mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-12-16 11:30:51 +00:00
f23c6af13d
We already had a method to iterate over all the incoming values of a PHI. This just changes all eligible code to use it. Ineligible code included anything which cared about the index, or was also trying to get the i'th incoming BB. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237169 91177308-0d34-0410-b5e6-96231b3b80d8
1734 lines
70 KiB
C++
1734 lines
70 KiB
C++
//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file defines the primary stateless implementation of the
|
|
// Alias Analysis interface that implements identities (two different
|
|
// globals cannot alias, etc), but does no stateful analysis.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Analysis/Passes.h"
|
|
#include "llvm/ADT/SmallPtrSet.h"
|
|
#include "llvm/ADT/SmallVector.h"
|
|
#include "llvm/Analysis/AliasAnalysis.h"
|
|
#include "llvm/Analysis/AssumptionCache.h"
|
|
#include "llvm/Analysis/CFG.h"
|
|
#include "llvm/Analysis/CaptureTracking.h"
|
|
#include "llvm/Analysis/InstructionSimplify.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
#include "llvm/Analysis/MemoryBuiltins.h"
|
|
#include "llvm/Analysis/TargetLibraryInfo.h"
|
|
#include "llvm/Analysis/ValueTracking.h"
|
|
#include "llvm/IR/Constants.h"
|
|
#include "llvm/IR/DataLayout.h"
|
|
#include "llvm/IR/DerivedTypes.h"
|
|
#include "llvm/IR/Dominators.h"
|
|
#include "llvm/IR/Function.h"
|
|
#include "llvm/IR/GetElementPtrTypeIterator.h"
|
|
#include "llvm/IR/GlobalAlias.h"
|
|
#include "llvm/IR/GlobalVariable.h"
|
|
#include "llvm/IR/Instructions.h"
|
|
#include "llvm/IR/IntrinsicInst.h"
|
|
#include "llvm/IR/LLVMContext.h"
|
|
#include "llvm/IR/Operator.h"
|
|
#include "llvm/Pass.h"
|
|
#include "llvm/Support/ErrorHandling.h"
|
|
#include <algorithm>
|
|
using namespace llvm;
|
|
|
|
/// Cutoff after which to stop analysing a set of phi nodes potentially involved
|
|
/// in a cycle. Because we are analysing 'through' phi nodes we need to be
|
|
/// careful with value equivalence. We use reachability to make sure a value
|
|
/// cannot be involved in a cycle.
|
|
const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
|
|
|
|
// The max limit of the search depth in DecomposeGEPExpression() and
|
|
// GetUnderlyingObject(), both functions need to use the same search
|
|
// depth otherwise the algorithm in aliasGEP will assert.
|
|
static const unsigned MaxLookupSearchDepth = 6;
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// Useful predicates
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
|
|
/// object that never escapes from the function.
|
|
static bool isNonEscapingLocalObject(const Value *V) {
|
|
// If this is a local allocation, check to see if it escapes.
|
|
if (isa<AllocaInst>(V) || isNoAliasCall(V))
|
|
// Set StoreCaptures to True so that we can assume in our callers that the
|
|
// pointer is not the result of a load instruction. Currently
|
|
// PointerMayBeCaptured doesn't have any special analysis for the
|
|
// StoreCaptures=false case; if it did, our callers could be refined to be
|
|
// more precise.
|
|
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
|
|
|
|
// If this is an argument that corresponds to a byval or noalias argument,
|
|
// then it has not escaped before entering the function. Check if it escapes
|
|
// inside the function.
|
|
if (const Argument *A = dyn_cast<Argument>(V))
|
|
if (A->hasByValAttr() || A->hasNoAliasAttr())
|
|
// Note even if the argument is marked nocapture we still need to check
|
|
// for copies made inside the function. The nocapture attribute only
|
|
// specifies that there are no copies made that outlive the function.
|
|
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
|
|
|
|
return false;
|
|
}
|
|
|
|
/// isEscapeSource - Return true if the pointer is one which would have
|
|
/// been considered an escape by isNonEscapingLocalObject.
|
|
static bool isEscapeSource(const Value *V) {
|
|
if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
|
|
return true;
|
|
|
|
// The load case works because isNonEscapingLocalObject considers all
|
|
// stores to be escapes (it passes true for the StoreCaptures argument
|
|
// to PointerMayBeCaptured).
|
|
if (isa<LoadInst>(V))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// getObjectSize - Return the size of the object specified by V, or
|
|
/// UnknownSize if unknown.
|
|
static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
|
|
const TargetLibraryInfo &TLI,
|
|
bool RoundToAlign = false) {
|
|
uint64_t Size;
|
|
if (getObjectSize(V, Size, DL, &TLI, RoundToAlign))
|
|
return Size;
|
|
return AliasAnalysis::UnknownSize;
|
|
}
|
|
|
|
/// isObjectSmallerThan - Return true if we can prove that the object specified
|
|
/// by V is smaller than Size.
|
|
static bool isObjectSmallerThan(const Value *V, uint64_t Size,
|
|
const DataLayout &DL,
|
|
const TargetLibraryInfo &TLI) {
|
|
// Note that the meanings of the "object" are slightly different in the
|
|
// following contexts:
|
|
// c1: llvm::getObjectSize()
|
|
// c2: llvm.objectsize() intrinsic
|
|
// c3: isObjectSmallerThan()
|
|
// c1 and c2 share the same meaning; however, the meaning of "object" in c3
|
|
// refers to the "entire object".
|
|
//
|
|
// Consider this example:
|
|
// char *p = (char*)malloc(100)
|
|
// char *q = p+80;
|
|
//
|
|
// In the context of c1 and c2, the "object" pointed by q refers to the
|
|
// stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
|
|
//
|
|
// However, in the context of c3, the "object" refers to the chunk of memory
|
|
// being allocated. So, the "object" has 100 bytes, and q points to the middle
|
|
// the "object". In case q is passed to isObjectSmallerThan() as the 1st
|
|
// parameter, before the llvm::getObjectSize() is called to get the size of
|
|
// entire object, we should:
|
|
// - either rewind the pointer q to the base-address of the object in
|
|
// question (in this case rewind to p), or
|
|
// - just give up. It is up to caller to make sure the pointer is pointing
|
|
// to the base address the object.
|
|
//
|
|
// We go for 2nd option for simplicity.
|
|
if (!isIdentifiedObject(V))
|
|
return false;
|
|
|
|
// This function needs to use the aligned object size because we allow
|
|
// reads a bit past the end given sufficient alignment.
|
|
uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/true);
|
|
|
|
return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
|
|
}
|
|
|
|
/// isObjectSize - Return true if we can prove that the object specified
|
|
/// by V has size Size.
|
|
static bool isObjectSize(const Value *V, uint64_t Size,
|
|
const DataLayout &DL, const TargetLibraryInfo &TLI) {
|
|
uint64_t ObjectSize = getObjectSize(V, DL, TLI);
|
|
return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// GetElementPtr Instruction Decomposition and Analysis
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
namespace {
|
|
|
|
// A linear transformation of a Value; this class represents ZExt(SExt(V,
|
|
// SExtBits), ZExtBits) * Scale + Offset.
|
|
struct VariableGEPIndex {
|
|
|
|
// An opaque Value - we can't decompose this further.
|
|
const Value *V;
|
|
|
|
// We need to track what extensions we've done as we consider the same Value
|
|
// with different extensions as different variables in a GEP's linear
|
|
// expression;
|
|
// e.g.: if V == -1, then sext(x) != zext(x).
