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Diffstat (limited to 'lib/Analysis/LoadValueNumbering.cpp')
| -rw-r--r-- | lib/Analysis/LoadValueNumbering.cpp | 530 |
1 files changed, 0 insertions, 530 deletions
diff --git a/lib/Analysis/LoadValueNumbering.cpp b/lib/Analysis/LoadValueNumbering.cpp deleted file mode 100644 index f99ebb4a83..0000000000 --- a/lib/Analysis/LoadValueNumbering.cpp +++ /dev/null @@ -1,530 +0,0 @@ -//===- LoadValueNumbering.cpp - Load Value #'ing Implementation -*- C++ -*-===// -// -// 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 value numbering pass that value numbers load and call -// 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. To value number call instructions, it looks for calls to -// functions that do not write to memory which do not have intervening -// instructions that clobber the memory that is read from. -// -// This pass builds off of another value numbering pass to implement value -// numbering for non-load and non-call 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 value numbering will be. -// -//===----------------------------------------------------------------------===// - -#include "llvm/Analysis/LoadValueNumbering.h" -#include "llvm/Constants.h" -#include "llvm/Function.h" -#include "llvm/Instructions.h" -#include "llvm/Pass.h" -#include "llvm/Type.h" -#include "llvm/Analysis/ValueNumbering.h" -#include "llvm/Analysis/AliasAnalysis.h" -#include "llvm/Analysis/Dominators.h" -#include "llvm/Support/CFG.h" -#include "llvm/Support/Compiler.h" -#include "llvm/Target/TargetData.h" -#include <set> -#include <algorithm> -using namespace llvm; - -namespace { - // FIXME: This should not be a FunctionPass. - struct VISIBILITY_HIDDEN LoadVN : public FunctionPass, public ValueNumbering { - static char ID; // Class identification, replacement for typeinfo - LoadVN() : FunctionPass((intptr_t)&ID) {} - - /// 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; - - /// deleteValue - This method should be called whenever an LLVM Value is - /// deleted from the program, for example when an instruction is found to be - /// redundant and is eliminated. - /// - virtual void deleteValue(Value *V) { - getAnalysis<AliasAnalysis>().deleteValue(V); - } - - /// copyValue - This method should be used whenever a preexisting value in - /// the program is copied or cloned, introducing a new value. Note that - /// analysis implementations should tolerate clients that use this method to - /// introduce the same value multiple times: if the analysis already knows - /// about a value, it should ignore the request. - /// - virtual void copyValue(Value *From, Value *To) { - getAnalysis<AliasAnalysis>().copyValue(From, To); - } - - /// getCallEqualNumberNodes - Given a call instruction, find other calls - /// that have the same value number. - void getCallEqualNumberNodes(CallInst *CI, - std::vector<Value*> &RetVals) const; - }; -} - -char LoadVN::ID = 0; -// Register this pass... -static RegisterPass<LoadVN> -X("load-vn", "Load Value Numbering", false, true); - -// Declare that we implement the ValueNumbering interface -static RegisterAnalysisGroup<ValueNumbering> Y(X); - -FunctionPass *llvm::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.addRequiredTransitive<AliasAnalysis>(); - AU.addRequired<ValueNumbering>(); - AU.addRequiredTransitive<DominatorTree>(); - AU.addRequiredTransitive<TargetData>(); -} - -static bool isPathTransparentTo(BasicBlock *CurBlock, BasicBlock *Dom, - Value *Ptr, unsigned Size, AliasAnalysis &AA, - std::set<BasicBlock*> &Visited, - std::map<BasicBlock*, bool> &TransparentBlocks){ - // If we have already checked out this path, or if we reached our destination, - // stop searching, returning success. - if (CurBlock == Dom || !Visited.insert(CurBlock).second) - return true; - - // Check whether this block is known transparent or not. - std::map<BasicBlock*, bool>::iterator TBI = - TransparentBlocks.find(CurBlock); - - if (TBI == TransparentBlocks.end()) { - // If this basic block can modify the memory location, then the path is not - // transparent! - if (AA.canBasicBlockModify(*CurBlock, Ptr, Size)) { - TransparentBlocks.insert(TBI, std::make_pair(CurBlock, false)); - return false; - } - TransparentBlocks.insert(TBI, std::make_pair(CurBlock, true)); - } else if (!TBI->second) - // This block is known non-transparent, so that path can't be either. - return false; - - // The current block is known to be transparent. The entire path is - // transparent if all of the predecessors paths to the parent is also - // transparent to the memory location. - for (pred_iterator PI = pred_begin(CurBlock), E = pred_end(CurBlock); - PI != E; ++PI) - if (!isPathTransparentTo(*PI, Dom, Ptr, Size, AA, Visited, - TransparentBlocks)) - return false; - return true; -} - -/// getCallEqualNumberNodes - Given a call instruction, find other calls that -/// have the same value number. -void LoadVN::getCallEqualNumberNodes(CallInst *CI, - std::vector<Value*> &RetVals) const { - Function *CF = CI->getCalledFunction(); - if (CF == 0) return; // Indirect call. - AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); - AliasAnalysis::ModRefBehavior MRB = AA.getModRefBehavior(CI); - if (MRB != AliasAnalysis::DoesNotAccessMemory && - MRB != AliasAnalysis::OnlyReadsMemory) - return; // Nothing we can do for now. - - // Scan all of the arguments of the function, looking for one that is not - // global. In particular, we would prefer to have an argument or instruction - // operand to chase the def-use chains of. - Value *Op = CF; - for (User::op_iterator i = CI->op_begin() + 1, e = CI->op_end(); i != e; ++i) - if (isa<Argument>(*i) || - isa<Instruction>(*i)) { - Op = *i; - break; - } - - // Identify all lexically identical calls in this function. - std::vector<CallInst*> IdenticalCalls; - - Function *CIFunc = CI->getParent()->getParent(); - for (Value::use_iterator UI = Op->use_begin(), E = Op->use_end(); UI != E; - ++UI) - if (CallInst *C = dyn_cast<CallInst>(*UI)) - if (C->getNumOperands() == CI->getNumOperands() && - C->getOperand(0) == CI->getOperand(0) && - C->getParent()->getParent() == CIFunc && C != CI) { - bool AllOperandsEqual = true; - for (User::op_iterator i = CI->op_begin() + 1, j = C->op_begin() + 1, - e = CI->op_end(); i != e; ++i, ++j) - if (*j != *i) { - AllOperandsEqual = false; - break; - } - - if (AllOperandsEqual) - IdenticalCalls.push_back(C); - } - - if (IdenticalCalls.empty()) return; - - // Eliminate duplicates, which could occur if we chose a value that is passed - // into a call site multiple times. - std::sort(IdenticalCalls.begin(), IdenticalCalls.end()); - IdenticalCalls.erase(std::unique(IdenticalCalls.begin(),IdenticalCalls.end()), - IdenticalCalls.end()); - - // If the call reads memory, we must make sure that there are no stores - // between the calls in question. - // - // FIXME: This should use mod/ref information. What we really care about it - // whether an intervening instruction could modify memory that is read, not - // ANY memory. - // - if (MRB == AliasAnalysis::OnlyReadsMemory) { - DominatorTree &DT = getAnalysis<DominatorTree>(); - BasicBlock *CIBB = CI->getParent(); - for (unsigned i = 0; i != IdenticalCalls.size(); ++i) { - CallInst *C = IdenticalCalls[i]; - bool CantEqual = false; - - if (DT.dominates(CIBB, C->getParent())) { - // FIXME: we currently only handle the case where both calls are in the - // same basic block. - if (CIBB != C->getParent()) { - CantEqual = true; - } else { - Instruction *First = CI, *Second = C; - if (!DT.dominates(CI, C)) - std::swap(First, Second); - - // Scan the instructions between the calls, checking for stores or - // calls to dangerous functions. - BasicBlock::iterator I = First; - for (++First; I != BasicBlock::iterator(Second); ++I) { - if (isa<StoreInst>(I)) { - // FIXME: We could use mod/ref information to make this much - // better! - CantEqual = true; - break; - } else if (CallInst *CI = dyn_cast<CallInst>(I)) { - if (!AA.onlyReadsMemory(CI)) { - CantEqual = true; - break; - } - } else if (I->mayWriteToMemory()) { - CantEqual = true; - break; - } - } - } - - } else if (DT.dominates(C->getParent(), CIBB)) { - // FIXME: We could implement this, but we don't for now. - CantEqual = true; - } else { - // FIXME: if one doesn't dominate the other, we can't tell yet. - CantEqual = true; - } - - - if (CantEqual) { - // This call does not produce the same value as the one in the query. - std::swap(IdenticalCalls[i--], IdenticalCalls.back()); - IdenticalCalls.pop_back(); - } - } - } - - // Any calls that are identical and not destroyed will produce equal values! - for (unsigned i = 0, e = IdenticalCalls.size(); i != e; ++i) - RetVals.push_back(IdenticalCalls[i]); -} - -// 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 definitely use it. - if (isa<PointerType>(V->getType())) - getAnalysis<AliasAnalysis>().getMustAliases(V, RetVals); - - if (!isa<LoadInst>(V)) { - if (CallInst *CI = dyn_cast<CallInst>(V)) - getCallEqualNumberNodes(CI, RetVals); - - // Not a load instruction? Just chain to the base value numbering - // implementation to satisfy the request... - assert(&getAnalysis<ValueNumbering>() != (ValueNumbering*)this && - "getAnalysis() returned this!"); - - return getAnalysis<ValueNumbering>().getEqualNumberNodes(V, RetVals); - } - - // Volatile loads cannot be replaced with the value of other loads. - LoadInst *LI = cast<LoadInst>(V); - if (LI->isVolatile()) - return getAnalysis<ValueNumbering>().getEqualNumberNodes(V, RetVals); - - Value *LoadPtr = LI->getOperand(0); - BasicBlock *LoadBB = LI->getParent(); - Function *F = LoadBB->getParent(); - - // Find out how many bytes of memory are loaded by the load instruction... - unsigned LoadSize = getAnalysis<TargetData>().getTypeStoreSize(LI->getType()); - AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); - - // Figure out if the load is invalidated from the entry of the block it is in - // until the actual instruction. This scans the block backwards from LI. If - // we see any candidate load or store instructions, then we know that the - // candidates have the same value # as LI. - bool LoadInvalidatedInBBBefore = false; - for (BasicBlock::iterator I = LI; I != LoadBB->begin(); ) { - --I; - if (I == LoadPtr) { - // If we run into an allocation of the value being loaded, then the - // contents are not initialized. - if (isa<AllocationInst>(I)) - RetVals.push_back(UndefValue::get(LI->getType())); - - // Otherwise, since this is the definition of what we are loading, this - // loaded value cannot occur before this block. - LoadInvalidatedInBBBefore = true; - break; - } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) { - // If this instruction is a candidate load before LI, we know there are no - // invalidating instructions between it and LI, so they have the same - // value number. - if (LI->getOperand(0) == LoadPtr && !LI->isVolatile()) - RetVals.push_back(I); - } - - if (AA.getModRefInfo(I, LoadPtr, LoadSize) & AliasAnalysis::Mod) { - // If the invalidating instruction is a store, and its in our candidate - // set, then we can do store-load forwarding: the load has the same value - // # as the stored value. - if (StoreInst *SI = dyn_cast<StoreInst>(I)) - if (SI->getOperand(1) == LoadPtr) - RetVals.push_back(I->getOperand(0)); - - LoadInvalidatedInBBBefore = true; - break; - } - } - - // Figure out if the load is invalidated between the load and the exit of the - // block it is defined in. While we are scanning the current basic block, if - // we see any candidate loads, then we know they have the same value # as LI. - // - bool LoadInvalidatedInBBAfter = false; - { - BasicBlock::iterator I = LI; - for (++I; I != LoadBB->end(); ++I) { - // If this instruction is a load, then this instruction returns the same - // value as LI. - if (isa<LoadInst>(I) && cast<LoadInst>(I)->getOperand(0) == LoadPtr) - RetVals.push_back(I); - - if (AA.getModRefInfo(I, LoadPtr, LoadSize) & AliasAnalysis::Mod) { - LoadInvalidatedInBBAfter = true; - break; - } - } - } - - // If the pointer is clobbered on entry and on exit to the function, there is - // no need to do any global analysis at all. - if (LoadInvalidatedInBBBefore && LoadInvalidatedInBBAfter) - return; - - // Now that we know the value is not neccesarily killed on entry or exit to - // the BB, find out how many load and store instructions (to this location) - // live in each BB in the function. - // - std::map<BasicBlock*, unsigned> CandidateLoads; - std::set<BasicBlock*> CandidateStores; - - for (Value::use_iterator UI = LoadPtr->use_begin(), UE = LoadPtr->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? - // Not in LI's block? - Cand->getParent() != LoadBB && !Cand->isVolatile()) - ++CandidateLoads[Cand->getParent()]; // Got one. - } else if (StoreInst *Cand = dyn_cast<StoreInst>(*UI)) { - if (Cand->getParent()->getParent() == F && !Cand->isVolatile() && - Cand->getOperand(1) == LoadPtr) // It's a store THROUGH the ptr. - CandidateStores.insert(Cand->getParent()); - } - - // Get dominators. - DominatorTree &DT = getAnalysis<DominatorTree>(); - - // TransparentBlocks - For each basic block the load/store is alive across, - // figure out if the pointer is invalidated or not. If it is invalidated, the - // boolean is set to false, if it's not it is set to true. If we don't know - // yet, the entry is not in the map. - std::map<BasicBlock*, bool> TransparentBlocks; - - // Loop over all of the basic blocks that also load the value. If the value - // is live across the CFG from the source to destination blocks, and if the - // value is not invalidated in either the source or destination blocks, add it - // to the equivalence sets. - for (std::map<BasicBlock*, unsigned>::iterator - I = CandidateLoads.begin(), E = CandidateLoads.end(); I != E; ++I) { - bool CantEqual = false; - - // Right now we only can handle cases where one load dominates the other. - // FIXME: generalize this! - BasicBlock *BB1 = I->first, *BB2 = LoadBB; - if (DT.dominates(BB1, BB2)) { - // The other load dominates LI. If the loaded value is killed entering - // the LoadBB block, we know the load is not live. - if (LoadInvalidatedInBBBefore) - CantEqual = true; - } else if (DT.dominates(BB2, BB1)) { - std::swap(BB1, BB2); // Canonicalize - // LI dominates the other load. If the loaded value is killed exiting - // the LoadBB block, we know the load is not live. - if (LoadInvalidatedInBBAfter) - CantEqual = true; - } else { - // None of these loads can VN the same. - CantEqual = true; - } - - if (!CantEqual) { - // Ok, at this point, we know that BB1 dominates BB2, and that there is - // nothing in the LI block that kills the loaded value. Check to see if - // the value is live across the CFG. - std::set<BasicBlock*> Visited; - for (pred_iterator PI = pred_begin(BB2), E = pred_end(BB2); PI!=E; ++PI) - if (!isPathTransparentTo(*PI, BB1, LoadPtr, LoadSize, AA, - Visited, TransparentBlocks)) { - // None of these loads can VN the same. - CantEqual = true; - break; - } - } - - // If the loads can equal so far, scan the basic block that contains the - // loads under consideration to see if they are invalidated in the block. - // For any loads that are not invalidated, add them to the equivalence - // set! - if (!CantEqual) { - unsigned NumLoads = I->second; - if (BB1 == LoadBB) { - // If LI dominates the block in question, check to see if any of the - // loads in this block are invalidated before they are reached. - for (BasicBlock::iterator BBI = I->first->begin(); ; ++BBI) { - if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { - if (LI->getOperand(0) == LoadPtr && !LI->isVolatile()) { - // The load is in the set! - RetVals.push_back(BBI); - if (--NumLoads == 0) break; // Found last load to check. - } - } else if (AA.getModRefInfo(BBI, LoadPtr, LoadSize) - & AliasAnalysis::Mod) { - // If there is a modifying instruction, nothing below it will value - // # the same. - break; - } - } - } else { - // If the block dominates LI, make sure that the loads in the block are - // not invalidated before the block ends. - BasicBlock::iterator BBI = I->first->end(); - while (1) { - --BBI; - if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { - if (LI->getOperand(0) == LoadPtr && !LI->isVolatile()) { - // The load is the same as this load! - RetVals.push_back(BBI); - if (--NumLoads == 0) break; // Found all of the laods. - } - } else if (AA.getModRefInfo(BBI, LoadPtr, LoadSize) - & AliasAnalysis::Mod) { - // If there is a modifying instruction, nothing above it will value - // # the same. - break; - } - } - } - } - } - - // Handle candidate stores. If the loaded location is clobbered on entrance - // to the LoadBB, no store outside of the LoadBB can value number equal, so - // quick exit. - if (LoadInvalidatedInBBBefore) - return; - - // Stores in the load-bb are handled above. - CandidateStores.erase(LoadBB); - - for (std::set<BasicBlock*>::iterator I = CandidateStores.begin(), - E = CandidateStores.end(); I != E; ++I) - if (DT.dominates(*I, LoadBB)) { - BasicBlock *StoreBB = *I; - - // Check to see if the path from the store to the load is transparent - // w.r.t. the memory location. - bool CantEqual = false; - std::set<BasicBlock*> Visited; - for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); - PI != E; ++PI) - if (!isPathTransparentTo(*PI, StoreBB, LoadPtr, LoadSize, AA, - Visited, TransparentBlocks)) { - // None of these stores can VN the same. - CantEqual = true; - break; - } - Visited.clear(); - if (!CantEqual) { - // Okay, the path from the store block to the load block is clear, and - // we know that there are no invalidating instructions from the start - // of the load block to the load itself. Now we just scan the store - // block. - - BasicBlock::iterator BBI = StoreBB->end(); - while (1) { - assert(BBI != StoreBB->begin() && - "There is a store in this block of the pointer, but the store" - " doesn't mod the address being stored to?? Must be a bug in" - " the alias analysis implementation!"); - --BBI; - if (AA.getModRefInfo(BBI, LoadPtr, LoadSize) & AliasAnalysis::Mod) { - // If the invalidating instruction is one of the candidates, - // then it provides the value the load loads. - if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) - if (SI->getOperand(1) == LoadPtr) - RetVals.push_back(SI->getOperand(0)); - break; - } - } - } - } -} |