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AliasAnalysis, and some code for implementing the new query on top of existing implementations by making standard alias and getModRefInfo queries. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113329 91177308-0d34-0410-b5e6-96231b3b80d8
537 lines
19 KiB
C++
537 lines
19 KiB
C++
//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the generic AliasAnalysis interface which is used as the
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// common interface used by all clients and implementations of alias analysis.
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//
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// This file also implements the default version of the AliasAnalysis interface
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// that is to be used when no other implementation is specified. This does some
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// simple tests that detect obvious cases: two different global pointers cannot
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// alias, a global cannot alias a malloc, two different mallocs cannot alias,
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// etc.
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//
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// This alias analysis implementation really isn't very good for anything, but
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// it is very fast, and makes a nice clean default implementation. Because it
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// handles lots of little corner cases, other, more complex, alias analysis
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// implementations may choose to rely on this pass to resolve these simple and
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// easy cases.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Pass.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Function.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Target/TargetData.h"
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using namespace llvm;
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// Register the AliasAnalysis interface, providing a nice name to refer to.
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static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
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char AliasAnalysis::ID = 0;
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//===----------------------------------------------------------------------===//
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// Default chaining methods
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//===----------------------------------------------------------------------===//
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AliasAnalysis::AliasResult
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AliasAnalysis::alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->alias(V1, V1Size, V2, V2Size);
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}
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bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->pointsToConstantMemory(P);
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}
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void AliasAnalysis::deleteValue(Value *V) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->deleteValue(V);
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}
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void AliasAnalysis::copyValue(Value *From, Value *To) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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AA->copyValue(From, To);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(ImmutableCallSite CS,
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const Value *P, unsigned Size) {
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// Don't assert AA because BasicAA calls us in order to make use of the
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// logic here.
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ModRefBehavior MRB = getModRefBehavior(CS);
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if (MRB == DoesNotAccessMemory)
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return NoModRef;
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ModRefResult Mask = ModRef;
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if (MRB == OnlyReadsMemory)
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Mask = Ref;
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else if (MRB == AliasAnalysis::AccessesArguments) {
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bool doesAlias = false;
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for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
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AI != AE; ++AI)
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if (!isNoAlias(*AI, ~0U, P, Size)) {
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doesAlias = true;
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break;
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}
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if (!doesAlias)
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return NoModRef;
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}
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// If P points to a constant memory location, the call definitely could not
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// modify the memory location.
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if ((Mask & Mod) && pointsToConstantMemory(P))
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Mask = ModRefResult(Mask & ~Mod);
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// If this is BasicAA, don't forward.
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if (!AA) return Mask;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any mask we've managed to compute.
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return ModRefResult(AA->getModRefInfo(CS, P, Size) & Mask);
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
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// Don't assert AA because BasicAA calls us in order to make use of the
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// logic here.
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// If CS1 or CS2 are readnone, they don't interact.
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ModRefBehavior CS1B = getModRefBehavior(CS1);
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if (CS1B == DoesNotAccessMemory) return NoModRef;
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ModRefBehavior CS2B = getModRefBehavior(CS2);
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if (CS2B == DoesNotAccessMemory) return NoModRef;
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// If they both only read from memory, there is no dependence.
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if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
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return NoModRef;
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AliasAnalysis::ModRefResult Mask = ModRef;
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// If CS1 only reads memory, the only dependence on CS2 can be
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// from CS1 reading memory written by CS2.
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if (CS1B == OnlyReadsMemory)
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Mask = ModRefResult(Mask & Ref);
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// If CS2 only access memory through arguments, accumulate the mod/ref
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// information from CS1's references to the memory referenced by
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// CS2's arguments.
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if (CS2B == AccessesArguments) {
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AliasAnalysis::ModRefResult R = NoModRef;
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for (ImmutableCallSite::arg_iterator
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I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
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R = ModRefResult((R | getModRefInfo(CS1, *I, UnknownSize)) & Mask);
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if (R == Mask)
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break;
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}
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return R;
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}
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// If CS1 only accesses memory through arguments, check if CS2 references
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// any of the memory referenced by CS1's arguments. If not, return NoModRef.