|
|
unsigned ZExtBits;
|
|
unsigned SExtBits;
|
|
|
|
int64_t Scale;
|
|
|
|
bool operator==(const VariableGEPIndex &Other) const {
|
|
return V == Other.V && ZExtBits == Other.ZExtBits &&
|
|
SExtBits == Other.SExtBits && Scale == Other.Scale;
|
|
}
|
|
|
|
bool operator!=(const VariableGEPIndex &Other) const {
|
|
return !operator==(Other);
|
|
}
|
|
};
|
|
}
|
|
|
|
|
|
/// GetLinearExpression - Analyze the specified value as a linear expression:
|
|
/// "A*V + B", where A and B are constant integers. Return the scale and offset
|
|
/// values as APInts and return V as a Value*, and return whether we looked
|
|
/// through any sign or zero extends. The incoming Value is known to have
|
|
/// IntegerType and it may already be sign or zero extended.
|
|
///
|
|
/// Note that this looks through extends, so the high bits may not be
|
|
/// represented in the result.
|
|
static const Value *GetLinearExpression(const Value *V, APInt &Scale,
|
|
APInt &Offset, unsigned &ZExtBits,
|
|
unsigned &SExtBits,
|
|
const DataLayout &DL, unsigned Depth,
|
|
AssumptionCache *AC, DominatorTree *DT,
|
|
bool &NSW, bool &NUW) {
|
|
assert(V->getType()->isIntegerTy() && "Not an integer value");
|
|
|
|
// Limit our recursion depth.
|
|
if (Depth == 6) {
|
|
Scale = 1;
|
|
Offset = 0;
|
|
return V;
|
|
}
|
|
|
|
if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
|
|
// if it's a constant, just convert it to an offset and remove the variable.
|
|
// If we've been called recursively the Offset bit width will be greater
|
|
// than the constant's (the Offset's always as wide as the outermost call),
|
|
// so we'll zext here and process any extension in the isa<SExtInst> &
|
|
// isa<ZExtInst> cases below.
|
|
Offset += Const->getValue().zextOrSelf(Offset.getBitWidth());
|
|
assert(Scale == 0 && "Constant values don't have a scale");
|
|
return V;
|
|
}
|
|
|
|
if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
|
|
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
|
|
|
|
// If we've been called recursively then Offset and Scale will be wider
|
|
// that the BOp operands. We'll always zext it here as we'll process sign
|
|
// extensions below (see the isa<SExtInst> / isa<ZExtInst> cases).
|
|
APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth());
|
|
|
|
switch (BOp->getOpcode()) {
|
|
default:
|
|
// We don't understand this instruction, so we can't decompose it any
|
|
// further.
|
|
Scale = 1;
|
|
Offset = 0;
|
|
return V;
|
|
case Instruction::Or:
|
|
// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
|
|
// analyze it.
|
|
if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC,
|
|
BOp, DT))
|
|
break;
|
|
// FALL THROUGH.
|
|
case Instruction::Add:
|
|
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
|
|
SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
|
|
Offset += RHS;
|
|
break;
|
|
case Instruction::Sub:
|
|
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
|
|
SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
|
|
Offset -= RHS;
|
|
break;
|
|
case Instruction::Mul:
|
|
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
|
|
SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
|
|
Offset *= RHS;
|
|
Scale *= RHS;
|
|
break;
|
|
case Instruction::Shl:
|
|
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
|
|
SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
|
|
Offset <<= RHS.getLimitedValue();
|
|
Scale <<= RHS.getLimitedValue();
|
|
// the semantics of nsw and nuw for left shifts don't match those of
|
|
// multiplications, so we won't propagate them.
|
|
NSW = NUW = false;
|
|
return V;
|
|
}
|
|
|
|
if (isa<OverflowingBinaryOperator>(BOp)) {
|
|
NUW &= BOp->hasNoUnsignedWrap();
|
|
NSW &= BOp->hasNoSignedWrap();
|
|
}
|
|
return V;
|
|
}
|
|
}
|
|
|
|
// Since GEP indices are sign extended anyway, we don't care about the high
|
|
// bits of a sign or zero extended value - just scales and offsets. The
|
|
// extensions have to be consistent though.
|
|
if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
|
|
Value *CastOp = cast<CastInst>(V)->getOperand(0);
|
|
unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
|
|
unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
|
|
unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits;
|
|
const Value *Result =
|
|
GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL,
|
|
Depth + 1, AC, DT, NSW, NUW);
|
|
|
|
// zext(zext(%x)) == zext(%x), and similiarly for sext; we'll handle this
|
|
// by just incrementing the number of bits we've extended by.
|
|
unsigned ExtendedBy = NewWidth - SmallWidth;
|
|
|
|
if (isa<SExtInst>(V) && ZExtBits == 0) {
|
|
// sext(sext(%x, a), b) == sext(%x, a + b)
|
|
|
|
if (NSW) {
|
|
// We haven't sign-wrapped, so it's valid to decompose sext(%x + c)
|
|
// into sext(%x) + sext(c). We'll sext the Offset ourselves:
|
|
unsigned OldWidth = Offset.getBitWidth();
|
|
Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth);
|
|
} else {
|
|
// We may have signed-wrapped, so don't decompose sext(%x + c) into
|
|
// sext(%x) + sext(c)
|
|
Scale = 1;
|
|
Offset = 0;
|
|
Result = CastOp;
|
|
ZExtBits = OldZExtBits;
|
|
SExtBits = OldSExtBits;
|
|
}
|
|
SExtBits += ExtendedBy;
|
|
} else {
|
|
// sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b)
|
|
|
|
if (!NUW) {
|
|
// We may have unsigned-wrapped, so don't decompose zext(%x + c) into
|
|
// zext(%x) + zext(c)
|
|
Scale = 1;
|
|
Offset = 0;
|
|
Result = CastOp;
|
|
ZExtBits = OldZExtBits;
|
|
SExtBits = OldSExtBits;
|
|
}
|
|
ZExtBits += ExtendedBy;
|
|
}
|
|
|
|
return Result;
|
|
}
|
|
|
|
Scale = 1;
|
|
Offset = 0;
|
|
return V;
|
|
}
|
|
|
|
/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
|
|
/// into a base pointer with a constant offset and a number of scaled symbolic
|
|
/// offsets.
|
|
///
|
|
/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
|
|
/// the VarIndices vector) are Value*'s that are known to be scaled by the
|
|
/// specified amount, but which may have other unrepresented high bits. As such,
|
|
/// the gep cannot necessarily be reconstructed from its decomposed form.
|
|
///
|
|
/// When DataLayout is around, this function is capable of analyzing everything
|
|
/// that GetUnderlyingObject can look through. To be able to do that
|
|
/// GetUnderlyingObject and DecomposeGEPExpression must use the same search
|
|
/// depth (MaxLookupSearchDepth).
|
|
/// When DataLayout not is around, it just looks through pointer casts.
|
|
///
|
|
static const Value *
|
|
DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
|
|
SmallVectorImpl<VariableGEPIndex> &VarIndices,
|
|
bool &MaxLookupReached, const DataLayout &DL,
|
|
AssumptionCache *AC, DominatorTree *DT) {
|
|
// Limit recursion depth to limit compile time in crazy cases.
|
|
unsigned MaxLookup = MaxLookupSearchDepth;
|
|
MaxLookupReached = false;
|
|
|
|
BaseOffs = 0;
|
|
do {
|
|
// See if this is a bitcast or GEP.
|
|
const Operator *Op = dyn_cast<Operator>(V);
|
|
if (!Op) {
|
|
// The only non-operator case we can handle are GlobalAliases.
