diff options
Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp | 678 |
1 files changed, 678 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/contrib/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp new file mode 100644 index 0000000..2f1ae00 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp @@ -0,0 +1,678 @@ +//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This family of functions perform manipulations on basic blocks, and +// instructions contained within basic blocks. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Function.h" +#include "llvm/Instructions.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/Constant.h" +#include "llvm/Type.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Target/TargetData.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/ValueHandle.h" +#include <algorithm> +using namespace llvm; + +/// DeleteDeadBlock - Delete the specified block, which must have no +/// predecessors. +void llvm::DeleteDeadBlock(BasicBlock *BB) { + assert((pred_begin(BB) == pred_end(BB) || + // Can delete self loop. + BB->getSinglePredecessor() == BB) && "Block is not dead!"); + TerminatorInst *BBTerm = BB->getTerminator(); + + // Loop through all of our successors and make sure they know that one + // of their predecessors is going away. + for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) + BBTerm->getSuccessor(i)->removePredecessor(BB); + + // Zap all the instructions in the block. + while (!BB->empty()) { + Instruction &I = BB->back(); + // If this instruction is used, replace uses with an arbitrary value. + // Because control flow can't get here, we don't care what we replace the + // value with. Note that since this block is unreachable, and all values + // contained within it must dominate their uses, that all uses will + // eventually be removed (they are themselves dead). + if (!I.use_empty()) + I.replaceAllUsesWith(UndefValue::get(I.getType())); + BB->getInstList().pop_back(); + } + + // Zap the block! + BB->eraseFromParent(); +} + +/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are +/// any single-entry PHI nodes in it, fold them away. This handles the case +/// when all entries to the PHI nodes in a block are guaranteed equal, such as +/// when the block has exactly one predecessor. +void llvm::FoldSingleEntryPHINodes(BasicBlock *BB) { + while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { + if (PN->getIncomingValue(0) != PN) + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + else + PN->replaceAllUsesWith(UndefValue::get(PN->getType())); + PN->eraseFromParent(); + } +} + + +/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it +/// is dead. Also recursively delete any operands that become dead as +/// a result. This includes tracing the def-use list from the PHI to see if +/// it is ultimately unused or if it reaches an unused cycle. +bool llvm::DeleteDeadPHIs(BasicBlock *BB) { + // Recursively deleting a PHI may cause multiple PHIs to be deleted + // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete. + SmallVector<WeakVH, 8> PHIs; + for (BasicBlock::iterator I = BB->begin(); + PHINode *PN = dyn_cast<PHINode>(I); ++I) + PHIs.push_back(PN); + + bool Changed = false; + for (unsigned i = 0, e = PHIs.size(); i != e; ++i) + if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*())) + Changed |= RecursivelyDeleteDeadPHINode(PN); + + return Changed; +} + +/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, +/// if possible. The return value indicates success or failure. +bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) { + pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); + // Can't merge the entry block. Don't merge away blocks who have their + // address taken: this is a bug if the predecessor block is the entry node + // (because we'd end up taking the address of the entry) and undesirable in + // any case. + if (pred_begin(BB) == pred_end(BB) || + BB->hasAddressTaken()) return false; + + BasicBlock *PredBB = *PI++; + for (; PI != PE; ++PI) // Search all predecessors, see if they are all same + if (*PI != PredBB) { + PredBB = 0; // There are multiple different predecessors... + break; + } + + // Can't merge if there are multiple predecessors. + if (!PredBB) return false; + // Don't break self-loops. + if (PredBB == BB) return false; + // Don't break invokes. + if (isa<InvokeInst>(PredBB->getTerminator())) return false; + + succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); + BasicBlock* OnlySucc = BB; + for (; SI != SE; ++SI) + if (*SI != OnlySucc) { + OnlySucc = 0; // There are multiple distinct successors! + break; + } + + // Can't merge if there are multiple successors. + if (!OnlySucc) return false; + + // Can't merge if there is PHI