[llvm] r246502 - [BasicAA] Fix the handling of sext and zext in the analysis of GEPs.
Hans Wennborg via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 31 16:04:35 PDT 2015
The tag for 3.7.0 was committed last Friday, so it's too late for
that, but it seems like a good candidate for 3.7.1.
I'm putting it on my list and will let Tom know about it when he
starts the 3.7.1 process.
On Mon, Aug 31, 2015 at 3:40 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> Hi Hans,
>
> Following Hal's recommendation in D11847, I think we want to pull that into 3.7.
>
> Thanks,
> -Quentin
>> On Aug 31, 2015, at 3:32 PM, Quentin Colombet via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>>
>> Author: qcolombet
>> Date: Mon Aug 31 17:32:47 2015
>> New Revision: 246502
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=246502&view=rev
>> Log:
>> [BasicAA] Fix the handling of sext and zext in the analysis of GEPs.
>> Hopefully this will end the GEPs saga!
>>
>> This commit reverts r245394, i.e., it reapplies r221876 while incorporating the
>> fixes from D11847.
>> r221876 was not reapplied alone because it was not safe and D11847 was not
>> applied alone because it needs r221876 to produce correct results.
>>
>> This should fix PR24596.
>>
>> Original commit message for r221876:
>> Let's try this again...
>>
>> This reverts r219432, plus a bug fix.
>>
>> Description of the bug in r219432 (by Nick):
>>
>> The bug was using AllPositive to break out of the loop; if the loop break
>> condition i != e is changed to i != e && AllPositive then the
>> test_modulo_analysis_with_global test I've added will fail as the Modulo will
>> be calculated incorrectly (as the last loop iteration is skipped, so Modulo
>> isn't updated with its Scale).
>>
>> Nick also adds this comment:
>>
>> ComputeSignBit is safe to use in loops as it takes into account phi nodes, and
>> the == EK_ZeroEx check is safe in loops as, no matter how the variable changes
>> between iterations, zero-extensions will always guarantee a zero sign bit. The
>> isValueEqualInPotentialCycles check is therefore definitely not needed as all
>> the variable analysis holds no matter how the variables change between loop
>> iterations.
>>
>> And this patch also adds another enhancement to GetLinearExpression - basically
>> to convert ConstantInts to Offsets (see test_const_eval and
>> test_const_eval_scaled for the situations this improves).
>>
>> Original commit message:
>>
>> This reverts r218944, which reverted r218714, plus a bug fix.
>>
>> Description of the bug in r218714 (by Nick):
>>
>> The original patch forgot to check if the Scale in VariableGEPIndex flipped the
>> sign of the variable. The BasicAA pass iterates over the instructions in the
>> order they appear in the function, and so BasicAliasAnalysis::aliasGEP is
>> called with the variable it first comes across as parameter GEP1. Adding a
>> %reorder label puts the definition of %a after %b so aliasGEP is called with %b
>> as the first parameter and %a as the second. aliasGEP later calculates that %a
>> == %b + 1 - %idxprom where %idxprom >= 0 (if %a was passed as the first
>> parameter it would calculate %b == %a - 1 + %idxprom where %idxprom >= 0) -
>> ignoring that %idxprom is scaled by -1 here lead the patch to incorrectly
>> conclude that %a > %b.
>>
>> Revised patch by Nick White, thanks! Thanks to Lang to isolating the bug.
>> Slightly modified by me to add an early exit from the loop and avoid
>> unnecessary, but expensive, function calls.
>>
>> Original commit message:
>>
>> Two related things:
>>
>> 1. Fixes a bug when calculating the offset in GetLinearExpression. The code
>> previously used zext to extend the offset, so negative offsets were converted
>> to large positive ones.
>>
>> 2. Enhance aliasGEP to deduce that, if the difference between two GEP
>> allocations is positive and all the variables that govern the offset are also
>> positive (i.e. the offset is strictly after the higher base pointer), then
>> locations that fit in the gap between the two base pointers are NoAlias.
>>
>> Patch by Nick White!
