
	STATISTIC(NumFastOther , "Number of other instrs removed");

	namespace {
	struct VISIBILITY_HIDDEN FDSE : public FunctionPass {
	static char ID; // Pass identification, replacement for typeid
	FDSE() : FunctionPass((intptr_t)&ID) {}

	virtual bool runOnFunction(Function &F) {
	bool Changed = false;
	for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
	Changed \|= runOnBasicBlock(*I);
	return Changed;
	}

	bool runOnBasicBlock(BasicBlock &BB);
	bool handleFreeWithNonTrivialDependency(FreeInst* F, StoreInst* dependency,
	SetVector<Instruction*>& possiblyDead);
	bool handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead);
	void DeleteDeadInstructionChains(Instruction *I,
	SetVector<Instruction*> &DeadInsts);

	// getAnalysisUsage - We require post dominance frontiers (aka Control
	// Dependence Graph)
	virtual void getAnalysisUsage(AnalysisUsage &AU) const {
	AU.setPreservesCFG();
	AU.addRequired<TargetData>();
	AU.addRequired<AliasAnalysis>();
	AU.addRequired<MemoryDependenceAnalysis>();
	AU.addPreserved<AliasAnalysis>();
	AU.addPreserved<MemoryDependenceAnalysis>();
	}
	};
	char FDSE::ID = 0;
	RegisterPass<FDSE> X("fdse", "Fast Dead Store Elimination");
	}

	FunctionPass *llvm::createFastDeadStoreEliminationPass() { return new FDSE(); }

	bool FDSE::runOnBasicBlock(BasicBlock &BB) {
	AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
	MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();

	// Record the last-seen store to this pointer
	DenseMap<Value, StoreInst> lastStore;
	// Record instructions possibly made dead by deleting a store
	SetVector<Instruction*> possiblyDead;

	bool MadeChange = false;

	// Do a top-down walk on the BB
	for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ++BBI) {
	// If we find a store or a free...
	if (isa<StoreInst>(BBI) \|\| isa<FreeInst>(BBI)) {
	Value* pointer = 0;
	if (StoreInst* S = dyn_cast<StoreInst>(BBI))
	pointer = S->getPointerOperand();
	else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
	pointer = F->getPointerOperand();
	assert(pointer && "Not a free or a store?");

	StoreInst*& last = lastStore[pointer];

	// ... to a pointer that has been stored to before...
	if (last) {

	// ... and no other memory dependencies are between them....
	if (MD.getDependency(BBI) == last) {

	// Remove it!
	MD.removeInstruction(last);
	AA.deleteValue(last);

	// DCE instructions only used to calculate that store
	if (Instruction* D = dyn_cast<Instruction>(last->getOperand(0)))
	possiblyDead.insert(D);

	last->eraseFromParent();
	NumFastStores++;
	MadeChange = true;

	// If this is a free, check for a non-trivial dependency
	} else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
	MadeChange \|= handleFreeWithNonTrivialDependency(F, last, possiblyDead);
	}

	// Update our most-recent-store map
	if (StoreInst* S = dyn_cast<StoreInst>(BBI))
	last = S;
	else
	last = 0;
	}
	}

	// If this block ends in a return, unwind, unreachable, and eventually
	// tailcall, then all allocas are dead at its end.
	if (BB.getTerminator()->getNumSuccessors() == 0)
	MadeChange \|= handleEndBlock(BB, possiblyDead);

	// Do a trivial DCE
	while (!possiblyDead.empty()) {
	Instruction *I = possiblyDead.back();
	possiblyDead.pop_back();
	DeleteDeadInstructionChains(I, possiblyDead);
	}

	return MadeChange;
	}

	/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
	/// dependency is a store to a field of that structure
	bool FDSE::handleFreeWithNonTrivialDependency(FreeInst* F, StoreInst* dependency,
	SetVector<Instruction*>& possiblyDead) {
	TargetData &TD = getAnalysis<TargetData>();
	AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
	MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();

	Value* depPointer = dependency->getPointerOperand();
	unsigned depPointerSize = TD.getTypeSize(dependency->getOperand(0)->getType());

	// Check for aliasing
	AliasAnalysis::AliasResult A = AA.alias(F->getPointerOperand(), ~0UL,
	depPointer, depPointerSize);

	if (A == AliasAnalysis::MustAlias) {
	// Remove it!
	MD.removeInstruction(dependency);
	AA.deleteValue(dependency);

	// DCE instructions only used to calculate that store
	if (Instruction* D = dyn_cast<Instruction>(dependency->getOperand(0)))
	possiblyDead.insert(D);

	dependency->eraseFromParent();
	NumFastStores++;
	return true;
	}

	return false;
	}

	/// handleEndBlock - Remove dead stores to stack-allocated locations in the function
	/// end block
	bool FDSE::handleEndBlock(BasicBlock& BB, SetVector<Instruction*>& possiblyDead) {
	AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
	MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();

	bool MadeChange = false;

	// Pointers alloca'd in this function are dead in the end block
	SmallPtrSet<AllocaInst*, 4> deadPointers;

	// Find all of the alloca'd pointers in the entry block
	BasicBlock *Entry = BB.getParent()->begin();
	for (BasicBlock::iterator I = Entry->begin(), E = Entry->end(); I != E; ++I)
	if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
	deadPointers.insert(AI);

	// Scan the basic block backwards
	for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
	--BBI;

	if (deadPointers.empty())
	break;

	// If we find a store whose pointer is dead...
	if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
	if (deadPointers.count(S->getPointerOperand())){
	// Remove it!
	MD.removeInstruction(S);
	AA.deleteValue(S);

	// DCE instructions only used to calculate that store
	if (Instruction* D = dyn_cast<Instruction>(S->getOperand(0)))
	possiblyDead.insert(D);

	BBI++;
	S->eraseFromParent();
	NumFastStores++;
	MadeChange = true;
	}

	// If we encounter a use of the pointer, it is no longer considered dead
	} else if (LoadInst* L = dyn_cast<LoadInst>(BBI)) {
	deadPointers.erase(L->getPointerOperand());
	} else if (VAArgInst* V = dyn_cast<VAArgInst>(BBI)) {
	deadPointers.erase(V->getOperand(0));
	}
	}

	return MadeChange;
	}

	void FDSE::DeleteDeadInstructionChains(Instruction *I,
	SetVector<Instruction*> &DeadInsts) {
	// Instruction must be dead.
	if (!I->use_empty() \|\| !isInstructionTriviallyDead(I)) return;

	// Let the memory dependence know
	getAnalysis<MemoryDependenceAnalysis>().removeInstruction(I);
	getAnalysis<AliasAnalysis>().deleteValue(I);

	// See if this made any operands dead. We do it this way in case the
	// instruction uses the same operand twice. We don't want to delete a
	// 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.
	}

	I->eraseFromParent();
	++NumFastOther;
	}