loop. + for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { + if (PHINode *PN = dyn_cast<PHINode>(BI)) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + if (PN->getIncomingValue(i) == PN) + return false; + } else + break; + } + + // Begin by getting rid of unneeded PHIs. + while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + BB->getInstList().pop_front(); // Delete the phi node... + } + + // Delete the unconditional branch from the predecessor... + PredBB->getInstList().pop_back(); + + // Move all definitions in the successor to the predecessor... + PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); + + // Make all PHI nodes that referred to BB now refer to Pred as their + // source... + BB->replaceAllUsesWith(PredBB); + + // Inherit predecessors name if it exists. + if (!PredBB->hasName()) + PredBB->takeName(BB); + + // Finally, erase the old block and update dominator info. + if (P) { + if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) { + DomTreeNode* DTN = DT->getNode(BB); + DomTreeNode* PredDTN = DT->getNode(PredBB); + + if (DTN) { + SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); + for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(), + DE = Children.end(); DI != DE; ++DI) + DT->changeImmediateDominator(*DI, PredDTN); + + DT->eraseNode(BB); + } + } + } + + BB->eraseFromParent(); + + + return true; +} + +/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) +/// with a value, then remove and delete the original instruction. +/// +void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, + BasicBlock::iterator &BI, Value *V) { + Instruction &I = *BI; + // Replaces all of the uses of the instruction with uses of the value + I.replaceAllUsesWith(V); + + // Make sure to propagate a name if there is one already. + if (I.hasName() && !V->hasName()) + V->takeName(&I); + + // Delete the unnecessary instruction now... + BI = BIL.erase(BI); +} + + +/// ReplaceInstWithInst - Replace the instruction specified by BI with the +/// instruction specified by I. The original instruction is deleted and BI is +/// updated to point to the new instruction. +/// +void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, + BasicBlock::iterator &BI, Instruction *I) { + assert(I->getParent() == 0 && + "ReplaceInstWithInst: Instruction already inserted into basic block!"); + + // Insert the new instruction into the basic block... + BasicBlock::iterator New = BIL.insert(BI, I); + + // Replace all uses of the old instruction, and delete it. + ReplaceInstWithValue(BIL, BI, I); + + // Move BI back to point to the newly inserted instruction + BI = New; +} + +/// ReplaceInstWithInst - Replace the instruction specified by From with the +/// instruction specified by To. +/// +void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { + BasicBlock::iterator BI(From); + ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); +} + +/// RemoveSuccessor - Change the specified terminator instruction such that its +/// successor SuccNum no longer exists. Because this reduces the outgoing +/// degree of the current basic block, the actual terminator instruction itself +/// may have to be changed. In the case where the last successor of the block +/// is deleted, a return instruction is inserted in its place which can cause a +/// surprising change in program behavior if it is not expected. +/// +void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { + assert(SuccNum < TI->getNumSuccessors() && + "Trying to remove a nonexistant successor!"); + + // If our old successor block contains any PHI nodes, remove the entry in the + // PHI nodes that comes from this branch... + // + BasicBlock *BB = TI->getParent(); + TI->getSuccessor(SuccNum)->removePredecessor(BB); + + TerminatorInst *NewTI = 0; + switch (TI->getOpcode()) { + case Instruction::Br: + // If this is a conditional branch... convert to unconditional branch. + if (TI->getNumSuccessors() == 2) { + cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); + } else { // Otherwise convert to a return instruction... + Value *RetVal = 0; + + // Create a value to return... if the function doesn't return null... + if (!BB->getParent()->getReturnType()->isVoidTy()) + RetVal = Constant::getNullValue(BB->getParent()->getReturnType()); + + // Create the return... + NewTI = ReturnInst::Create(TI->getContext(), RetVal); + } + break; + + case Instruction::Invoke: // Should convert to call + case Instruction::Switch: // Should remove entry + default: + case Instruction::Ret: // Cannot happen, has no successors! + llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!"); + } + + if (NewTI) // If it's a different instruction, replace. + ReplaceInstWithInst(TI, NewTI); +} + +/// GetSuccessorNumber - Search for the specified successor of