>>
>> Message from D11847:
>> Un-revert of r241981 and fix for PR23626. The 'Or' case of GetLinearExpression
>> delegates to 'Add' if possible, and if not it returns an Opaque value.
>> Unfortunately the Scale and Offsets weren't being set (and so defaulted to 0) -
>> and a scale of zero effectively removes the variable from the GEP instruction.
>> This meant that BasicAA would return MustAliases when it should have been
>> returning PartialAliases (and PR23626 was an example of the GVN pass using an
>> incorrect MustAlias to merge loads from what should have been different
>> pointers).
>>
>> Differential Revision: http://reviews.llvm.org/D11847
>> Patch by Nick White <n.j.white at gmail.com>!
>>
>>
>> Added:
>> llvm/trunk/test/Analysis/BasicAA/bug.23540.ll
>> llvm/trunk/test/Analysis/BasicAA/bug.23626.ll
>> llvm/trunk/test/Analysis/BasicAA/q.bad.ll
>> llvm/trunk/test/Analysis/BasicAA/zext.ll
>> - copied, changed from r245393, llvm/trunk/test/Analysis/BasicAA/zext.ll
>> Modified:
>> llvm/trunk/include/llvm/Analysis/BasicAliasAnalysis.h
>> llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> llvm/trunk/test/Analysis/BasicAA/phi-aa.ll
>>
>> Modified: llvm/trunk/include/llvm/Analysis/BasicAliasAnalysis.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/BasicAliasAnalysis.h?rev=246502&r1=246501&r2=246502&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Analysis/BasicAliasAnalysis.h (original)
>> +++ llvm/trunk/include/llvm/Analysis/BasicAliasAnalysis.h Mon Aug 31 17:32:47 2015
>> @@ -109,16 +109,25 @@ struct BasicAliasAnalysis : public Immut
>> }
>>
>> private:
>> - 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;
>> - ExtensionKind Extension;
>> +
>> + // 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 && Extension == Other.Extension &&
>> - Scale == Other.Scale;
>> + return V == Other.V && ZExtBits == Other.ZExtBits &&
>> + SExtBits == Other.SExtBits && Scale == Other.Scale;
>> }
>>
>> bool operator!=(const VariableGEPIndex &Other) const {
>> @@ -150,16 +159,30 @@ private:
>> /// Tracks instructions visited by pointsToConstantMemory.
>> SmallPtrSet<const Value *, 16> Visited;
>>
>> - static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
>> - ExtensionKind &Extension,
>> - const DataLayout &DL, unsigned Depth,
>> - AssumptionCache *AC, DominatorTree *DT);
>> + 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 const Value *
>> DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
>> SmallVectorImpl<VariableGEPIndex> &VarIndices,
>> bool &MaxLookupReached, const DataLayout &DL,
>> AssumptionCache *AC, DominatorTree *DT);
>> + /// \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);
>>
>> bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
>>
>>
>> Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=246502&r1=246501&r2=246502&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
>> +++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Mon Aug 31 17:32:47 2015
>> @@ -177,10 +177,10 @@ static bool isObjectSize(const Value *V,
>> ///
>> /// Note that this looks through extends, so the high bits may not be
>> /// represented in the result.
>> -/*static*/ Value *BasicAliasAnalysis::GetLinearExpression(
>> - Value *V, APInt &Scale, APInt &Offset, ExtensionKind &Extension,
>> - const DataLayout &DL, unsigned Depth, AssumptionCache *AC,
>> - DominatorTree *DT) {
>> +/*static*/ const Value *BasicAliasAnalysis::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.
>> @@ -190,55 +190,125 @@ static bool isObjectSize(const Value *V,
>> return V;
>> }
>>
>> - if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(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:
>> - break;
>> + // 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;
>> + BOp, DT)) {
>> + Scale = 1;
>> + Offset = 0;
>> + return V;
>> + }
>> // FALL THROUGH.
