DirectXShaderCompiler/lib/Analysis/AliasAnalysis.cpp

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//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the generic AliasAnalysis interface which is used as the
// common interface used by all clients and implementations of alias analysis.
//
// This file also implements the default version of the AliasAnalysis interface
// that is to be used when no other implementation is specified. This does some
// simple tests that detect obvious cases: two different global pointers cannot
// alias, a global cannot alias a malloc, two different mallocs cannot alias,
// etc.
//
// This alias analysis implementation really isn't very good for anything, but
// it is very fast, and makes a nice clean default implementation. Because it
// handles lots of little corner cases, other, more complex, alias analysis
// implementations may choose to rely on this pass to resolve these simple and
// easy cases.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CaptureTracking.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"
using namespace llvm;
// Register the AliasAnalysis interface, providing a nice name to refer to.
INITIALIZE_ANALYSIS_GROUP(AliasAnalysis, "Alias Analysis", NoAA)
char AliasAnalysis::ID = 0;
//===----------------------------------------------------------------------===//
// Default chaining methods
//===----------------------------------------------------------------------===//
AliasResult AliasAnalysis::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->alias(LocA, LocB);
}
bool AliasAnalysis::pointsToConstantMemory(const MemoryLocation &Loc,
bool OrLocal) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->pointsToConstantMemory(Loc, OrLocal);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getArgModRefInfo(ImmutableCallSite CS, unsigned ArgIdx) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->getArgModRefInfo(CS, ArgIdx);
}
void AliasAnalysis::deleteValue(Value *V) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->deleteValue(V);
}
void AliasAnalysis::addEscapingUse(Use &U) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->addEscapingUse(U);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(Instruction *I, ImmutableCallSite Call) {
// We may have two calls
if (auto CS = ImmutableCallSite(I)) {
// Check if the two calls modify the same memory
return getModRefInfo(Call, CS);
} else {
// Otherwise, check if the call modifies or references the
// location this memory access defines. The best we can say
// is that if the call references what this instruction
// defines, it must be clobbered by this location.
const MemoryLocation DefLoc = MemoryLocation::get(I);
if (getModRefInfo(Call, DefLoc) != AliasAnalysis::NoModRef)
return AliasAnalysis::ModRef;
}
return AliasAnalysis::NoModRef;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(ImmutableCallSite CS, const MemoryLocation &Loc) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
ModRefBehavior MRB = getModRefBehavior(CS);
if (MRB == DoesNotAccessMemory)
return NoModRef;
ModRefResult Mask = ModRef;
if (onlyReadsMemory(MRB))
Mask = Ref;
if (onlyAccessesArgPointees(MRB)) {
bool doesAlias = false;
ModRefResult AllArgsMask = NoModRef;
if (doesAccessArgPointees(MRB)) {
for (ImmutableCallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
AI != AE; ++AI) {
const Value *Arg = *AI;
if (!Arg->getType()->isPointerTy())
continue;
unsigned ArgIdx = std::distance(CS.arg_begin(), AI);
MemoryLocation ArgLoc =
MemoryLocation::getForArgument(CS, ArgIdx, *TLI);
if (!isNoAlias(ArgLoc, Loc)) {
ModRefResult ArgMask = getArgModRefInfo(CS, ArgIdx);
doesAlias = true;
AllArgsMask = ModRefResult(AllArgsMask | ArgMask);
}
}
}
if (!doesAlias)
return NoModRef;
Mask = ModRefResult(Mask & AllArgsMask);
}
// If Loc is a constant memory location, the call definitely could not
// modify the memory location.
if ((Mask & Mod) && pointsToConstantMemory(Loc))
Mask = ModRefResult(Mask & ~Mod);
// If this is the end of the chain, don't forward.
if (!AA) return Mask;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any mask we've managed to compute.
return ModRefResult(AA->getModRefInfo(CS, Loc) & Mask);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
// If CS1 or CS2 are readnone, they don't interact.
ModRefBehavior CS1B = getModRefBehavior(CS1);
if (CS1B == DoesNotAccessMemory) return NoModRef;
ModRefBehavior CS2B = getModRefBehavior(CS2);
if (CS2B == DoesNotAccessMemory) return NoModRef;
// If they both only read from memory, there is no dependence.
if (onlyReadsMemory(CS1B) && onlyReadsMemory(CS2B))
return NoModRef;
AliasAnalysis::ModRefResult Mask = ModRef;
// If CS1 only reads memory, the only dependence on CS2 can be
// from CS1 reading memory written by CS2.
if (onlyReadsMemory(CS1B))
Mask = ModRefResult(Mask & Ref);
// If CS2 only access memory through arguments, accumulate the mod/ref
// information from CS1's references to the memory referenced by
// CS2's arguments.
if (onlyAccessesArgPointees(CS2B)) {
AliasAnalysis::ModRefResult R = NoModRef;
if (doesAccessArgPointees(CS2B)) {
for (ImmutableCallSite::arg_iterator
I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
const Value *Arg = *I;
if (!Arg->getType()->isPointerTy())
continue;
unsigned CS2ArgIdx = std::distance(CS2.arg_begin(), I);
auto CS2ArgLoc = MemoryLocation::getForArgument(CS2, CS2ArgIdx, *TLI);
// ArgMask indicates what CS2 might do to CS2ArgLoc, and the dependence of
// CS1 on that location is the inverse.