|
|
if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
|
|
if (!GA->mayBeOverridden()) {
|
|
V = GA->getAliasee();
|
|
continue;
|
|
}
|
|
}
|
|
return V;
|
|
}
|
|
|
|
if (Op->getOpcode() == Instruction::BitCast ||
|
|
Op->getOpcode() == Instruction::AddrSpaceCast) {
|
|
V = Op->getOperand(0);
|
|
continue;
|
|
}
|
|
|
|
const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
|
|
if (!GEPOp) {
|
|
// If it's not a GEP, hand it off to SimplifyInstruction to see if it
|
|
// can come up with something. This matches what GetUnderlyingObject does.
|
|
if (const Instruction *I = dyn_cast<Instruction>(V))
|
|
// TODO: Get a DominatorTree and AssumptionCache and use them here
|
|
// (these are both now available in this function, but this should be
|
|
// updated when GetUnderlyingObject is updated). TLI should be
|
|
// provided also.
|
|
if (const Value *Simplified =
|
|
SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
|
|
V = Simplified;
|
|
continue;
|
|
}
|
|
|
|
return V;
|
|
}
|
|
|
|
// Don't attempt to analyze GEPs over unsized objects.
|
|
if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
|
|
return V;
|
|
|
|
unsigned AS = GEPOp->getPointerAddressSpace();
|
|
// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
|
|
gep_type_iterator GTI = gep_type_begin(GEPOp);
|
|
for (User::const_op_iterator I = GEPOp->op_begin()+1,
|
|
E = GEPOp->op_end(); I != E; ++I) {
|
|
const Value *Index = *I;
|
|
// Compute the (potentially symbolic) offset in bytes for this index.
|
|
if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
|
|
// For a struct, add the member offset.
|
|
unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
|
|
if (FieldNo == 0) continue;
|
|
|
|
BaseOffs += DL.getStructLayout(STy)->getElementOffset(FieldNo);
|
|
continue;
|
|
}
|
|
|
|
// For an array/pointer, add the element offset, explicitly scaled.
|
|
if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
|
|
if (CIdx->isZero()) continue;
|
|
BaseOffs += DL.getTypeAllocSize(*GTI) * CIdx->getSExtValue();
|
|
continue;
|
|
}
|
|
|
|
uint64_t Scale = DL.getTypeAllocSize(*GTI);
|
|
unsigned ZExtBits = 0, SExtBits = 0;
|
|
|
|
// If the integer type is smaller than the pointer size, it is implicitly
|
|
// sign extended to pointer size.
|
|
unsigned Width = Index->getType()->getIntegerBitWidth();
|
|
unsigned PointerSize = DL.getPointerSizeInBits(AS);
|
|
if (PointerSize > Width)
|
|
SExtBits += PointerSize - Width;
|
|
|
|
// Use GetLinearExpression to decompose the index into a C1*V+C2 form.
|
|
APInt IndexScale(Width, 0), IndexOffset(Width, 0);
|
|
bool NSW = true, NUW = true;
|
|
Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits,
|
|
SExtBits, DL, 0, AC, DT, NSW, NUW);
|
|
|
|
// The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
|
|
// This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
|
|
BaseOffs += IndexOffset.getSExtValue()*Scale;
|
|
Scale *= IndexScale.getSExtValue();
|
|
|
|
// If we already had an occurrence of this index variable, merge this
|
|
// scale into it. For example, we want to handle:
|
|
// A[x][x] -> x*16 + x*4 -> x*20
|
|
// This also ensures that 'x' only appears in the index list once.
|
|
for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
|
|
if (VarIndices[i].V == Index && VarIndices[i].ZExtBits == ZExtBits &&
|
|
VarIndices[i].SExtBits == SExtBits) {
|
|
Scale += VarIndices[i].Scale;
|
|
VarIndices.erase(VarIndices.begin()+i);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Make sure that we have a scale that makes sense for this target's
|
|
// pointer size.
|
|
if (unsigned ShiftBits = 64 - PointerSize) {
|
|
Scale <<= ShiftBits;
|
|
Scale = (int64_t)Scale >> ShiftBits;
|
|
}
|
|
|
|
if (Scale) {
|
|
VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
|
|
static_cast<int64_t>(Scale)};
|
|
VarIndices.push_back(Entry);
|
|
}
|
|
}
|
|
|
|
// Analyze the base pointer next.
|
|
V = GEPOp->getOperand(0);
|
|
} while (--MaxLookup);
|
|
|
|
// If the chain of expressions is too deep, just return early.
|
|
MaxLookupReached = true;
|
|
return V;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// BasicAliasAnalysis Pass
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef NDEBUG
|
|
static const Function *getParent(const Value *V) {
|
|
if (const Instruction *inst = dyn_cast<Instruction>(V))
|
|
return inst->getParent()->getParent();
|
|
|
|
if (const Argument *arg = dyn_cast<Argument>(V))
|
|
return arg->getParent();
|
|
|
|
return nullptr;
|
|
}
|
|
|
|
static bool notDifferentParent(const Value *O1, const Value *O2) {
|
|
|
|
const Function *F1 = getParent(O1);
|
|
const Function *F2 = getParent(O2);
|
|
|
|
return !F1 || !F2 || F1 == F2;
|
|
}
|
|
#endif
|
|
|
|
namespace {
|
|
/// BasicAliasAnalysis - This is the primary alias analysis implementation.
|
|
struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
|
|
static char ID; // Class identification, replacement for typeinfo
|
|
BasicAliasAnalysis() : ImmutablePass(ID) {
|
|
initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool doInitialization(Module &M) override;
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<AliasAnalysis>();
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
}
|
|
|
|
AliasResult alias(const Location &LocA, const Location &LocB) override {
|
|
assert(AliasCache.empty() && "AliasCache must be cleared after use!");
|
|
assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
|
|
"BasicAliasAnalysis doesn't support interprocedural queries.");
|
|
AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags,
|
|
LocB.Ptr, LocB.Size, LocB.AATags);
|
|
// AliasCache rarely has more than 1 or 2 elements, always use
|
|
// shrink_and_clear so it quickly returns to the inline capacity of the
|
|
// SmallDenseMap if it ever grows larger.
|
|
// FIXME: This should really be shrink_to_inline_capacity_and_clear().
|
|
AliasCache.shrink_and_clear();
|
|
VisitedPhiBBs.clear();
|
|
return Alias;
|
|
}
|
|
|
|
ModRefResult getModRefInfo(ImmutableCallSite CS,
|
|
const Location &Loc) override;
|
|
|
|
ModRefResult getModRefInfo(ImmutableCallSite CS1,
|
|
ImmutableCallSite CS2) override;
|
|
|
|
/// pointsToConstantMemory - Chase pointers until we find a (constant
|
|
/// global) or not.
|
|
bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override;
|
|
|
|
/// Get the location associated with a pointer argument of a callsite.
|
|
Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
|
|
ModRefResult &Mask) override;
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given
|
|
/// call site.
|
|
ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given function.
|
|
/// For use when the call site is not known.
|
|
ModRefBehavior getModRefBehavior(const Function *F) override;
|
|
|
|
/// getAdjustedAnalysisPointer - This method is used when a pass implements
|
|
/// an analysis interface through multiple inheritance. If needed, it
|
|
/// should override this to adjust the this pointer as needed for the
|
|
/// specified pass info.
|
|
void *getAdjustedAnalysisPointer(const void *ID) override {
|
|
if (ID == &AliasAnalysis::ID)
|
|
return (AliasAnalysis*)this;
|
|
return this;
|
|
}
|
|
|
|
private:
|
|
// AliasCache - Track alias queries to guard against recursion.