>> case Instruction::Add:
>> - V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
>> - DL, Depth + 1, AC, DT);
>> - Offset += RHSC->getValue();
>> - return V;
>> + 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, Extension,
>> - DL, Depth + 1, AC, DT);
>> - Offset *= RHSC->getValue();
>> - Scale *= RHSC->getValue();
>> - return V;
>> + 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, Extension,
>> - DL, Depth + 1, AC, DT);
>> - Offset <<= RHSC->getValue().getLimitedValue();
>> - Scale <<= RHSC->getValue().getLimitedValue();
>> + 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) && Extension != EK_ZeroExt) ||
>> - (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
>> + if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
>> Value *CastOp = cast<CastInst>(V)->getOperand(0);
>> - unsigned OldWidth = Scale.getBitWidth();
>> + unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
>> unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
>> - Scale = Scale.trunc(SmallWidth);
>> - Offset = Offset.trunc(SmallWidth);
>> - Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
>> -
>> - Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL,
>> - Depth + 1, AC, DT);
>> - Scale = Scale.zext(OldWidth);
>> - Offset = Offset.zext(OldWidth);
>> + 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;
>> }
>> @@ -318,7 +388,7 @@ static bool isObjectSize(const Value *V,
>> 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) {
>> - Value *Index = *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.
>> @@ -331,7 +401,7 @@ static bool isObjectSize(const Value *V,
>> }
>>
>> // For an array/pointer, add the element offset, explicitly scaled.
>> - if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
>> + if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
>> if (CIdx->isZero())
>> continue;
>> BaseOffs += DL.getTypeAllocSize(*GTI) * CIdx->getSExtValue();
>> @@ -339,18 +409,20 @@ static bool isObjectSize(const Value *V,
>> }
>>
>> uint64_t Scale = DL.getTypeAllocSize(*GTI);
>> - ExtensionKind Extension = EK_NotExtended;
>> + 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();
>> - if (DL.getPointerSizeInBits(AS) > Width)
>> - Extension = EK_SignExt;
>> + 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);
>> - Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, DL,
>> - 0, AC, DT);
>> + 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.
>> @@ -362,7 +434,8 @@ static bool isObjectSize(const Value *V,
>> // 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].Extension == Extension) {
>> + if (VarIndices[i].V == Index && VarIndices[i].ZExtBits == ZExtBits &&
>> + VarIndices[i].SExtBits == SExtBits) {
>> Scale += VarIndices[i].Scale;
>> VarIndices.erase(VarIndices.begin() + i);
>> break;
>> @@ -371,13 +444,13 @@ static bool isObjectSize(const Value *V,
>>
>> // Make sure that we have a scale that makes sense for this target's
>> // pointer size.
>> - if (unsigned ShiftBits = 64 - DL.getPointerSizeInBits(AS)) {
>> + if (unsigned ShiftBits = 64 - PointerSize) {
>> Scale <<= ShiftBits;
>> Scale = (int64_t)Scale >> ShiftBits;
>> }
>>
>> if (Scale) {
>> - VariableGEPIndex Entry = {Index, Extension,
>> + VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
>> static_cast<int64_t>(Scale)};
>> VarIndices.push_back(Entry);
>> }
>> @@ -948,12 +1021,42 @@ AliasResult BasicAliasAnalysis::aliasGEP
>> }
>> }
>>
>> - // Try to distinguish something like &A[i][1] against &A[42][0].
>> - // Grab the least significant bit set in any of the scales.
>> if (!GEP1VariableIndices.empty()) {
>> uint64_t Modulo = 0;
>> - for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
>> + 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
>> @@ -964,6 +1067,16 @@ AliasResult BasicAliasAnalysis::aliasGEP
>> V2Size != MemoryLocation::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
>> @@ -1333,14 +1446,14 @@ void BasicAliasAnalysis::GetIndexDiffere
>>
>> for (unsigned i = 0, e = Src.size(); i != e; ++i) {
>> const Value *V = Src[i].V;
>> - ExtensionKind Extension = Src[i].Extension;
>> + 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].Extension != Extension)
>> + 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
>> @@ -1355,8 +1468,62 @@ void BasicAliasAnalysis::GetIndexDiffere
>>
>> // If we didn't consume this entry, add it to the end of the Dest list.
