forked from OSchip/llvm-project
493 lines
18 KiB
C++
493 lines
18 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/Analysis/CFG.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Pass.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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INITIALIZE_ANALYSIS_GROUP(AliasAnalysis, "Alias Analysis", NoAA)
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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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AliasResult AliasAnalysis::alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->alias(LocA, LocB);
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}
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bool AliasAnalysis::pointsToConstantMemory(const MemoryLocation &Loc,
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bool OrLocal) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->pointsToConstantMemory(Loc, OrLocal);
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}
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ModRefInfo AliasAnalysis::getArgModRefInfo(ImmutableCallSite CS,
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unsigned ArgIdx) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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return AA->getArgModRefInfo(CS, ArgIdx);
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}
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ModRefInfo AliasAnalysis::getModRefInfo(Instruction *I,
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ImmutableCallSite Call) {
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// We may have two calls
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if (auto CS = ImmutableCallSite(I)) {
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// Check if the two calls modify the same memory
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return getModRefInfo(Call, CS);
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} else {
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// Otherwise, check if the call modifies or references the
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// location this memory access defines. The best we can say
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// is that if the call references what this instruction
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// defines, it must be clobbered by this location.
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const MemoryLocation DefLoc = MemoryLocation::get(I);
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if (getModRefInfo(Call, DefLoc) != MRI_NoModRef)
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return MRI_ModRef;
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}
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return MRI_NoModRef;
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}
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ModRefInfo AliasAnalysis::getModRefInfo(ImmutableCallSite CS,
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const MemoryLocation &Loc) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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auto MRB = getModRefBehavior(CS);
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if (MRB == FMRB_DoesNotAccessMemory)
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return MRI_NoModRef;
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ModRefInfo Mask = MRI_ModRef;
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if (onlyReadsMemory(MRB))
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Mask = MRI_Ref;
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if (onlyAccessesArgPointees(MRB)) {
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bool doesAlias = false;
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ModRefInfo AllArgsMask = MRI_NoModRef;
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if (doesAccessArgPointees(MRB)) {
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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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const Value *Arg = *AI;
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if (!Arg->getType()->isPointerTy())
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continue;
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unsigned ArgIdx = std::distance(CS.arg_begin(), AI);
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MemoryLocation ArgLoc =
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MemoryLocation::getForArgument(CS, ArgIdx, *TLI);
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if (!isNoAlias(ArgLoc, Loc)) {
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ModRefInfo ArgMask = getArgModRefInfo(CS, ArgIdx);
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doesAlias = true;
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AllArgsMask = ModRefInfo(AllArgsMask | ArgMask);
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}
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}
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}
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if (!doesAlias)
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return MRI_NoModRef;
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Mask = ModRefInfo(Mask & AllArgsMask);
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}
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// If Loc is a constant memory location, the call definitely could not
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// modify the memory location.
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if ((Mask & MRI_Mod) && pointsToConstantMemory(Loc))
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Mask = ModRefInfo(Mask & ~MRI_Mod);
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// If this is the end of the chain, 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 ModRefInfo(AA->getModRefInfo(CS, Loc) & Mask);
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}
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ModRefInfo AliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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// If CS1 or CS2 are readnone, they don't interact.
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auto CS1B = getModRefBehavior(CS1);
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if (CS1B == FMRB_DoesNotAccessMemory)
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return MRI_NoModRef;
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auto CS2B = getModRefBehavior(CS2);
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if (CS2B == FMRB_DoesNotAccessMemory)
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return MRI_NoModRef;
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// If they both only read from memory, there is no dependence.
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if (onlyReadsMemory(CS1B) && onlyReadsMemory(CS2B))
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return MRI_NoModRef;
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ModRefInfo Mask = MRI_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 (onlyReadsMemory(CS1B))
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Mask = ModRefInfo(Mask & MRI_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 (onlyAccessesArgPointees(CS2B)) {
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ModRefInfo R = MRI_NoModRef;
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if (doesAccessArgPointees(CS2B)) {
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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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const Value *Arg = *I;
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if (!Arg->getType()->isPointerTy())
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continue;
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unsigned CS2ArgIdx = std::distance(CS2.arg_begin(), I);
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auto CS2ArgLoc = MemoryLocation::getForArgument(CS2, CS2ArgIdx, *TLI);
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// ArgMask indicates what CS2 might do to CS2ArgLoc, and the dependence of
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// CS1 on that location is the inverse.