basic block BB +/// and return its position in the terminator instruction's list of +/// successors. It is an error to call this with a block that is not a +/// successor. +unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) { + TerminatorInst *Term = BB->getTerminator(); +#ifndef NDEBUG + unsigned e = Term->getNumSuccessors(); +#endif + for (unsigned i = 0; ; ++i) { + assert(i != e && "Didn't find edge?"); + if (Term->getSuccessor(i) == Succ) + return i; + } + return 0; +} + +/// SplitEdge - Split the edge connecting specified block. Pass P must +/// not be NULL. +BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { + unsigned SuccNum = GetSuccessorNumber(BB, Succ); + + // If this is a critical edge, let SplitCriticalEdge do it. + TerminatorInst *LatchTerm = BB->getTerminator(); + if (SplitCriticalEdge(LatchTerm, SuccNum, P)) + return LatchTerm->getSuccessor(SuccNum); + + // If the edge isn't critical, then BB has a single successor or Succ has a + // single pred. Split the block. + BasicBlock::iterator SplitPoint; + if (BasicBlock *SP = Succ->getSinglePredecessor()) { + // If the successor only has a single pred, split the top of the successor + // block. + assert(SP == BB && "CFG broken"); + SP = NULL; + return SplitBlock(Succ, Succ->begin(), P); + } else { + // Otherwise, if BB has a single successor, split it at the bottom of the + // block. + assert(BB->getTerminator()->getNumSuccessors() == 1 && + "Should have a single succ!"); + return SplitBlock(BB, BB->getTerminator(), P); + } +} + +/// SplitBlock - Split the specified block at the specified instruction - every +/// thing before SplitPt stays in Old and everything starting with SplitPt moves +/// to a new block. The two blocks are joined by an unconditional branch and +/// the loop info is updated. +/// +BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { + BasicBlock::iterator SplitIt = SplitPt; + while (isa<PHINode>(SplitIt)) + ++SplitIt; + BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); + + // The new block lives in whichever loop the old one did. This preserves + // LCSSA as well, because we force the split point to be after any PHI nodes. + if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>()) + if (Loop *L = LI->getLoopFor(Old)) + L->addBasicBlockToLoop(New, LI->getBase()); + + if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) { + // Old dominates New. New node domiantes all other nodes dominated by Old. + DomTreeNode *OldNode = DT->getNode(Old); + std::vector<DomTreeNode *> Children; + for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); + I != E; ++I) + Children.push_back(*I); + + DomTreeNode *NewNode = DT->addNewBlock(New,Old); + for (std::vector<DomTreeNode *>::iterator I = Children.begin(), + E = Children.end(); I != E; ++I) + DT->changeImmediateDominator(*I, NewNode); + } + + if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>()) + DF->splitBlock(Old); + + return New; +} + + +/// SplitBlockPredecessors - This method transforms BB by introducing a new +/// basic block into the function, and moving some of the predecessors of BB to +/// be predecessors of the new block. The new predecessors are indicated by the +/// Preds array, which has NumPreds elements in it. The new block is given a +/// suffix of 'Suffix'. +/// +/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, +/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. +/// In particular, it does not preserve LoopSimplify (because it's +/// complicated to handle the case where one of the edges being split +/// is an exit of a loop with other exits). +/// +BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, + BasicBlock *const *Preds, + unsigned NumPreds, const char *Suffix, + Pass *P) { + // Create new basic block, insert right before the original block. + BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix, + BB->getParent(), BB); + + // The new block unconditionally branches to the old block. + BranchInst *BI = BranchInst::Create(BB, NewBB); + + LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0; + Loop *L = LI ? LI->getLoopFor(BB) : 0; + bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); + + // Move the edges from Preds to point to NewBB instead of BB. + // While here, if we need to preserve loop analyses, collect + // some information about how this split will affect loops. + bool HasLoopExit = false; + bool IsLoopEntry = !!L; + bool SplitMakesNewLoopHeader = false; + for (unsigned i = 0; i != NumPreds; ++i) { + // This is slightly more strict than necessary; the minimum requirement + // is that there be no more than one indirectbr branching to BB. And + // all BlockAddress uses would need to be updated. + assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && + "Cannot