>> if (Scale) {
>> - VariableGEPIndex Entry = {V, Extension, -Scale};
>> + VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
>> Dest.push_back(Entry);
>> }
>> }
>> }
>> +
>> +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;
>> +}
>>
>> Added: llvm/trunk/test/Analysis/BasicAA/bug.23540.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/bug.23540.ll?rev=246502&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/bug.23540.ll (added)
>> +++ llvm/trunk/test/Analysis/BasicAA/bug.23540.ll Mon Aug 31 17:32:47 2015
>> @@ -0,0 +1,17 @@
>> +; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
>> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>> +target triple = "x86_64-unknown-linux-gnu"
>> +
>> + at c = external global i32
>> +
>> +; CHECK-LABEL: f
>> +; CHECK: PartialAlias: i32* %arrayidx, i32* %arrayidx6
>> +define void @f() {
>> + %idxprom = zext i32 undef to i64
>> + %add4 = add i32 0, 1
>> + %idxprom5 = zext i32 %add4 to i64
>> + %arrayidx6 = getelementptr inbounds i32, i32* @c, i64 %idxprom5
>> + %arrayidx = getelementptr inbounds i32, i32* @c, i64 %idxprom
>> + ret void
>> +}
>> +
>>
>> Added: llvm/trunk/test/Analysis/BasicAA/bug.23626.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/bug.23626.ll?rev=246502&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/bug.23626.ll (added)
>> +++ llvm/trunk/test/Analysis/BasicAA/bug.23626.ll Mon Aug 31 17:32:47 2015
>> @@ -0,0 +1,31 @@
>> +; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
>> +target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
>> +target triple = "x86_64-apple-darwin13.4.0"
>> +
>> +; CHECK-LABEL: compute1
>> +; CHECK: PartialAlias: i32* %arrayidx8, i32* %out
>> +; CHECK: PartialAlias: i32* %arrayidx11, i32* %out
>> +; CHECK: PartialAlias: i32* %arrayidx11, i32* %arrayidx8
>> +; CHECK: PartialAlias: i32* %arrayidx14, i32* %out
>> +; CHECK: PartialAlias: i32* %arrayidx14, i32* %arrayidx8
>> +; CHECK: PartialAlias: i32* %arrayidx11, i32* %arrayidx14
>> +define void @compute1(i32 %num.0.lcssa, i32* %out) {
>> + %idxprom = zext i32 %num.0.lcssa to i64
>> + %arrayidx8 = getelementptr inbounds i32, i32* %out, i64 %idxprom
>> + %add9 = or i32 %num.0.lcssa, 1
>> + %idxprom10 = zext i32 %add9 to i64
>> + %arrayidx11 = getelementptr inbounds i32, i32* %out, i64 %idxprom10
>> + %add12 = or i32 %num.0.lcssa, 2
>> + %idxprom13 = zext i32 %add12 to i64
>> + %arrayidx14 = getelementptr inbounds i32, i32* %out, i64 %idxprom13
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: compute2
>> +; CHECK: PartialAlias: i32* %arrayidx11, i32* %out.addr
>> +define void @compute2(i32 %num, i32* %out.addr) {
>> + %add9 = add i32 %num, 1
>> + %idxprom10 = zext i32 %add9 to i64
>> + %arrayidx11 = getelementptr inbounds i32, i32* %out.addr, i64 %idxprom10
>> + ret void
>> +}
>>
>> Modified: llvm/trunk/test/Analysis/BasicAA/phi-aa.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/phi-aa.ll?rev=246502&r1=246501&r2=246502&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/phi-aa.ll (original)
>> +++ llvm/trunk/test/Analysis/BasicAA/phi-aa.ll Mon Aug 31 17:32:47 2015
>> @@ -39,6 +39,7 @@ return:
>>
>> ; CHECK-LABEL: pr18068
>> ; CHECK: MayAlias: i32* %0, i32* %arrayidx5
>> +; CHECK: NoAlias: i32* %arrayidx13, i32* %arrayidx5
>>
>> define i32 @pr18068(i32* %jj7, i32* %j) {
>> entry:
>>
>> Added: llvm/trunk/test/Analysis/BasicAA/q.bad.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/q.bad.ll?rev=246502&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/q.bad.ll (added)
>> +++ llvm/trunk/test/Analysis/BasicAA/q.bad.ll Mon Aug 31 17:32:47 2015
>> @@ -0,0 +1,180 @@
>> +; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
>> +target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
>> +target triple = "thumbv7--linux-gnueabi"
>> +
>> +; CHECK-LABEL: test_zext_sext_amounts255
>> +; CHECK: NoAlias: i8* %a, i8* %b
>> +define void @test_zext_sext_amounts255(i8* %mem) {
>> + %sext.1 = sext i8 255 to i16
>> + %sext.zext.1 = zext i16 %sext.1 to i64
>> + %sext.2 = sext i8 255 to i32
>> + %sext.zext.2 = zext i32 %sext.2 to i64
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %sext.zext.1
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %sext.zext.2
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: test_zext_sext_amounts
>> +; CHECK: PartialAlias: i8* %a, i8* %b
>> +; %a and %b only PartialAlias as, although they're both zext(sext(%num)) they'll extend the sign by a different
>> +; number of bits before zext-ing the remainder.