|
|
typedef std::pair<Location, Location> LocPair;
|
|
typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
|
|
AliasCacheTy AliasCache;
|
|
|
|
/// \brief Track phi nodes we have visited. When interpret "Value" pointer
|
|
/// equality as value equality we need to make sure that the "Value" is not
|
|
/// part of a cycle. Otherwise, two uses could come from different
|
|
/// "iterations" of a cycle and see different values for the same "Value"
|
|
/// pointer.
|
|
/// The following example shows the problem:
|
|
/// %p = phi(%alloca1, %addr2)
|
|
/// %l = load %ptr
|
|
/// %addr1 = gep, %alloca2, 0, %l
|
|
/// %addr2 = gep %alloca2, 0, (%l + 1)
|
|
/// alias(%p, %addr1) -> MayAlias !
|
|
/// store %l, ...
|
|
SmallPtrSet<const BasicBlock*, 8> VisitedPhiBBs;
|
|
|
|
// Visited - Track instructions visited by pointsToConstantMemory.
|
|
SmallPtrSet<const Value*, 16> Visited;
|
|
|
|
/// \brief Check whether two Values can be considered equivalent.
|
|
///
|
|
/// In addition to pointer equivalence of \p V1 and \p V2 this checks
|
|
/// whether they can not be part of a cycle in the value graph by looking at
|
|
/// all visited phi nodes an making sure that the phis cannot reach the
|
|
/// value. We have to do this because we are looking through phi nodes (That
|
|
/// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
|
|
bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
|
|
|
|
/// \brief A Heuristic for aliasGEP that searches for a constant offset
|
|
/// between the variables.
|
|
///
|
|
/// GetLinearExpression has some limitations, as generally zext(%x + 1)
|
|
/// != zext(%x) + zext(1) if the arithmetic overflows. GetLinearExpression
|
|
/// will therefore conservatively refuse to decompose these expressions.
|
|
/// However, we know that, for all %x, zext(%x) != zext(%x + 1), even if
|
|
/// the addition overflows.
|
|
bool
|
|
constantOffsetHeuristic(const SmallVectorImpl<VariableGEPIndex> &VarIndices,
|
|
uint64_t V1Size, uint64_t V2Size,
|
|
int64_t BaseOffset, const DataLayout *DL,
|
|
AssumptionCache *AC, DominatorTree *DT);
|
|
|
|
/// \brief Dest and Src are the variable indices from two decomposed
|
|
/// GetElementPtr instructions GEP1 and GEP2 which have common base
|
|
/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
|
|
/// difference between the two pointers.
|
|
void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
|
|
const SmallVectorImpl<VariableGEPIndex> &Src);
|
|
|
|
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
|
|
// instruction against another.
|
|
AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
|
|
const AAMDNodes &V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo,
|
|
const Value *UnderlyingV1, const Value *UnderlyingV2);
|
|
|
|
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
|
|
// instruction against another.
|
|
AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const AAMDNodes &PNAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo);
|
|
|
|
/// aliasSelect - Disambiguate a Select instruction against another value.
|
|
AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const AAMDNodes &SIAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo);
|
|
|
|
AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
|
|
AAMDNodes V1AATag,
|
|
const Value *V2, uint64_t V2Size,
|
|
AAMDNodes V2AATag);
|
|
};
|
|
} // End of anonymous namespace
|
|
|
|
// Register this pass...
|
|
char BasicAliasAnalysis::ID = 0;
|
|
INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)",
|
|
false, true, false)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)",
|
|
false, true, false)
|
|
|
|
|
|
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
|
|
return new BasicAliasAnalysis();
|
|
}
|
|
|
|
/// pointsToConstantMemory - Returns whether the given pointer value
|
|
/// points to memory that is local to the function, with global constants being
|
|
/// considered local to all functions.
|
|
bool
|
|
BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
|
|
assert(Visited.empty() && "Visited must be cleared after use!");
|
|
|
|
unsigned MaxLookup = 8;
|
|
SmallVector<const Value *, 16> Worklist;
|
|
Worklist.push_back(Loc.Ptr);
|
|
do {
|
|
const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), *DL);
|
|
if (!Visited.insert(V).second) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
|
|
// An alloca instruction defines local memory.
|
|
if (OrLocal && isa<AllocaInst>(V))
|
|
continue;
|
|
|
|
// A global constant counts as local memory for our purposes.
|
|
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
|
|
// Note: this doesn't require GV to be "ODR" because it isn't legal for a
|
|
// global to be marked constant in some modules and non-constant in
|
|
// others. GV may even be a declaration, not a definition.
|
|
if (!GV->isConstant()) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
// If both select values point to local memory, then so does the select.
|
|
if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
|
|
Worklist.push_back(SI->getTrueValue());
|
|
Worklist.push_back(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
|
|
// If all values incoming to a phi node point to local memory, then so does
|
|
// the phi.
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
|
|
// Don't bother inspecting phi nodes with many operands.
|
|
if (PN->getNumIncomingValues() > MaxLookup) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
for (Value *IncValue : PN->incoming_values())
|
|
Worklist.push_back(IncValue);
|
|
continue;
|
|
}
|
|
|
|
// Otherwise be conservative.
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
|
|
} while (!Worklist.empty() && --MaxLookup);
|
|
|
|
Visited.clear();
|
|
return Worklist.empty();
|
|
}
|
|
|
|
static bool isMemsetPattern16(const Function *MS,
|
|
const TargetLibraryInfo &TLI) {
|
|
if (TLI.has(LibFunc::memset_pattern16) &&
|
|
MS->getName() == "memset_pattern16") {
|
|
FunctionType *MemsetType = MS->getFunctionType();
|
|
if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
|
|
isa<PointerType>(MemsetType->getParamType(0)) &&
|
|
isa<PointerType>(MemsetType->getParamType(1)) &&
|
|
isa<IntegerType>(MemsetType->getParamType(2)))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given call site.
|
|
AliasAnalysis::ModRefBehavior
|
|
BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
|
|
if (CS.doesNotAccessMemory())
|
|
// Can't do better than this.
|
|
return DoesNotAccessMemory;
|
|
|
|
ModRefBehavior Min = UnknownModRefBehavior;
|
|
|
|
// If the callsite knows it only reads memory, don't return worse
|
|
// than that.
|
|
if (CS.onlyReadsMemory())
|
|
Min = OnlyReadsMemory;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
|
|
}
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given function.
|
|
/// For use when the call site is not known.
|
|
AliasAnalysis::ModRefBehavior
|
|
BasicAliasAnalysis::getModRefBehavior(const Function *F) {
|
|
// If the function declares it doesn't access memory, we can't do better.
|
|
if (F->doesNotAccessMemory())
|
|
return DoesNotAccessMemory;
|
|
|
|
// For intrinsics, we can check the table.
|
|
if (unsigned iid = F->getIntrinsicID()) {
|
|
#define GET_INTRINSIC_MODREF_BEHAVIOR
|
|
#include "llvm/IR/Intrinsics.gen"
|
|
#undef GET_INTRINSIC_MODREF_BEHAVIOR
|
|
}
|
|
|
|
ModRefBehavior Min = UnknownModRefBehavior;
|
|
|
|
// If the function declares it only reads memory, go with that.
|
|
if (F->onlyReadsMemory())
|
|
Min = OnlyReadsMemory;
|
|
|
|
const TargetLibraryInfo &TLI =
|
|
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
if (isMemsetPattern16(F, TLI))
|
|
Min = OnlyAccessesArgumentPointees;
|
|
|
|
// Otherwise be conservative.