split an edge from an IndirectBrInst"); + + Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); + + if (LI) { + // If we need to preserve LCSSA, determine if any of + // the preds is a loop exit. + if (PreserveLCSSA) + if (Loop *PL = LI->getLoopFor(Preds[i])) + if (!PL->contains(BB)) + HasLoopExit = true; + // If we need to preserve LoopInfo, note whether any of the + // preds crosses an interesting loop boundary. + if (L) { + if (L->contains(Preds[i])) + IsLoopEntry = false; + else + SplitMakesNewLoopHeader = true; + } + } + } + + // Update dominator tree and dominator frontier if available. + DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0; + if (DT) + DT->splitBlock(NewBB); + if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0) + DF->splitBlock(NewBB); + + // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI + // node becomes an incoming value for BB's phi node. However, if the Preds + // list is empty, we need to insert dummy entries into the PHI nodes in BB to + // account for the newly created predecessor. + if (NumPreds == 0) { + // Insert dummy values as the incoming value. + for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) + cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); + return NewBB; + } + + AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; + + if (L) { + if (IsLoopEntry) { + // Add the new block to the nearest enclosing loop (and not an + // adjacent loop). To find this, examine each of the predecessors and + // determine which loops enclose them, and select the most-nested loop + // which contains the loop containing the block being split. + Loop *InnermostPredLoop = 0; + for (unsigned i = 0; i != NumPreds; ++i) + if (Loop *PredLoop = LI->getLoopFor(Preds[i])) { + // Seek a loop which actually contains the block being split (to + // avoid adjacent loops). + while (PredLoop && !PredLoop->contains(BB)) + PredLoop = PredLoop->getParentLoop(); + // Select the most-nested of these loops which contains the block. + if (PredLoop && + PredLoop->contains(BB) && + (!InnermostPredLoop || + InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth())) + InnermostPredLoop = PredLoop; + } + if (InnermostPredLoop) + InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase()); + } else { + L->addBasicBlockToLoop(NewBB, LI->getBase()); + if (SplitMakesNewLoopHeader) + L->moveToHeader(NewBB); + } + } + + // Otherwise, create a new PHI node in NewBB for each PHI node in BB. + for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { + PHINode *PN = cast<PHINode>(I++); + + // Check to see if all of the values coming in are the same. If so, we + // don't need to create a new PHI node, unless it's needed for LCSSA. + Value *InVal = 0; + if (!HasLoopExit) { + InVal = PN->getIncomingValueForBlock(Preds[0]); + for (unsigned i = 1; i != NumPreds; ++i) + if (InVal != PN->getIncomingValueForBlock(Preds[i])) { + InVal = 0; + break; + } + } + + if (InVal) { + // If all incoming values for the new PHI would be the same, just don't + // make a new PHI. Instead, just remove the incoming values from the old + // PHI. + for (unsigned i = 0; i != NumPreds; ++i) + PN->removeIncomingValue(Preds[i], false); + } else { + // If the values coming into the block are not the same, we need a PHI. + // Create the new PHI node, insert it into NewBB at the end of the block + PHINode *NewPHI = + PHINode::Create(PN->getType(), PN->getName()+".ph", BI); + if (AA) AA->copyValue(PN, NewPHI); + + // Move all of the PHI values for 'Preds' to the new PHI. + for (unsigned i = 0; i != NumPreds; ++i) { + Value *V = PN->removeIncomingValue(Preds[i], false); + NewPHI->addIncoming(V, Preds[i]); + } + InVal = NewPHI; + } + + // Add an incoming value to the PHI node in the loop for the preheader + // edge. + PN->addIncoming(InVal, NewBB); + } + + return NewBB; +} + +/// FindFunctionBackedges - Analyze the specified function to find all of the +/// loop backedges in the function and return them. This is a relatively cheap +/// (compared to computing dominators and loop info) analysis. +/// +/// The output is added to Result, as pairs of <from,to> edge info. +void llvm::FindFunctionBackedges(const Function &F, + SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) { + const BasicBlock *BB = &F.getEntryBlock(); + if (succ_begin(BB) == succ_end(BB)) + return; + + SmallPtrSet<const BasicBlock*, 8> Visited; + SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack; + SmallPtrSet<const BasicBlock*, 8> InStack; + + Visited.insert(BB); + VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); + InStack.insert(BB); + do { + std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back(); + const BasicBlock *ParentBB = Top.first; + succ_const_iterator &I = Top.second; + + bool