>> +define void @test_zext_sext_amounts(i8* %mem, i8 %num) {
>> + %sext.1 = sext i8 %num to i16
>> + %sext.zext.1 = zext i16 %sext.1 to i64
>> + %sext.2 = sext i8 %num to i32
>> + %sext.zext.2 = zext i32 %sext.2 to i64
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %sext.zext.1
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %sext.zext.2
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: based_on_pr18068
>> +; CHECK: NoAlias: i8* %a, i8* %b
>> +; CHECK: NoAlias: i8* %a, i8* %c
>> +define void @based_on_pr18068(i32 %loaded, i8* %mem) {
>> + %loaded.64 = zext i32 %loaded to i64
>> + %add1 = add i32 %loaded, -1 ; unsigned wraps unless %loaded == 0
>> + %add1.64 = zext i32 %add1 to i64 ; is zext(%loaded) always != zext(%loaded - 1)? Yes -> NoAlias
>> + %sub1 = sub i32 %loaded, 1 ; unsigned wraps iff %loaded == 0
>> + %sub1.64 = zext i32 %sub1 to i64 ; is zext(%loaded) always != zext(%loaded - 1)? Yes -> NoAlias
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %loaded.64
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %add1.64
>> + %c = getelementptr inbounds i8, i8* %mem, i64 %sub1.64
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: test_path_dependence
>> +; CHECK: PartialAlias: i8* %a, i8* %b
>> +; CHECK: MustAlias: i8* %a, i8* %c
>> +; CHECK: PartialAlias: i8* %a, i8* %d
>> +define void @test_path_dependence(i32 %p, i8* %mem) {
>> + %p.minus1 = add i32 %p, -1 ; this will always unsigned-wrap, unless %p == 0
>> + %p.minus1.64 = zext i32 %p.minus1 to i64
>> + %p.64.again = add i64 %p.minus1.64, 1 ; either %p (if we wrapped) or 4294967296 (if we didn't)
>> +
>> + %p.nsw.nuw.minus1 = sub nsw nuw i32 %p, 1 ; as nuw we know %p >= 1, and as nsw %p <= 2147483647
>> + %p.nsw.nuw.minus1.64 = zext i32 %p.nsw.nuw.minus1 to i64
>> + %p.nsw.nuw.64.again = add nsw nuw i64 %p.nsw.nuw.minus1.64, 1 ; ...so always exactly %p
>> +
>> + %p.nsw.minus1 = sub nsw i32 %p, 1 ; only nsw, so can only guarantee %p != 0x10000000
>> + %p.nsw.minus1.64 = zext i32 %p.nsw.minus1 to i64 ; when %p > 0x10000000 (ie <= 0 as a signed number) then the zext will make this a huge positive number
>> + %p.nsw.64.again = add nsw i64 %p.nsw.minus1.64, 1 ; ...and so this is very much != %p
>> +
>> + %p.64 = zext i32 %p to i64
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %p.64
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %p.64.again
>> + %c = getelementptr inbounds i8, i8* %mem, i64 %p.nsw.nuw.64.again
>> + %d = getelementptr inbounds i8, i8* %mem, i64 %p.nsw.64.again
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: test_zext_sext_255
>> +; CHECK: NoAlias: i8* %a, i8* %b
>> +define void @test_zext_sext_255(i8* %mem) {
>> + %zext.255 = zext i8 255 to i16 ; 0x00FF
>> + %sext.255 = sext i8 255 to i16 ; 0xFFFF
>> + %zext.sext.255 = zext i16 %sext.255 to i32 ; 0x0000FFFF