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if (CS1B == AccessesArguments) {
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AliasAnalysis::ModRefResult R = NoModRef;
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for (ImmutableCallSite::arg_iterator
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I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I)
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if (getModRefInfo(CS2, *I, UnknownSize) != NoModRef) {
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R = Mask;
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break;
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}
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if (R == NoModRef)
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return R;
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}
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// If this is BasicAA, don't forward.
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if (!AA) return Mask;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any mask we've managed to compute.
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return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask);
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
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// Don't assert AA because BasicAA calls us in order to make use of the
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// logic here.
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ModRefBehavior Min = UnknownModRefBehavior;
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// Call back into the alias analysis with the other form of getModRefBehavior
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// to see if it can give a better response.
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if (const Function *F = CS.getCalledFunction())
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Min = getModRefBehavior(F);
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// If this is BasicAA, don't forward.
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if (!AA) return Min;
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// Otherwise, fall back to the next AA in the chain. But we can merge
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// in any result we've managed to compute.
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return std::min(AA->getModRefBehavior(CS), Min);
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getModRefBehavior(const Function *F) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getModRefBehavior(F);
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}
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AliasAnalysis::DependenceResult
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AliasAnalysis::getDependence(const Instruction *First,
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DependenceQueryFlags FirstFlags,
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const Instruction *Second,
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DependenceQueryFlags SecondFlags) {
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assert(AA && "AA didn't call InitializeAliasAnalyais in its run method!");
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return AA->getDependence(First, FirstFlags, Second, SecondFlags);
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}
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//===----------------------------------------------------------------------===//
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// AliasAnalysis non-virtual helper method implementation
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//===----------------------------------------------------------------------===//
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const LoadInst *L, const Value *P, unsigned Size) {
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// Be conservative in the face of volatile.
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if (L->isVolatile())
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return ModRef;
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// If the load address doesn't alias the given address, it doesn't read
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// or write the specified memory.
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if (!alias(L->getOperand(0), getTypeStoreSize(L->getType()), P, Size))
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return NoModRef;
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// Otherwise, a load just reads.
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return Ref;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const StoreInst *S, const Value *P, unsigned Size) {
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// Be conservative in the face of volatile.
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if (S->isVolatile())
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return ModRef;
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// If the store address cannot alias the pointer in question, then the
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// specified memory cannot be modified by the store.
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if (!alias(S->getOperand(1),
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getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
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return NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have been
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// modified by this store.
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if (pointsToConstantMemory(P))
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return NoModRef;
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// Otherwise, a store just writes.
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return Mod;
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}
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AliasAnalysis::ModRefResult
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AliasAnalysis::getModRefInfo(const VAArgInst *V, const Value *P, unsigned Size) {
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// If the va_arg address cannot alias the pointer in question, then the
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// specified memory cannot be accessed by the va_arg.
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if (!alias(V->getOperand(0), UnknownSize, P, Size))
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return NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have been
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// modified by this va_arg.
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if (pointsToConstantMemory(P))
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return NoModRef;
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// Otherwise, a va_arg reads and writes.
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return ModRef;
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}
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AliasAnalysis::DependenceResult
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AliasAnalysis::getDependenceViaModRefInfo(const Instruction *First,
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DependenceQueryFlags FirstFlags,
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const Instruction *Second,
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DependenceQueryFlags SecondFlags) {
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if (const LoadInst *L = dyn_cast<LoadInst>(First)) {
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// Be over-conservative with volatile for now.
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if (L->isVolatile())
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return Unknown;
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// Forward this query to getModRefInfo.
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switch (getModRefInfo(Second,
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L->getPointerOperand(),
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getTypeStoreSize(L->getType()))) {
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case NoModRef:
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// Second doesn't reference First's memory, so they're independent.
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return Independent;
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case Ref:
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// Second only reads from the memory read from by First. If it
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// also writes to any other memory, be conservative.
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if (Second->mayWriteToMemory())
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return Unknown;
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// If it's loading the same size from the same address, we can
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// give a more precise result.
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if (const LoadInst *SecondL = dyn_cast<LoadInst>(Second)) {
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unsigned LSize = getTypeStoreSize(L->getType());
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unsigned SecondLSize = getTypeStoreSize(SecondL->getType());
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if (alias(L->getPointerOperand(), LSize,
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SecondL->getPointerOperand(), SecondLSize) ==
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MustAlias) {
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// If the loads are the same size, it's ReadThenRead.
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if (LSize == SecondLSize)
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return ReadThenRead;
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// If the second load is smaller, it's only ReadThenReadSome.
