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Revert r241981 "Revert "Revert r236894 "[BasicAA] Fix zext & sext handling"""

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The repros from PR23626 still fail.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242025 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manuel Klimek
2015-07-13 13:50:55 +00:00
parent a0a51734cd
commit c376473bb4
3 changed files with 58 additions and 394 deletions
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255
lib/Analysis/BasicAliasAnalysis.cpp
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@ -162,26 +162,20 @@ static bool isObjectSize(const Value *V, uint64_t Size,
//===----------------------------------------------------------------------===//
namespace {
enum ExtensionKind {
EK_NotExtended,
EK_SignExt,
EK_ZeroExt
};
// 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;
ExtensionKind Extension;
int64_t Scale;
bool operator==(const VariableGEPIndex &Other) const {
return V == Other.V && ZExtBits == Other.ZExtBits &&
SExtBits == Other.SExtBits && Scale == Other.Scale;
return V == Other.V && Extension == Other.Extension &&
Scale == Other.Scale;
}
bool operator!=(const VariableGEPIndex &Other) const {
@ -199,12 +193,10 @@ namespace {
///
/// 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) {
static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
ExtensionKind &Extension,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, DominatorTree *DT) {
assert(V->getType()->isIntegerTy() && "Not an integer value");
// Limit our recursion depth.
@ -214,32 +206,18 @@ static const Value *GetLinearExpression(const Value *V, APInt &Scale,
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());
if (ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
// if it's a constant, just convert it to an offset
// and remove the variable.
Offset += Const->getValue();
assert(Scale == 0 && "Constant values don't have a scale");
return V;
}
if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
if (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;
default: break;
case Instruction::Or:
// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
// analyze it.
@ -248,88 +226,45 @@ static const Value *GetLinearExpression(const Value *V, APInt &Scale,
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;
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
DL, Depth + 1, AC, DT);
Offset += RHSC->getValue();
return V;
case Instruction::Mul:
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
Offset *= RHS;
Scale *= RHS;
break;
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
DL, Depth + 1, AC, DT);
Offset *= RHSC->getValue();
Scale *= RHSC->getValue();
return V;
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;
V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
DL, Depth + 1, AC, DT);
Offset <<= RHSC->getValue().getLimitedValue();
Scale <<= RHSC->getValue().getLimitedValue();
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)) {
if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
(isa<ZExtInst>(V) && Extension != EK_SignExt)) {
Value *CastOp = cast<CastInst>(V)->getOperand(0);
unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
unsigned OldWidth = Scale.getBitWidth();
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);
Scale = Scale.trunc(SmallWidth);
Offset = Offset.trunc(SmallWidth);
Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
// 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;
Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL,
Depth + 1, AC, DT);
Scale = Scale.zext(OldWidth);
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;
}
// We have to sign-extend even if Extension == EK_ZeroExt as we can't
// decompose a sign extension (i.e. zext(x - 1) != zext(x) - zext(-1)).
Offset = Offset.sext(OldWidth);
return Result;
}
@ -411,7 +346,7 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
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;
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.
@ -423,27 +358,25 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
}
// For an array/pointer, add the element offset, explicitly scaled.
if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
if (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;
ExtensionKind Extension = EK_NotExtended;
// 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;
if (DL.getPointerSizeInBits(AS) > Width)
Extension = EK_SignExt;
// 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);
Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, DL,
0, AC, DT);
// 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.
@ -455,8 +388,8 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
// 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) {
if (VarIndices[i].V == Index &&
VarIndices[i].Extension == Extension) {
Scale += VarIndices[i].Scale;
VarIndices.erase(VarIndices.begin()+i);
break;
@ -465,13 +398,13 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
// Make sure that we have a scale that makes sense for this target's
// pointer size.
if (unsigned ShiftBits = 64 - PointerSize) {
if (unsigned ShiftBits = 64 - DL.getPointerSizeInBits(AS)) {
Scale <<= ShiftBits;
Scale = (int64_t)Scale >> ShiftBits;
}
if (Scale) {
VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
VariableGEPIndex Entry = {Index, Extension,
static_cast<int64_t>(Scale)};
VarIndices.push_back(Entry);
}
@ -607,20 +540,6 @@ namespace {
/// 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
@ -1017,60 +936,6 @@ static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
return 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 == MemoryLocation::UnknownSize ||
V2Size == MemoryLocation::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, 0),
V1Offset(Width, 0);
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),
@ -1293,7 +1158,7 @@ AliasResult BasicAliasAnalysis::aliasGEP(
// Zero-extension widens the variable, and so forces the sign
// bit to zero.
bool IsZExt = GEP1VariableIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt;
SignKnownZero |= IsZExt;
SignKnownOne &= !IsZExt;
@ -1323,10 +1188,6 @@ AliasResult BasicAliasAnalysis::aliasGEP(
// 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
@ -1666,14 +1527,14 @@ void BasicAliasAnalysis::GetIndexDifference(
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;
ExtensionKind Extension = Src[i].Extension;
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)
Dest[j].Extension != Extension)
continue;
// If we found it, subtract off Scale V's from the entry in Dest. If it
@ -1688,7 +1549,7 @@ void BasicAliasAnalysis::GetIndexDifference(
// If we didn't consume this entry, add it to the end of the Dest list.
if (Scale) {
VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
VariableGEPIndex Entry = { V, Extension, -Scale };
Dest.push_back(Entry);
}
}