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163 lines
5.4 KiB
C++
163 lines
5.4 KiB
C++
//===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===//
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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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/// \file
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/// This file defines a simple ARC-aware AliasAnalysis using special knowledge
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/// of Objective C to enhance other optimization passes which rely on the Alias
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/// Analysis infrastructure.
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///
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/// WARNING: This file knows about certain library functions. It recognizes them
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/// by name, and hardwires knowledge of their semantics.
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///
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/// WARNING: This file knows about how certain Objective-C library functions are
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/// used. Naive LLVM IR transformations which would otherwise be
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/// behavior-preserving may break these assumptions.
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///
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "objc-arc-aa"
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#include "ObjCARC.h"
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#include "ObjCARCAliasAnalysis.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/PassAnalysisSupport.h"
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#include "llvm/PassSupport.h"
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namespace llvm {
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class Function;
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class Value;
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}
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using namespace llvm;
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using namespace llvm::objcarc;
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// Register this pass...
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char ObjCARCAliasAnalysis::ID = 0;
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INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
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"ObjC-ARC-Based Alias Analysis", false, true, false)
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ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
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return new ObjCARCAliasAnalysis();
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}
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void
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ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AliasAnalysis::getAnalysisUsage(AU);
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}
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AliasAnalysis::AliasResult
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ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) {
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if (!EnableARCOpts)
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return AliasAnalysis::alias(LocA, LocB);
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// First, strip off no-ops, including ObjC-specific no-ops, and try making a
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// precise alias query.
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const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr);
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const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr);
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AliasResult Result =
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AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag),
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Location(SB, LocB.Size, LocB.TBAATag));
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if (Result != MayAlias)
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return Result;
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// If that failed, climb to the underlying object, including climbing through
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// ObjC-specific no-ops, and try making an imprecise alias query.
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const Value *UA = GetUnderlyingObjCPtr(SA);
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const Value *UB = GetUnderlyingObjCPtr(SB);
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if (UA != SA || UB != SB) {
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Result = AliasAnalysis::alias(Location(UA), Location(UB));
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// We can't use MustAlias or PartialAlias results here because
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// GetUnderlyingObjCPtr may return an offsetted pointer value.
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if (Result == NoAlias)
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return NoAlias;
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}
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// If that failed, fail. We don't need to chain here, since that's covered
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// by the earlier precise query.
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return MayAlias;
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}
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bool
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ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc,
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bool OrLocal) {
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if (!EnableARCOpts)
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return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
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// First, strip off no-ops, including ObjC-specific no-ops, and try making
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// a precise alias query.
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const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr);
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if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag),
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OrLocal))
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return true;
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// If that failed, climb to the underlying object, including climbing through
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// ObjC-specific no-ops, and try making an imprecise alias query.
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const Value *U = GetUnderlyingObjCPtr(S);
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if (U != S)
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return AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal);
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// If that failed, fail. We don't need to chain here, since that's covered
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// by the earlier precise query.
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return false;
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}
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AliasAnalysis::ModRefBehavior
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ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
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// We have nothing to do. Just chain to the next AliasAnalysis.
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return AliasAnalysis::getModRefBehavior(CS);
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}
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AliasAnalysis::ModRefBehavior
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ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
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if (!EnableARCOpts)
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return AliasAnalysis::getModRefBehavior(F);
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switch (GetFunctionClass(F)) {
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case IC_NoopCast:
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return DoesNotAccessMemory;
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default:
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break;
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}
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return AliasAnalysis::getModRefBehavior(F);
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}
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AliasAnalysis::ModRefResult
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ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
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if (!EnableARCOpts)
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return AliasAnalysis::getModRefInfo(CS, Loc);
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switch (GetBasicInstructionClass(CS.getInstruction())) {
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case IC_Retain:
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case IC_RetainRV:
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case IC_Autorelease:
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case IC_AutoreleaseRV:
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case IC_NoopCast:
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case IC_AutoreleasepoolPush:
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case IC_FusedRetainAutorelease:
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case IC_FusedRetainAutoreleaseRV:
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// These functions don't access any memory visible to the compiler.
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// Note that this doesn't include objc_retainBlock, because it updates
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// pointers when it copies block data.
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return NoModRef;
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default:
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break;
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}
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return AliasAnalysis::getModRefInfo(CS, Loc);
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}
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AliasAnalysis::ModRefResult
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ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) {
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// TODO: Theoretically we could check for dependencies between objc_* calls
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// and OnlyAccessesArgumentPointees calls or other well-behaved calls.
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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}
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