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if (LSize > SecondLSize)
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return ReadThenReadSome;
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}
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}
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// Otherwise it's just two loads.
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return Independent;
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case Mod:
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// Second only writes to the memory read from by First. If it
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// also reads from any other memory, be conservative.
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if (Second->mayReadFromMemory())
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return Unknown;
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// If it's storing the same size to the same address, we can
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// give a more precise result.
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if (const StoreInst *SecondS = dyn_cast<StoreInst>(Second)) {
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unsigned LSize = getTypeStoreSize(L->getType());
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unsigned SecondSSize = getTypeStoreSize(SecondS->getType());
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if (alias(L->getPointerOperand(), LSize,
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SecondS->getPointerOperand(), SecondSSize) ==
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MustAlias) {
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// If the load and the store are the same size, it's ReadThenWrite.
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if (LSize == SecondSSize)
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return ReadThenWrite;
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}
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}
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// Otherwise we don't know if it could be writing to other memory.
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return Unknown;
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case ModRef:
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// Second reads and writes to the memory read from by First.
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// We don't have a way to express that.
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return Unknown;
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}
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} else if (const StoreInst *S = dyn_cast<StoreInst>(First)) {
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// Be over-conservative with volatile for now.
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if (S->isVolatile())
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return Unknown;
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// Forward this query to getModRefInfo.
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switch (getModRefInfo(Second,
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S->getPointerOperand(),
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getTypeStoreSize(S->getValueOperand()->getType()))) {
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case NoModRef:
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// Second doesn't reference First's memory, so they're independent.
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return Independent;
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case Ref:
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// Second only reads from the memory written to by First. If it
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// also writes to any other memory, be conservative.
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if (Second->mayWriteToMemory())
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return Unknown;
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// If it's loading the same size from the same address, we can
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// give a more precise result.
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if (const LoadInst *SecondL = dyn_cast<LoadInst>(Second)) {
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unsigned SSize = getTypeStoreSize(S->getValueOperand()->getType());
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unsigned SecondLSize = getTypeStoreSize(SecondL->getType());
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if (alias(S->getPointerOperand(), SSize,
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SecondL->getPointerOperand(), SecondLSize) ==
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MustAlias) {
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// If the store and the load are the same size, it's WriteThenRead.
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if (SSize == SecondLSize)
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return WriteThenRead;
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// If the load is smaller, it's only WriteThenReadSome.
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if (SSize > SecondLSize)
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return WriteThenReadSome;
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}
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}
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// Otherwise we don't know if it could be reading from other memory.
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return Unknown;
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case Mod:
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// Second only writes to the memory written to by First. If it
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// also reads from any other memory, be conservative.
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if (Second->mayReadFromMemory())
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return Unknown;
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// If it's storing the same size to the same address, we can
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// give a more precise result.
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if (const StoreInst *SecondS = dyn_cast<StoreInst>(Second)) {
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unsigned SSize = getTypeStoreSize(S->getValueOperand()->getType());
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unsigned SecondSSize = getTypeStoreSize(SecondS->getType());
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if (alias(S->getPointerOperand(), SSize,
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SecondS->getPointerOperand(), SecondSSize) ==
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MustAlias) {
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// If the stores are the same size, it's WriteThenWrite.
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if (SSize == SecondSSize)
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return WriteThenWrite;
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// If the second store is larger, it's only WriteSomeThenWrite.
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if (SSize < SecondSSize)
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return WriteSomeThenWrite;
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}
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}
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// Otherwise we don't know if it could be writing to other memory.
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return Unknown;
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case ModRef:
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// Second reads and writes to the memory written to by First.
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// We don't have a way to express that.
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return Unknown;
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}
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} else if (const VAArgInst *V = dyn_cast<VAArgInst>(First)) {
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// Forward this query to getModRefInfo.
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if (getModRefInfo(Second, V->getOperand(0), UnknownSize) == NoModRef)
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// Second doesn't reference First's memory, so they're independent.
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return Independent;
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} else if (ImmutableCallSite FirstCS = cast<Value>(First)) {
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// If both instructions are calls/invokes we can use the two-callsite
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// form of getModRefInfo.
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if (ImmutableCallSite SecondCS = cast<Value>(Second))
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// getModRefInfo's arguments are backwards from intuition.