ModRefResult ArgMask = getArgModRefInfo(CS2, CS2ArgIdx);
if (ArgMask == Mod)
ArgMask = ModRef;
else if (ArgMask == Ref)
ArgMask = Mod;
R = ModRefResult((R | (getModRefInfo(CS1, CS2ArgLoc) & ArgMask)) & Mask);
if (R == Mask)
break;
}
}
return R;
}
// If CS1 only accesses memory through arguments, check if CS2 references
// any of the memory referenced by CS1's arguments. If not, return NoModRef.
if (onlyAccessesArgPointees(CS1B)) {
AliasAnalysis::ModRefResult R = NoModRef;
if (doesAccessArgPointees(CS1B)) {
for (ImmutableCallSite::arg_iterator
I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I) {
const Value *Arg = *I;
if (!Arg->getType()->isPointerTy())
continue;
unsigned CS1ArgIdx = std::distance(CS1.arg_begin(), I);
auto CS1ArgLoc = MemoryLocation::getForArgument(CS1, CS1ArgIdx, *TLI);
// ArgMask indicates what CS1 might do to CS1ArgLoc; if CS1 might Mod
// CS1ArgLoc, then we care about either a Mod or a Ref by CS2. If CS1
// might Ref, then we care only about a Mod by CS2.
ModRefResult ArgMask = getArgModRefInfo(CS1, CS1ArgIdx);
ModRefResult ArgR = getModRefInfo(CS2, CS1ArgLoc);
if (((ArgMask & Mod) != NoModRef && (ArgR & ModRef) != NoModRef) ||
((ArgMask & Ref) != NoModRef && (ArgR & Mod) != NoModRef))
R = ModRefResult((R | ArgMask) & Mask);
if (R == Mask)
break;
}
}
return R;
}
// If this is the end of the chain, don't forward.
if (!AA) return Mask;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any mask we've managed to compute.
return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask);
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
ModRefBehavior Min = UnknownModRefBehavior;
// Call back into the alias analysis with the other form of getModRefBehavior
// to see if it can give a better response.
if (const Function *F = CS.getCalledFunction())
Min = getModRefBehavior(F);
// If this is the end of the chain, don't forward.
if (!AA) return Min;
// Otherwise, fall back to the next AA in the chain. But we can merge
// in any result we've managed to compute.
return ModRefBehavior(AA->getModRefBehavior(CS) & Min);
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(const Function *F) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->getModRefBehavior(F);
}
//===----------------------------------------------------------------------===//
// AliasAnalysis non-virtual helper method implementation
//===----------------------------------------------------------------------===//
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const LoadInst *L, const MemoryLocation &Loc) {
// Be conservative in the face of volatile/atomic.
if (!L->isUnordered())
return ModRef;
// If the load address doesn't alias the given address, it doesn't read
// or write the specified memory.
if (Loc.Ptr && !alias(MemoryLocation::get(L), Loc))
return NoModRef;
// Otherwise, a load just reads.
return Ref;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const StoreInst *S, const MemoryLocation &Loc) {
// Be conservative in the face of volatile/atomic.
if (!S->isUnordered())
return ModRef;
if (Loc.Ptr) {
// If the store address cannot alias the pointer in question, then the
// specified memory cannot be modified by the store.
if (!alias(MemoryLocation::get(S), Loc))
return NoModRef;
// If the pointer is a pointer to constant memory, then it could not have
// been modified by this store.
if (pointsToConstantMemory(Loc))
return NoModRef;
}
// Otherwise, a store just writes.
return Mod;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const VAArgInst *V, const MemoryLocation &Loc) {
if (Loc.Ptr) {
// If the va_arg address cannot alias the pointer in question, then the
// specified memory cannot be accessed by the va_arg.
if (!alias(MemoryLocation::get(V), Loc))
return NoModRef;
// If the pointer is a pointer to constant memory, then it could not have
// been modified by this va_arg.
if (pointsToConstantMemory(Loc))
return NoModRef;
}
// Otherwise, a va_arg reads and writes.
return ModRef;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const AtomicCmpXchgInst *CX,
const MemoryLocation &Loc) {
// Acquire/Release cmpxchg has properties that matter for arbitrary addresses.
if (CX->getSuccessOrdering() > Monotonic)
return ModRef;
// If the cmpxchg address does not alias the location, it does not access it.
if (Loc.Ptr && !alias(MemoryLocation::get(CX), Loc))
return NoModRef;
return ModRef;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW,
const MemoryLocation &Loc) {
// Acquire/Release atomicrmw has properties that matter for arbitrary addresses.
if (RMW->getOrdering() > Monotonic)
return ModRef;
// If the atomicrmw address does not alias the location, it does not access it.
if (Loc.Ptr && !alias(MemoryLocation::get(RMW), Loc))
return NoModRef;
return ModRef;
}
// FIXME: this is really just shoring-up a deficiency in alias analysis.