|
|
return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
|
|
}
|
|
|
|
AliasAnalysis::Location
|
|
BasicAliasAnalysis::getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
|
|
ModRefResult &Mask) {
|
|
Location Loc = AliasAnalysis::getArgLocation(CS, ArgIdx, Mask);
|
|
const TargetLibraryInfo &TLI =
|
|
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
if (II != nullptr)
|
|
switch (II->getIntrinsicID()) {
|
|
default: break;
|
|
case Intrinsic::memset:
|
|
case Intrinsic::memcpy:
|
|
case Intrinsic::memmove: {
|
|
assert((ArgIdx == 0 || ArgIdx == 1) &&
|
|
"Invalid argument index for memory intrinsic");
|
|
if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
|
|
Loc.Size = LenCI->getZExtValue();
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Memory intrinsic location pointer not argument?");
|
|
Mask = ArgIdx ? Ref : Mod;
|
|
break;
|
|
}
|
|
case Intrinsic::lifetime_start:
|
|
case Intrinsic::lifetime_end:
|
|
case Intrinsic::invariant_start: {
|
|
assert(ArgIdx == 1 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
Loc.Size = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
|
|
break;
|
|
}
|
|
case Intrinsic::invariant_end: {
|
|
assert(ArgIdx == 2 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
Loc.Size = cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
|
|
break;
|
|
}
|
|
case Intrinsic::arm_neon_vld1: {
|
|
assert(ArgIdx == 0 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
// LLVM's vld1 and vst1 intrinsics currently only support a single
|
|
// vector register.
|
|
if (DL)
|
|
Loc.Size = DL->getTypeStoreSize(II->getType());
|
|
break;
|
|
}
|
|
case Intrinsic::arm_neon_vst1: {
|
|
assert(ArgIdx == 0 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
if (DL)
|
|
Loc.Size = DL->getTypeStoreSize(II->getArgOperand(1)->getType());
|
|
break;
|
|
}
|
|
}
|
|
|
|
// We can bound the aliasing properties of memset_pattern16 just as we can
|
|
// for memcpy/memset. This is particularly important because the
|
|
// LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
|
|
// whenever possible.
|
|
else if (CS.getCalledFunction() &&
|
|
isMemsetPattern16(CS.getCalledFunction(), TLI)) {
|
|
assert((ArgIdx == 0 || ArgIdx == 1) &&
|
|
"Invalid argument index for memset_pattern16");
|
|
if (ArgIdx == 1)
|
|
Loc.Size = 16;
|
|
else if (const ConstantInt *LenCI =
|
|
dyn_cast<ConstantInt>(CS.getArgument(2)))
|
|
Loc.Size = LenCI->getZExtValue();
|
|
assert(Loc.Ptr == CS.getArgument(ArgIdx) &&
|
|
"memset_pattern16 location pointer not argument?");
|
|
Mask = ArgIdx ? Ref : Mod;
|
|
}
|
|
// FIXME: Handle memset_pattern4 and memset_pattern8 also.
|
|
|
|
return Loc;
|
|
}
|
|
|
|
static bool isAssumeIntrinsic(ImmutableCallSite CS) {
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
if (II && II->getIntrinsicID() == Intrinsic::assume)
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
bool BasicAliasAnalysis::doInitialization(Module &M) {
|
|
InitializeAliasAnalysis(this, &M.getDataLayout());
|
|
return true;
|
|
}
|
|
|
|
/// getModRefInfo - Check to see if the specified callsite can clobber the
|
|
/// specified memory object. Since we only look at local properties of this
|
|
/// function, we really can't say much about this query. We do, however, use
|
|
/// simple "address taken" analysis on local objects.
|
|
AliasAnalysis::ModRefResult
|
|
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
|
|
const Location &Loc) {
|
|
assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
|
|
"AliasAnalysis query involving multiple functions!");
|
|
|
|
const Value *Object = GetUnderlyingObject(Loc.Ptr, *DL);
|
|
|
|
// If this is a tail call and Loc.Ptr points to a stack location, we know that
|
|
// the tail call cannot access or modify the local stack.
|
|
// We cannot exclude byval arguments here; these belong to the caller of
|
|
// the current function not to the current function, and a tail callee
|
|
// may reference them.
|
|
if (isa<AllocaInst>(Object))
|
|
if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
|
|
if (CI->isTailCall())
|
|
return NoModRef;
|
|
|
|
// If the pointer is to a locally allocated object that does not escape,
|
|
// then the call can not mod/ref the pointer unless the call takes the pointer
|
|
// as an argument, and itself doesn't capture it.
|
|
if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
|
|
isNonEscapingLocalObject(Object)) {
|
|
bool PassedAsArg = false;
|
|
unsigned ArgNo = 0;
|
|
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(Location(*CI), Location(Object))) {
|
|
PassedAsArg = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (!PassedAsArg)
|
|
return NoModRef;
|
|
}
|
|
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isAssumeIntrinsic(CS))
|
|
return NoModRef;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return AliasAnalysis::getModRefInfo(CS, Loc);
|
|
}
|
|
|
|
AliasAnalysis::ModRefResult
|
|
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
|
|
ImmutableCallSite CS2) {
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isAssumeIntrinsic(CS1) || isAssumeIntrinsic(CS2))
|
|
return NoModRef;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return AliasAnalysis::getModRefInfo(CS1, CS2);
|
|
}
|
|
|
|
/// \brief Provide ad-hoc rules to disambiguate accesses through two GEP
|
|
/// operators, both having the exact same pointer operand.
|
|
static AliasAnalysis::AliasResult
|
|
aliasSameBasePointerGEPs(const GEPOperator *GEP1, uint64_t V1Size,
|
|
const GEPOperator *GEP2, uint64_t V2Size,
|
|
const DataLayout &DL) {
|
|
|
|
assert(GEP1->getPointerOperand() == GEP2->getPointerOperand() &&
|
|
"Expected GEPs with the same pointer operand");
|
|
|
|
// Try to determine whether GEP1 and GEP2 index through arrays, into structs,
|
|
// such that the struct field accesses provably cannot alias.
|
|
// We also need at least two indices (the pointer, and the struct field).
|
|
if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
|
|
GEP1->getNumIndices() < 2)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// If we don't know the size of the accesses through both GEPs, we can't
|
|
// determine whether the struct fields accessed can't alias.
|
|
if (V1Size == AliasAnalysis::UnknownSize ||
|
|
V2Size == AliasAnalysis::UnknownSize)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
ConstantInt *C1 =
|
|
dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1));
|
|
ConstantInt *C2 =
|
|
dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1));
|
|
|
|
// If the last (struct) indices aren't constants, we can't say anything.
|
|
// If they're identical, the other indices might be also be dynamically
|
|
// equal, so the GEPs can alias.
|
|
if (!C1 || !C2 || C1 == C2)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// Find the last-indexed type of the GEP, i.e., the type you'd get if
|
|
// you stripped the last index.
|
|
// On the way, look at each indexed type. If there's something other
|
|
// than an array, different indices can lead to different final types.
|
|
SmallVector<Value *, 8> IntermediateIndices;
|
|
|
|
// Insert the first index; we don't need to check the type indexed
|
|
// through it as it only drops the pointer indirection.
|
|
assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine");
|
|
IntermediateIndices.push_back(GEP1->getOperand(1));
|
|
|
|
// Insert all the remaining indices but the last one.
|
|
// Also, check that they all index through arrays.
|
|
for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) {
|
|
if (!isa<ArrayType>(GetElementPtrInst::getIndexedType(
|
|
GEP1->getSourceElementType(), IntermediateIndices)))
|
|
return AliasAnalysis::MayAlias;
|
|
IntermediateIndices.push_back(GEP1->getOperand(i + 1));
|
|
}
|
|
|
|
StructType *LastIndexedStruct =
|
|
dyn_cast<StructType>(GetElementPtrInst::getIndexedType(
|
|
GEP1->getSourceElementType(), IntermediateIndices));
|
|
|
|
if (!LastIndexedStruct)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// We know that:
|
|
// - both GEPs begin indexing from the exact same pointer;
|
|
// - the last indices in both GEPs are constants, indexing into a struct;
|
|
// - said indices are different, hence, the pointed-to fields are different;
|
|
// - both GEPs only index through arrays prior to that.