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switch (getModRefInfo(SecondCS, FirstCS)) {
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case NoModRef:
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// Second doesn't reference First's memory, so they're independent.
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return Independent;
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case Ref:
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// If they're both read-only, there's no dependence.
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if (FirstCS.onlyReadsMemory() && SecondCS.onlyReadsMemory())
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return Independent;
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// Otherwise it's not obvious what we can do here.
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return Unknown;
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case Mod:
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// It's not obvious what we can do here.
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return Unknown;
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case ModRef:
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// I know, right?
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return Unknown;
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}
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}
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// For anything else, be conservative.
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return Unknown;
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}
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AliasAnalysis::ModRefBehavior
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AliasAnalysis::getIntrinsicModRefBehavior(unsigned iid) {
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#define GET_INTRINSIC_MODREF_BEHAVIOR
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#include "llvm/Intrinsics.gen"
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#undef GET_INTRINSIC_MODREF_BEHAVIOR
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}
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// AliasAnalysis destructor: DO NOT move this to the header file for
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// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
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// the AliasAnalysis.o file in the current .a file, causing alias analysis
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// support to not be included in the tool correctly!
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//
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AliasAnalysis::~AliasAnalysis() {}
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/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
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/// AliasAnalysis interface before any other methods are called.
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///
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void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
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TD = P->getAnalysisIfAvailable<TargetData>();
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AA = &P->getAnalysis<AliasAnalysis>();
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}
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// getAnalysisUsage - All alias analysis implementations should invoke this
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// directly (using AliasAnalysis::getAnalysisUsage(AU)).
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void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AliasAnalysis>(); // All AA's chain
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}
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/// getTypeStoreSize - Return the TargetData store size for the given type,
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/// if known, or a conservative value otherwise.
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///
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unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) {
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return TD ? TD->getTypeStoreSize(Ty) : ~0u;
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}
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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the value pointed to by Ptr.
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///
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bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
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const Value *Ptr, unsigned Size) {
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return canInstructionRangeModify(BB.front(), BB.back(), Ptr, Size);
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}
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/// canInstructionRangeModify - Return true if it is possible for the execution
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/// of the specified instructions to modify the value pointed to by Ptr. The
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/// instructions to consider are all of the instructions in the range of [I1,I2]
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/// INCLUSIVE. I1 and I2 must be in the same basic block.
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///
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bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
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const Instruction &I2,
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const Value *Ptr, unsigned Size) {
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assert(I1.getParent() == I2.getParent() &&
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"Instructions not in same basic block!");
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BasicBlock::const_iterator I = &I1;
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BasicBlock::const_iterator E = &I2;
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++E; // Convert from inclusive to exclusive range.
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for (; I != E; ++I) // Check every instruction in range
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if (getModRefInfo(I, Ptr, Size) & Mod)
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return true;
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return false;
|
|
}
|
|
|
|
/// isNoAliasCall - Return true if this pointer is returned by a noalias
|
|
/// function.
|
|
bool llvm::isNoAliasCall(const Value *V) {
|
|
if (isa<CallInst>(V) || isa<InvokeInst>(V))
|
|
return ImmutableCallSite(cast<Instruction>(V))
|
|
.paramHasAttr(0, Attribute::NoAlias);
|
|
return false;
|
|
}
|
|
|
|
/// isIdentifiedObject - Return true if this pointer refers to a distinct and
|
|
/// identifiable object. This returns true for:
|
|
/// Global Variables and Functions (but not Global Aliases)
|
|
/// Allocas and Mallocs
|
|
/// ByVal and NoAlias Arguments
|
|
/// NoAlias returns
|
|
///
|
|
bool llvm::isIdentifiedObject(const Value *V) {
|
|
if (isa<AllocaInst>(V))
|
|
return true;
|
|
if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
|
|
return true;
|
|
if (isNoAliasCall(V))
|
|
return true;
|
|
if (const Argument *A = dyn_cast<Argument>(V))
|
|
return A->hasNoAliasAttr() || A->hasByValAttr();
|
|
return false;
|
|
}
|
|
|
|
// Because of the way .a files work, we must force the BasicAA implementation to
|
|
// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
|
|
// the risk of AliasAnalysis being used, but the default implementation not
|
|
// being linked into the tool that uses it.
|
|
DEFINING_FILE_FOR(AliasAnalysis)
|