>> + %sext.zext.255 = sext i16 %zext.255 to i32 ; 0x000000FF
>> + %zext.zext.sext.255 = zext i32 %zext.sext.255 to i64
>> + %zext.sext.zext.255 = zext i32 %sext.zext.255 to i64
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %zext.zext.sext.255
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %zext.sext.zext.255
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: test_zext_sext_num
>> +; CHECK: PartialAlias: i8* %a, i8* %b
>> +; %a and %b NoAlias if %num == 255 (see @test_zext_sext_255), but %a and %b NoAlias for other values of %num (e.g. 0)
>> +define void @test_zext_sext_num(i8* %mem, i8 %num) {
>> + %zext.num = zext i8 %num to i16
>> + %sext.num = sext i8 %num to i16
>> + %zext.sext.num = zext i16 %sext.num to i32
>> + %sext.zext.num = sext i16 %zext.num to i32
>> + %zext.zext.sext.num = zext i32 %zext.sext.num to i64
>> + %zext.sext.zext.num = zext i32 %sext.zext.num to i64
>> + %a = getelementptr inbounds i8, i8* %mem, i64 %zext.zext.sext.num
>> + %b = getelementptr inbounds i8, i8* %mem, i64 %zext.sext.zext.num
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: uncompressStream
>> +; CHECK: MustAlias: i8* %a, i8* %b
>> +; CHECK: NoAlias: i8* %a, i8* %c
>> +define void @uncompressStream(i8* %mem) {
>> + %zext.255 = zext i8 255 to i32
>> + %sext.255 = sext i8 255 to i32
>> + %a = getelementptr inbounds i8, i8* %mem, i32 255
>> + %b = getelementptr inbounds i8, i8* %mem, i32 %zext.255
>> + %c = getelementptr inbounds i8, i8* %mem, i32 %sext.255
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: constantOffsetHeuristic_i3_i32
>> +; CHECK: NoAlias: i32* %a, i32* %b
>> +; CHECK: NoAlias: i32* %a, i32* %c
>> +; CHECK: NoAlias: i32* %b, i32* %c
>> +define void @constantOffsetHeuristic_i3_i32(i32* %mem, i3 %val) {
>> + %zext.plus.7 = add nsw i3 %val, 7
>> + %zext.plus.4 = add nsw i3 %val, 4
>> + %zext.val = zext i3 %val to i32
>> + %zext.4 = zext i3 %zext.plus.4 to i32
>> + %zext.7 = zext i3 %zext.plus.7 to i32
>> + %a = getelementptr inbounds i32, i32* %mem, i32 %zext.4
>> + %b = getelementptr inbounds i32, i32* %mem, i32 %zext.7
>> + %c = getelementptr inbounds i32, i32* %mem, i32 %zext.val
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: constantOffsetHeuristic_i8_i32
>> +; CHECK: NoAlias: i32* %a, i32* %b
>> +; CHECK: NoAlias: i32* %a, i32* %c
>> +; CHECK: NoAlias: i32* %b, i32* %c
>> +define void @constantOffsetHeuristic_i8_i32(i32* %mem, i8 %val) {
>> + %zext.plus.7 = add nsw i8 %val, 7
>> + %zext.plus.4 = add nsw i8 %val, 4
>> + %zext.val = zext i8 %val to i32
>> + %zext.4 = zext i8 %zext.plus.4 to i32
>> + %zext.7 = zext i8 %zext.plus.7 to i32
>> + %a = getelementptr inbounds i32, i32* %mem, i32 %zext.4
>> + %b = getelementptr inbounds i32, i32* %mem, i32 %zext.7
>> + %c = getelementptr inbounds i32, i32* %mem, i32 %zext.val