FoundNew = false; + while (I != succ_end(ParentBB)) { + BB = *I++; + if (Visited.insert(BB)) { + FoundNew = true; + break; + } + // Successor is in VisitStack, it's a back edge. + if (InStack.count(BB)) + Result.push_back(std::make_pair(ParentBB, BB)); + } + + if (FoundNew) { + // Go down one level if there is a unvisited successor. + InStack.insert(BB); + VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); + } else { + // Go up one level. + InStack.erase(VisitStack.pop_back_val().first); + } + } while (!VisitStack.empty()); + + +} + + + +/// AreEquivalentAddressValues - Test if A and B will obviously have the same +/// value. This includes recognizing that %t0 and %t1 will have the same +/// value in code like this: +/// %t0 = getelementptr \@a, 0, 3 +/// store i32 0, i32* %t0 +/// %t1 = getelementptr \@a, 0, 3 +/// %t2 = load i32* %t1 +/// +static bool AreEquivalentAddressValues(const Value *A, const Value *B) { + // Test if the values are trivially equivalent. + if (A == B) return true; + + // Test if the values come from identical arithmetic instructions. + // Use isIdenticalToWhenDefined instead of isIdenticalTo because + // this function is only used when one address use dominates the + // other, which means that they'll always either have the same + // value or one of them will have an undefined value. + if (isa<BinaryOperator>(A) || isa<CastInst>(A) || + isa<PHINode>(A) || isa<GetElementPtrInst>(A)) + if (const Instruction *BI = dyn_cast<Instruction>(B)) + if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI)) + return true; + + // Otherwise they may not be equivalent. + return false; +} + +/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the +/// instruction before ScanFrom) checking to see if we have the value at the +/// memory address *Ptr locally available within a small number of instructions. +/// If the value is available, return it. +/// +/// If not, return the iterator for the last validated instruction that the +/// value would be live through. If we scanned the entire block and didn't find +/// something that invalidates *Ptr or provides it, ScanFrom would be left at +/// begin() and this returns null. ScanFrom could also be left +/// +/// MaxInstsToScan specifies the maximum instructions to scan in the block. If +/// it is set to 0, it will scan the whole block. You can also optionally +/// specify an alias analysis implementation, which makes this more precise. +Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, + BasicBlock::iterator &ScanFrom, + unsigned MaxInstsToScan, + AliasAnalysis *AA) { + if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; + + // If we're using alias analysis to disambiguate get the size of *Ptr. + unsigned AccessSize = 0; + if (AA) { + const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType(); + AccessSize = AA->getTypeStoreSize(AccessTy); + } + + while (ScanFrom != ScanBB->begin()) { + // We must ignore debug info directives when counting (otherwise they + // would affect codegen). + Instruction *Inst = --ScanFrom; + if (isa<DbgInfoIntrinsic>(Inst)) + continue; + + // Restore ScanFrom to expected value in case next test succeeds + ScanFrom++; + + // Don't scan huge blocks. + if (MaxInstsToScan-- == 0) return 0; + + --ScanFrom; + // If this is a load of Ptr, the loaded value is available. + if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) + if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) + return LI; + + if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + // If this is a store through Ptr, the value is available! + if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) + return SI->getOperand(0); + + // If Ptr is an alloca and this is a store to a different alloca, ignore + // the store. This is a trivial form of alias analysis that is important + // for reg2mem'd code. + if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) && + (isa<AllocaInst>(SI->getOperand(1)) || + isa<GlobalVariable>(SI->getOperand(1)))) + continue; + + // If we have alias analysis and it says the store won't modify the loaded + // value, ignore the store. + if (AA && + (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) + continue; + + // Otherwise the store that may or may not alias the pointer, bail out. + ++ScanFrom; + return 0; + } + + // If this is some other instruction that may clobber Ptr, bail out. + if (Inst->mayWriteToMemory()) { + // If alias analysis claims that it really won't modify the load, + // ignore it. + if (AA && + (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) + continue; + + // May modify the pointer, bail out. + ++ScanFrom; + return 0; + } + } + + // Got to the start of the block, we didn't find it, but are done for this + // block. + return 0; +} + |