// BasicAA isn't willing to spend linear time determining whether an alloca
// was captured before or after this particular call, while we are. However,
// with a smarter AA in place, this test is just wasting compile time.
AliasAnalysis::ModRefResult AliasAnalysis::callCapturesBefore(
const Instruction *I, const MemoryLocation &MemLoc, DominatorTree *DT) {
if (!DT)
return AliasAnalysis::ModRef;
const Value *Object = GetUnderlyingObject(MemLoc.Ptr, *DL);
if (!isIdentifiedObject(Object) || isa<GlobalValue>(Object) ||
isa<Constant>(Object))
return AliasAnalysis::ModRef;
ImmutableCallSite CS(I);
if (!CS.getInstruction() || CS.getInstruction() == Object)
return AliasAnalysis::ModRef;
if (llvm::PointerMayBeCapturedBefore(Object, /* ReturnCaptures */ true,
/* StoreCaptures */ true, I, DT,
/* include Object */ true))
return AliasAnalysis::ModRef;
unsigned ArgNo = 0;
AliasAnalysis::ModRefResult R = AliasAnalysis::NoModRef;
for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
CI != CE; ++CI, ++ArgNo) {
// Only look at the no-capture or byval pointer arguments. If this
// pointer were passed to arguments that were neither of these, then it
// couldn't be no-capture.
if (!(*CI)->getType()->isPointerTy() ||
(!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
continue;
// If this is a no-capture pointer argument, see if we can tell that it
// is impossible to alias the pointer we're checking. If not, we have to
// assume that the call could touch the pointer, even though it doesn't
// escape.
if (isNoAlias(MemoryLocation(*CI), MemoryLocation(Object)))
continue;
if (CS.doesNotAccessMemory(ArgNo))
continue;
if (CS.onlyReadsMemory(ArgNo)) {
R = AliasAnalysis::Ref;
continue;
}
return AliasAnalysis::ModRef;
}
return R;
}
// AliasAnalysis destructor: DO NOT move this to the header file for
// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
// the AliasAnalysis.o file in the current .a file, causing alias analysis
// support to not be included in the tool correctly!
//
AliasAnalysis::~AliasAnalysis() {}
/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
/// AliasAnalysis interface before any other methods are called.
///
void AliasAnalysis::InitializeAliasAnalysis(Pass *P, const DataLayout *NewDL) {
DL = NewDL;
auto *TLIP = P->getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
TLI = TLIP ? &TLIP->getTLI() : nullptr;
AA = &P->getAnalysis<AliasAnalysis>();
}
// getAnalysisUsage - All alias analysis implementations should invoke this
// directly (using AliasAnalysis::getAnalysisUsage(AU)).
void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>(); // All AA's chain
}
/// getTypeStoreSize - Return the DataLayout store size for the given type,
/// if known, or a conservative value otherwise.
///
uint64_t AliasAnalysis::getTypeStoreSize(Type *Ty) {
return DL ? DL->getTypeStoreSize(Ty) : MemoryLocation::UnknownSize;
}
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the location Loc.
///
bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
const MemoryLocation &Loc) {
return canInstructionRangeModRef(BB.front(), BB.back(), Loc, Mod);
}
/// canInstructionRangeModRef - Return true if it is possible for the
/// execution of the specified instructions to mod\ref (according to the
/// mode) the location Loc. The instructions to consider are all
/// of the instructions in the range of [I1,I2] INCLUSIVE.
/// I1 and I2 must be in the same basic block.
bool AliasAnalysis::canInstructionRangeModRef(const Instruction &I1,
const Instruction &I2,
const MemoryLocation &Loc,
const ModRefResult Mode) {
assert(I1.getParent() == I2.getParent() &&
"Instructions not in same basic block!");
BasicBlock::const_iterator I = &I1;
BasicBlock::const_iterator E = &I2;
++E; // Convert from inclusive to exclusive range.
for (; I != E; ++I) // Check every instruction in range
if (getModRefInfo(I, Loc) & Mode)
return true;
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;
}
/// isNoAliasArgument - Return true if this is an argument with the noalias
/// attribute.
bool llvm::isNoAliasArgument(const Value *V)
{
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasNoAliasAttr();
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;
}
/// isIdentifiedFunctionLocal - Return true if V is umabigously identified
/// at the function-level. Different IdentifiedFunctionLocals can't alias.
/// Further, an IdentifiedFunctionLocal can not alias with any function
/// arguments other than itself, which is not necessarily true for
/// IdentifiedObjects.
bool llvm::isIdentifiedFunctionLocal(const Value *V)
{
return isa<AllocaInst>(V) || isNoAliasCall(V) || isNoAliasArgument(V);
}