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ModRefInfo ArgMask = getArgModRefInfo(CS2, CS2ArgIdx);
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if (ArgMask == MRI_Mod)
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ArgMask = MRI_ModRef;
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else if (ArgMask == MRI_Ref)
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ArgMask = MRI_Mod;
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R = ModRefInfo((R | (getModRefInfo(CS1, CS2ArgLoc) & ArgMask)) & Mask);
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if (R == Mask)
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break;
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}
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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 (onlyAccessesArgPointees(CS1B)) {
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ModRefInfo R = MRI_NoModRef;
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if (doesAccessArgPointees(CS1B)) {
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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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const Value *Arg = *I;
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if (!Arg->getType()->isPointerTy())
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continue;
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unsigned CS1ArgIdx = std::distance(CS1.arg_begin(), I);
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auto CS1ArgLoc = MemoryLocation::getForArgument(CS1, CS1ArgIdx, *TLI);
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// ArgMask indicates what CS1 might do to CS1ArgLoc; if CS1 might Mod
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// CS1ArgLoc, then we care about either a Mod or a Ref by CS2. If CS1
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// might Ref, then we care only about a Mod by CS2.
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ModRefInfo ArgMask = getArgModRefInfo(CS1, CS1ArgIdx);
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ModRefInfo ArgR = getModRefInfo(CS2, CS1ArgLoc);
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if (((ArgMask & MRI_Mod) != MRI_NoModRef &&
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(ArgR & MRI_ModRef) != MRI_NoModRef) ||
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((ArgMask & MRI_Ref) != MRI_NoModRef &&
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(ArgR & MRI_Mod) != MRI_NoModRef))
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R = ModRefInfo((R | ArgMask) & Mask);
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if (R == Mask)
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break;
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}
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}
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return R;
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}
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// If this is the end of the chain, 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 ModRefInfo(AA->getModRefInfo(CS1, CS2) & Mask);
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}
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FunctionModRefBehavior AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
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assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
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auto Min = FMRB_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 the end of the chain, 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 FunctionModRefBehavior(AA->getModRefBehavior(CS) & Min);
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}
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FunctionModRefBehavior 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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//===----------------------------------------------------------------------===//
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// AliasAnalysis non-virtual helper method implementation
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//===----------------------------------------------------------------------===//
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ModRefInfo AliasAnalysis::getModRefInfo(const LoadInst *L,
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const MemoryLocation &Loc) {
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// Be conservative in the face of volatile/atomic.
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if (!L->isUnordered())
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return MRI_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 (Loc.Ptr && !alias(MemoryLocation::get(L), Loc))
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return MRI_NoModRef;
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// Otherwise, a load just reads.
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return MRI_Ref;
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}
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ModRefInfo AliasAnalysis::getModRefInfo(const StoreInst *S,
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const MemoryLocation &Loc) {
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// Be conservative in the face of volatile/atomic.
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if (!S->isUnordered())
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return MRI_ModRef;
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if (Loc.Ptr) {
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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(MemoryLocation::get(S), Loc))
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return MRI_NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have
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// been modified by this store.
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if (pointsToConstantMemory(Loc))
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return MRI_NoModRef;
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}
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// Otherwise, a store just writes.
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return MRI_Mod;
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}
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ModRefInfo AliasAnalysis::getModRefInfo(const VAArgInst *V,
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const MemoryLocation &Loc) {
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if (Loc.Ptr) {
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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(MemoryLocation::get(V), Loc))
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return MRI_NoModRef;
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// If the pointer is a pointer to constant memory, then it could not have
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// been modified by this va_arg.
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if (pointsToConstantMemory(Loc))
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return MRI_NoModRef;
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}
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// Otherwise, a va_arg reads and writes.
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return MRI_ModRef;
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}
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ModRefInfo AliasAnalysis::getModRefInfo(const AtomicCmpXchgInst *CX,
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const MemoryLocation &Loc) {
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// Acquire/Release cmpxchg has properties that matter for arbitrary addresses.
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if (CX->getSuccessOrdering() > Monotonic)
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return MRI_ModRef;
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// If the cmpxchg address does not alias the location, it does not access it.
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if (Loc.Ptr && !alias(MemoryLocation::get(CX), Loc))
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return MRI_NoModRef;
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return MRI_ModRef;
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}
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ModRefInfo AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW,
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const MemoryLocation &Loc) {
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// Acquire/Release atomicrmw has properties that matter for arbitrary addresses.
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if (RMW->getOrdering() > Monotonic)
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return MRI_ModRef;
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// If the atomicrmw address does not alias the location, it does not access it.
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if (Loc.Ptr && !alias(MemoryLocation::get(RMW), Loc))
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return MRI_NoModRef;
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return MRI_ModRef;
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}
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/// \brief Return information about whether a particular call site modifies
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/// or reads the specified memory location \p MemLoc before instruction \p I
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/// in a BasicBlock. A ordered basic block \p OBB can be used to speed up
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/// instruction-ordering queries inside the BasicBlock containing \p I.