|
|
//
|
|
// This lets us determine that the struct that GEP1 indexes into and the
|
|
// struct that GEP2 indexes into must either precisely overlap or be
|
|
// completely disjoint. Because they cannot partially overlap, indexing into
|
|
// different non-overlapping fields of the struct will never alias.
|
|
|
|
// Therefore, the only remaining thing needed to show that both GEPs can't
|
|
// alias is that the fields are not overlapping.
|
|
const StructLayout *SL = DL.getStructLayout(LastIndexedStruct);
|
|
const uint64_t StructSize = SL->getSizeInBytes();
|
|
const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue());
|
|
const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue());
|
|
|
|
auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size,
|
|
uint64_t V2Off, uint64_t V2Size) {
|
|
return V1Off < V2Off && V1Off + V1Size <= V2Off &&
|
|
((V2Off + V2Size <= StructSize) ||
|
|
(V2Off + V2Size - StructSize <= V1Off));
|
|
};
|
|
|
|
if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) ||
|
|
EltsDontOverlap(V2Off, V2Size, V1Off, V1Size))
|
|
return AliasAnalysis::NoAlias;
|
|
|
|
return AliasAnalysis::MayAlias;
|
|
}
|
|
|
|
bool BasicAliasAnalysis::constantOffsetHeuristic(
|
|
const SmallVectorImpl<VariableGEPIndex> &VarIndices, uint64_t V1Size,
|
|
uint64_t V2Size, int64_t BaseOffset, const DataLayout *DL,
|
|
AssumptionCache *AC, DominatorTree *DT) {
|
|
if (VarIndices.size() != 2 || V1Size == UnknownSize ||
|
|
V2Size == UnknownSize || !DL)
|
|
return false;
|
|
|
|
const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1];
|
|
|
|
if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits ||
|
|
Var0.Scale != -Var1.Scale)
|
|
return false;
|
|
|
|
unsigned Width = Var1.V->getType()->getIntegerBitWidth();
|
|
|
|
// We'll strip off the Extensions of Var0 and Var1 and do another round
|
|
// of GetLinearExpression decomposition. In the example above, if Var0
|
|
// is zext(%x + 1) we should get V1 == %x and V1Offset == 1.
|
|
|
|
APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 1),
|
|
V1Offset(Width, 1);
|
|
bool NSW = true, NUW = true;
|
|
unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0;
|
|
const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits,
|
|
V0SExtBits, *DL, 0, AC, DT, NSW, NUW);
|
|
NSW = true, NUW = true;
|
|
const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits,
|
|
V1SExtBits, *DL, 0, AC, DT, NSW, NUW);
|
|
|
|
if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits ||
|
|
V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1))
|
|
return false;
|
|
|
|
// We have a hit - Var0 and Var1 only differ by a constant offset!
|
|
|
|
// If we've been sext'ed then zext'd the maximum difference between Var0 and
|
|
// Var1 is possible to calculate, but we're just interested in the absolute
|
|
// minumum difference between the two. The minimum distance may occur due to
|
|
// wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so
|
|
// the minimum distance between %i and %i + 5 is 3.
|
|
APInt MinDiff = V0Offset - V1Offset,
|
|
Wrapped = APInt::getMaxValue(Width) - MinDiff + APInt(Width, 1);
|
|
MinDiff = APIntOps::umin(MinDiff, Wrapped);
|
|
uint64_t MinDiffBytes = MinDiff.getZExtValue() * std::abs(Var0.Scale);
|
|
|
|
// We can't definitely say whether GEP1 is before or after V2 due to wrapping
|
|
// arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other
|
|
// values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and
|
|
// V2Size can fit in the MinDiffBytes gap.
|
|
return V1Size + std::abs(BaseOffset) <= MinDiffBytes &&
|
|
V2Size + std::abs(BaseOffset) <= MinDiffBytes;
|
|
}
|
|
|
|
/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
|
|
/// against another pointer. We know that V1 is a GEP, but we don't know
|
|
/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL),
|
|
/// UnderlyingV2 is the same for V2.
|
|
///
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
|
|
const AAMDNodes &V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo,
|
|
const Value *UnderlyingV1,
|
|
const Value *UnderlyingV2) {
|
|
int64_t GEP1BaseOffset;
|
|
bool GEP1MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
|
|
|
|
// We have to get two AssumptionCaches here because GEP1 and V2 may be from
|
|
// different functions.
|
|
// FIXME: This really doesn't make any sense. We get a dominator tree below
|
|
// that can only refer to a single function. But this function (aliasGEP) is
|
|
// a method on an immutable pass that can be called when there *isn't*
|
|
// a single function. The old pass management layer makes this "work", but
|
|
// this isn't really a clean solution.
|
|
AssumptionCacheTracker &ACT = getAnalysis<AssumptionCacheTracker>();
|
|
AssumptionCache *AC1 = nullptr, *AC2 = nullptr;
|
|
if (auto *GEP1I = dyn_cast<Instruction>(GEP1))
|
|
AC1 = &ACT.getAssumptionCache(
|
|
const_cast<Function &>(*GEP1I->getParent()->getParent()));
|
|
if (auto *I2 = dyn_cast<Instruction>(V2))
|
|
AC2 = &ACT.getAssumptionCache(
|
|
const_cast<Function &>(*I2->getParent()->getParent()));
|
|
|
|
DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
|
|
DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
|
|
|
|
// If we have two gep instructions with must-alias or not-alias'ing base
|
|
// pointers, figure out if the indexes to the GEP tell us anything about the
|
|
// derived pointer.
|
|
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
|
|
// Do the base pointers alias?
|
|
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, AAMDNodes(),
|
|
UnderlyingV2, UnknownSize, AAMDNodes());
|
|
|
|
// Check for geps of non-aliasing underlying pointers where the offsets are
|
|
// identical.
|
|
if ((BaseAlias == MayAlias) && V1Size == V2Size) {
|
|
// Do the base pointers alias assuming type and size.
|
|
AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
|
|
V1AAInfo, UnderlyingV2,
|
|
V2Size, V2AAInfo);
|
|
if (PreciseBaseAlias == NoAlias) {
|
|
// See if the computed offset from the common pointer tells us about the
|
|
// relation of the resulting pointer.
|
|
int64_t GEP2BaseOffset;
|
|
bool GEP2MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
|
|
const Value *GEP2BasePtr =
|
|
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
|
|
GEP2MaxLookupReached, *DL, AC2, DT);
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, *DL, AC1, DT);
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Same offsets.
|
|
if (GEP1BaseOffset == GEP2BaseOffset &&
|
|
GEP1VariableIndices == GEP2VariableIndices)
|
|
return NoAlias;
|
|
GEP1VariableIndices.clear();
|
|
}
|
|
}
|
|
|
|
// If we get a No or May, then return it immediately, no amount of analysis
|
|
// will improve this situation.
|
|
if (BaseAlias != MustAlias) return BaseAlias;
|
|
|
|
// Otherwise, we have a MustAlias. Since the base pointers alias each other
|
|
// exactly, see if the computed offset from the common pointer tells us
|
|
// about the relation of the resulting pointer.
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, *DL, AC1, DT);
|
|
|
|
int64_t GEP2BaseOffset;
|
|
bool GEP2MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
|
|
const Value *GEP2BasePtr =
|
|
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
|
|
GEP2MaxLookupReached, *DL, AC2, DT);
|
|
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
|
|
// If we know the two GEPs are based off of the exact same pointer (and not
|
|
// just the same underlying object), see if that tells us anything about
|
|
// the resulting pointers.
|
|
if (DL && GEP1->getPointerOperand() == GEP2->getPointerOperand()) {
|
|
AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, *DL);
|
|
// If we couldn't find anything interesting, don't abandon just yet.
|
|
if (R != MayAlias)
|
|
return R;
|
|
}
|
|
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
|
|
// symbolic difference.
|
|
GEP1BaseOffset -= GEP2BaseOffset;
|
|
GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
|
|
|
|
} else {
|
|
// Check to see if these two pointers are related by the getelementptr
|
|
// instruction. If one pointer is a GEP with a non-zero index of the other
|
|
// pointer, we know they cannot alias.
|
|
|
|
// If both accesses are unknown size, we can't do anything useful here.
|
|
if (V1Size == UnknownSize && V2Size == UnknownSize)
|
|
return MayAlias;
|
|
|
|
AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, AAMDNodes(),
|
|
V2, V2Size, V2AAInfo);
|
|
if (R != MustAlias)
|
|
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
|
|
// If V2 is known not to alias GEP base pointer, then the two values
|
|
// cannot alias per GEP semantics: "A pointer value formed from a
|
|
// getelementptr instruction is associated with the addresses associated
|
|
// with the first operand of the getelementptr".
|
|
return R;
|
|
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, *DL, AC1, DT);
|
|
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
}
|
|
|
|
// In the two GEP Case, if there is no difference in the offsets of the
|
|
// computed pointers, the resultant pointers are a must alias. This
|
|
// hapens when we have two lexically identical GEP's (for example).
|
|
//
|
|
// In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
|
|
// must aliases the GEP, the end result is a must alias also.
|
|
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
|
|
return MustAlias;
|
|
|
|
// If there is a constant difference between the pointers, but the difference
|
|
// is less than the size of the associated memory object, then we know
|
|
// that the objects are partially overlapping. If the difference is
|
|
// greater, we know they do not overlap.
|
|
if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
|
|
if (GEP1BaseOffset >= 0) {
|
|
if (V2Size != UnknownSize) {
|
|
if ((uint64_t)GEP1BaseOffset < V2Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
} else {
|
|
// We have the situation where:
|
|
// + +
|
|
// | BaseOffset |
|
|
// ---------------->|
|
|
// |-->V1Size |-------> V2Size
|
|
// GEP1 V2
|
|
// We need to know that V2Size is not unknown, otherwise we might have
|
|
// stripped a gep with negative index ('gep <ptr>, -1, ...).
|
|
if (V1Size != UnknownSize && V2Size != UnknownSize) {
|
|
if (-(uint64_t)GEP1BaseOffset < V1Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (!GEP1VariableIndices.empty()) {
|
|
uint64_t Modulo = 0;
|
|
bool AllPositive = true;
|
|
for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) {
|
|
|
|
// Try to distinguish something like &A[i][1] against &A[42][0].
|
|
// Grab the least significant bit set in any of the scales. We
|
|
// don't need std::abs here (even if the scale's negative) as we'll
|
|
// be ^'ing Modulo with itself later.
|
|
Modulo |= (uint64_t) GEP1VariableIndices[i].Scale;
|
|
|
|
if (AllPositive) {
|
|
// If the Value could change between cycles, then any reasoning about
|
|
// the Value this cycle may not hold in the next cycle. We'll just
|
|
// give up if we can't determine conditions that hold for every cycle:
|
|
const Value *V = GEP1VariableIndices[i].V;
|
|
|
|
bool SignKnownZero, SignKnownOne;
|
|
ComputeSignBit(const_cast<Value *>(V), SignKnownZero, SignKnownOne, *DL,
|
|
0, AC1, nullptr, DT);
|
|
|
|
// Zero-extension widens the variable, and so forces the sign
|
|
// bit to zero.
|
|
bool IsZExt = GEP1VariableIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
|
|
SignKnownZero |= IsZExt;
|
|
SignKnownOne &= !IsZExt;
|
|
|
|
// If the variable begins with a zero then we know it's
|
|
// positive, regardless of whether the value is signed or
|
|
// unsigned.
|
|
int64_t Scale = GEP1VariableIndices[i].Scale;
|
|
AllPositive =
|
|
(SignKnownZero && Scale >= 0) ||
|
|
(SignKnownOne && Scale < 0);
|
|
}
|
|
}
|
|
|
|
Modulo = Modulo ^ (Modulo & (Modulo - 1));
|
|
|
|
// We can compute the difference between the two addresses
|
|
// mod Modulo. Check whether that difference guarantees that the
|
|
// two locations do not alias.
|
|
uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
|
|
if (V1Size != UnknownSize && V2Size != UnknownSize &&
|
|
ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
|
|
return NoAlias;
|
|
|
|
// If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
|
|
// If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
|
|
// don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
|
|
if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t) GEP1BaseOffset)
|
|
return NoAlias;
|
|
|
|
if (constantOffsetHeuristic(GEP1VariableIndices, V1Size, V2Size,
|
|
GEP1BaseOffset, DL, AC1, DT))
|
|
return NoAlias;
|
|
}
|
|
|
|
// Statically, we can see that the base objects are the same, but the
|
|
// pointers have dynamic offsets which we can't resolve. And none of our
|
|
// little tricks above worked.
|
|
//
|
|
// TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
|
|
// practical effect of this is protecting TBAA in the case of dynamic
|
|
// indices into arrays of unions or malloc'd memory.
|
|
return PartialAlias;
|
|
}
|
|
|
|
static AliasAnalysis::AliasResult
|
|
MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
|
|
// If the results agree, take it.
|
|
if (A == B)
|
|
return A;
|
|
// A mix of PartialAlias and MustAlias is PartialAlias.
|
|
if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
|
|
(B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
|
|
return AliasAnalysis::PartialAlias;
|
|
// Otherwise, we don't know anything.
|
|
return AliasAnalysis::MayAlias;
|
|
}
|
|
|
|
/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
|
|
/// instruction against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const AAMDNodes &SIAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo) {
|
|
// If the values are Selects with the same condition, we can do a more precise
|
|
// check: just check for aliases between the values on corresponding arms.
|
|
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
|
|
if (SI->getCondition() == SI2->getCondition()) {
|
|
AliasResult Alias =
|
|
aliasCheck(SI->getTrueValue(), SISize, SIAAInfo,
|
|
SI2->getTrueValue(), V2Size, V2AAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize, SIAAInfo,
|
|
SI2->getFalseValue(), V2Size, V2AAInfo);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// If both arms of the Select node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
AliasResult Alias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
AliasResult ThisAlias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
|
|
// against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const AAMDNodes &PNAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo) {
|
|
// Track phi nodes we have visited. We use this information when we determine
|
|
// value equivalence.
|
|
VisitedPhiBBs.insert(PN->getParent());
|
|
|
|
// If the values are PHIs in the same block, we can do a more precise
|
|
// as well as efficient check: just check for aliases between the values
|
|
// on corresponding edges.
|
|
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
|
|
if (PN2->getParent() == PN->getParent()) {
|
|
LocPair Locs(Location(PN, PNSize, PNAAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
if (PN > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
// Analyse the PHIs' inputs under the assumption that the PHIs are
|
|
// NoAlias.
|
|
// If the PHIs are May/MustAlias there must be (recursively) an input
|
|
// operand from outside the PHIs' cycle that is MayAlias/MustAlias or
|
|
// there must be an operation on the PHIs within the PHIs' value cycle
|
|
// that causes a MayAlias.
|
|
// Pretend the phis do not alias.