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/// FIXME: this is really just shoring-up a deficiency in alias analysis.
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/// BasicAA isn't willing to spend linear time determining whether an alloca
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/// was captured before or after this particular call, while we are. However,
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/// with a smarter AA in place, this test is just wasting compile time.
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ModRefInfo AliasAnalysis::callCapturesBefore(const Instruction *I,
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const MemoryLocation &MemLoc,
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DominatorTree *DT,
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OrderedBasicBlock *OBB) {
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if (!DT)
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return MRI_ModRef;
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const Value *Object = GetUnderlyingObject(MemLoc.Ptr, *DL);
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if (!isIdentifiedObject(Object) || isa<GlobalValue>(Object) ||
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isa<Constant>(Object))
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return MRI_ModRef;
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ImmutableCallSite CS(I);
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if (!CS.getInstruction() || CS.getInstruction() == Object)
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return MRI_ModRef;
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if (llvm::PointerMayBeCapturedBefore(Object, /* ReturnCaptures */ true,
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/* StoreCaptures */ true, I, DT,
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/* include Object */ true,
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/* OrderedBasicBlock */ OBB))
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return MRI_ModRef;
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unsigned ArgNo = 0;
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ModRefInfo R = MRI_NoModRef;
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for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
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CI != CE; ++CI, ++ArgNo) {
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// Only look at the no-capture or byval pointer arguments. If this
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// pointer were passed to arguments that were neither of these, then it
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// couldn't be no-capture.
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if (!(*CI)->getType()->isPointerTy() ||
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(!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
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continue;
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// If this is a no-capture pointer argument, see if we can tell that it
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// is impossible to alias the pointer we're checking. If not, we have to
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// assume that the call could touch the pointer, even though it doesn't
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// escape.
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if (isNoAlias(MemoryLocation(*CI), MemoryLocation(Object)))
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continue;
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if (CS.doesNotAccessMemory(ArgNo))
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continue;
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if (CS.onlyReadsMemory(ArgNo)) {
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R = MRI_Ref;
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continue;
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}
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return MRI_ModRef;
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}
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return R;
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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, const DataLayout *NewDL) {
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DL = NewDL;
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auto *TLIP = P->getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
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TLI = TLIP ? &TLIP->getTLI() : nullptr;
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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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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the location Loc.
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///
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bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
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const MemoryLocation &Loc) {
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return canInstructionRangeModRef(BB.front(), BB.back(), Loc, MRI_Mod);
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}
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/// canInstructionRangeModRef - Return true if it is possible for the
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/// execution of the specified instructions to mod\ref (according to the
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/// mode) the location Loc. The instructions to consider are all
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/// of the instructions in the range of [I1,I2] INCLUSIVE.
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/// I1 and I2 must be in the same basic block.
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bool AliasAnalysis::canInstructionRangeModRef(const Instruction &I1,
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const Instruction &I2,
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const MemoryLocation &Loc,
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const ModRefInfo Mode) {
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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, Loc) & Mode)
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return true;
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return false;
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}
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/// isNoAliasCall - Return true if this pointer is returned by a noalias
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/// function.
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bool llvm::isNoAliasCall(const Value *V) {
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if (auto CS = ImmutableCallSite(V))
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return CS.paramHasAttr(0, Attribute::NoAlias);
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return false;
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}
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/// isNoAliasArgument - Return true if this is an argument with the noalias
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/// attribute.
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bool llvm::isNoAliasArgument(const Value *V)
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{
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if (const Argument *A = dyn_cast<Argument>(V))
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return A->hasNoAliasAttr();
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return false;
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}
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/// isIdentifiedObject - Return true if this pointer refers to a distinct and
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/// identifiable object. This returns true for:
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/// Global Variables and Functions (but not Global Aliases)
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/// Allocas and Mallocs
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/// ByVal and NoAlias Arguments
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/// NoAlias returns
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///
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bool llvm::isIdentifiedObject(const Value *V) {
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if (isa<AllocaInst>(V))
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return true;
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if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
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return true;
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if (isNoAliasCall(V))
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return true;
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if (const Argument *A = dyn_cast<Argument>(V))
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return A->hasNoAliasAttr() || A->hasByValAttr();
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return false;
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}
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/// isIdentifiedFunctionLocal - Return true if V is umabigously identified
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/// at the function-level. Different IdentifiedFunctionLocals can't alias.
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/// Further, an IdentifiedFunctionLocal can not alias with any function
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/// arguments other than itself, which is not necessarily true for
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/// IdentifiedObjects.
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bool llvm::isIdentifiedFunctionLocal(const Value *V)
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{
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return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
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}
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