|
|
AliasResult Alias = NoAlias;
|
|
assert(AliasCache.count(Locs) &&
|
|
"There must exist an entry for the phi node");
|
|
AliasResult OrigAliasResult = AliasCache[Locs];
|
|
AliasCache[Locs] = NoAlias;
|
|
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias =
|
|
aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
|
|
V2Size, V2AAInfo);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
// Reset if speculation failed.
|
|
if (Alias != NoAlias)
|
|
AliasCache[Locs] = OrigAliasResult;
|
|
|
|
return Alias;
|
|
}
|
|
|
|
SmallPtrSet<Value*, 4> UniqueSrc;
|
|
SmallVector<Value*, 4> V1Srcs;
|
|
for (Value *PV1 : PN->incoming_values()) {
|
|
if (isa<PHINode>(PV1))
|
|
// If any of the source itself is a PHI, return MayAlias conservatively
|
|
// to avoid compile time explosion. The worst possible case is if both
|
|
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
|
|
// and 'n' are the number of PHI sources.
|
|
return MayAlias;
|
|
if (UniqueSrc.insert(PV1).second)
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
|
|
AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo,
|
|
V1Srcs[0], PNSize, PNAAInfo);
|
|
// Early exit if the check of the first PHI source against V2 is MayAlias.
|
|
// Other results are not possible.
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
|
|
Value *V = V1Srcs[i];
|
|
|
|
AliasResult ThisAlias = aliasCheck(V2, V2Size, V2AAInfo,
|
|
V, PNSize, PNAAInfo);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
return Alias;
|
|
}
|
|
|
|
// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
|
|
// such as array references.
|
|
//
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
|
|
AAMDNodes V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
AAMDNodes V2AAInfo) {
|
|
// If either of the memory references is empty, it doesn't matter what the
|
|
// pointer values are.
|
|
if (V1Size == 0 || V2Size == 0)
|
|
return NoAlias;
|
|
|
|
// Strip off any casts if they exist.
|
|
V1 = V1->stripPointerCasts();
|
|
V2 = V2->stripPointerCasts();
|
|
|
|
// If V1 or V2 is undef, the result is NoAlias because we can always pick a
|
|
// value for undef that aliases nothing in the program.
|
|
if (isa<UndefValue>(V1) || isa<UndefValue>(V2))
|
|
return NoAlias;
|
|
|
|
// Are we checking for alias of the same value?
|
|
// Because we look 'through' phi nodes we could look at "Value" pointers from
|
|
// different iterations. We must therefore make sure that this is not the
|
|
// case. The function isValueEqualInPotentialCycles ensures that this cannot
|
|
// happen by looking at the visited phi nodes and making sure they cannot
|
|
// reach the value.
|
|
if (isValueEqualInPotentialCycles(V1, V2))
|
|
return MustAlias;
|
|
|
|
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
|
|
return NoAlias; // Scalars cannot alias each other
|
|
|
|
// Figure out what objects these things are pointing to if we can.
|
|
const Value *O1 = GetUnderlyingObject(V1, *DL, MaxLookupSearchDepth);
|
|
const Value *O2 = GetUnderlyingObject(V2, *DL, MaxLookupSearchDepth);
|
|
|
|
// Null values in the default address space don't point to any object, so they
|
|
// don't alias any other pointer.
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
|
|
if (O1 != O2) {
|
|
// If V1/V2 point to two different objects we know that we have no alias.
|
|
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
|
|
return NoAlias;
|
|
|
|
// Constant pointers can't alias with non-const isIdentifiedObject objects.
|
|
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
|
|
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
|
|
return NoAlias;
|
|
|
|
// Function arguments can't alias with things that are known to be
|
|
// unambigously identified at the function level.
|
|
if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
|
|
(isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
|
|
return NoAlias;
|
|
|
|
// Most objects can't alias null.
|
|
if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
|
|
(isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
|
|
return NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object within the same function, then we know the
|
|
// object couldn't escape to a point where the call could return it.
|
|
//
|
|
// Note that if the pointers are in different functions, there are a
|
|
// variety of complications. A call with a nocapture argument may still
|
|
// temporary store the nocapture argument's value in a temporary memory
|
|
// location if that memory location doesn't escape. Or it may pass a
|
|
// nocapture value to other functions as long as they don't capture it.
|
|
if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
|
|
return NoAlias;
|
|
if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
|
|
return NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
if (DL)
|
|
if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
|
|
(V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
|
|
return NoAlias;
|
|
|
|
// Check the cache before climbing up use-def chains. This also terminates
|
|
// otherwise infinitely recursive queries.
|
|
LocPair Locs(Location(V1, V1Size, V1AAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
if (V1 > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
std::pair<AliasCacheTy::iterator, bool> Pair =
|
|
AliasCache.insert(std::make_pair(Locs, MayAlias));
|
|
if (!Pair.second)
|
|
return Pair.first->second;
|
|
|
|
// FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
|
|
// GEP can't simplify, we don't even look at the PHI cases.
|
|
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(O1, O2);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
|
|
AliasResult Result = aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
|
|
AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo,
|
|
V2, V2Size, V2AAInfo);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
|
|
AliasResult Result = aliasSelect(S1, V1Size, V1AAInfo,
|
|
V2, V2Size, V2AAInfo);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
// If both pointers are pointing into the same object and one of them
|
|
// accesses is accessing the entire object, then the accesses must
|
|
// overlap in some way.
|
|
if (DL && O1 == O2)
|
|
if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) ||
|
|
(V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI)))
|
|
return AliasCache[Locs] = PartialAlias;
|
|
|
|
AliasResult Result =
|
|
AliasAnalysis::alias(Location(V1, V1Size, V1AAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
|
|
const Value *V2) {
|
|
if (V != V2)
|
|
return false;
|
|
|
|
const Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.empty())
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
|
|
return false;
|
|
|
|
// Use dominance or loop info if available.
|
|
DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
|
|
DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
|
|
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
|
|
LoopInfo *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
|
|
|
|
// Make sure that the visited phis cannot reach the Value. This ensures that
|
|
// the Values cannot come from different iterations of a potential cycle the
|
|
// phi nodes could be involved in.
|
|
for (auto *P : VisitedPhiBBs)
|
|
if (isPotentiallyReachable(P->begin(), Inst, DT, LI))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// GetIndexDifference - Dest and Src are the variable indices from two
|
|
/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
|
|
/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
|
|
/// difference between the two pointers.
|
|
void BasicAliasAnalysis::GetIndexDifference(
|
|
SmallVectorImpl<VariableGEPIndex> &Dest,
|
|
const SmallVectorImpl<VariableGEPIndex> &Src) {
|
|
if (Src.empty())
|
|
return;
|
|
|
|
for (unsigned i = 0, e = Src.size(); i != e; ++i) {
|
|
const Value *V = Src[i].V;
|
|
unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits;
|
|
int64_t Scale = Src[i].Scale;
|
|
|
|
// Find V in Dest. This is N^2, but pointer indices almost never have more
|
|
// than a few variable indexes.
|
|
for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
|
|
if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
|
|
Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits)
|
|
continue;
|
|
|
|
// If we found it, subtract off Scale V's from the entry in Dest. If it
|
|
// goes to zero, remove the entry.
|
|
if (Dest[j].Scale != Scale)
|
|
Dest[j].Scale -= Scale;
|
|
else
|
|
Dest.erase(Dest.begin() + j);
|
|
Scale = 0;
|
|
break;
|
|
}
|
|
|
|
// If we didn't consume this entry, add it to the end of the Dest list.
|
|
if (Scale) {
|
|
VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
|
|
Dest.push_back(Entry);
|
|
}
|
|
}
|
|
}
|