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: constantOffsetHeuristic_i3_i8
>> +; CHECK: PartialAlias: i32* %a, i32* %b
>> +; CHECK: NoAlias: i32* %a, i32* %c
>> +; CHECK: PartialAlias: i32* %b, i32* %c
>> +define void @constantOffsetHeuristic_i3_i8(i8* %mem, i3 %val) {
>> + %zext.plus.7 = add nsw i3 %val, 7
>> + %zext.plus.4 = add nsw i3 %val, 4
>> + %zext.val = zext i3 %val to i32
>> + %zext.4 = zext i3 %zext.plus.4 to i32
>> + %zext.7 = zext i3 %zext.plus.7 to i32
>> + %a.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.4
>> + %b.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.7
>> + %c.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.val
>> + %a = bitcast i8* %a.8 to i32*
>> + %b = bitcast i8* %b.8 to i32*
>> + %c = bitcast i8* %c.8 to i32*
>> + ret void
>> +}
>> +
>> +; CHECK-LABEL: constantOffsetHeuristic_i8_i8
>> +; CHECK: PartialAlias: i32* %a, i32* %b
>> +; CHECK: NoAlias: i32* %a, i32* %c
>> +; CHECK: NoAlias: i32* %b, i32* %c
>> +define void @constantOffsetHeuristic_i8_i8(i8* %mem, i8 %val) {
>> + %zext.plus.7 = add nsw i8 %val, 7
>> + %zext.plus.4 = add nsw i8 %val, 4
>> + %zext.val = zext i8 %val to i32
>> + %zext.4 = zext i8 %zext.plus.4 to i32
>> + %zext.7 = zext i8 %zext.plus.7 to i32
>> + %a.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.4
>> + %b.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.7
>> + %c.8 = getelementptr inbounds i8, i8* %mem, i32 %zext.val
>> + %a = bitcast i8* %a.8 to i32*
>> + %b = bitcast i8* %b.8 to i32*
>> + %c = bitcast i8* %c.8 to i32*
>> + ret void
>> +}
>>
>> Copied: llvm/trunk/test/Analysis/BasicAA/zext.ll (from r245393, llvm/trunk/test/Analysis/BasicAA/zext.ll)
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/zext.ll?p2=llvm/trunk/test/Analysis/BasicAA/zext.ll&p1=llvm/trunk/test/Analysis/BasicAA/zext.ll&r1=245393&r2=246502&rev=246502&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Analysis/BasicAA/zext.ll (original)
>> +++ llvm/trunk/test/Analysis/BasicAA/zext.ll Mon Aug 31 17:32:47 2015
>> @@ -205,5 +205,27 @@ define void @test_const_eval_scaled(i8*
>> ret void
>> }
>>
>> +; CHECK-LABEL: Function: foo
>> +; CHECK: MustAlias: float* %arrayidx, float* %arrayidx4.84
>> +define float @foo(i32 *%A, float %rend, float** %wayar) {
>> +entry:
>> + %x0 = load i32, i32* %A, align 4
>> + %conv = sext i32 %x0 to i64
>> + %mul = shl nsw i64 %conv, 3
>> + %call = tail call i8* @malloc(i64 %mul)
>> + %x1 = bitcast i8* %call to float*
>> +
>> + %sub = add nsw i32 %x0, -1
>> + %idxprom = sext i32 %sub to i64
>> + %arrayidx = getelementptr inbounds float, float* %x1, i64 %idxprom
>> + store float %rend, float* %arrayidx, align 8
>> +
>> + %indvars.iv76.83 = add nsw i64 %conv, -1
>> + %arrayidx4.84 = getelementptr inbounds float, float* %x1, i64 %indvars.iv76.83
>> + %x4 = load float, float* %arrayidx4.84, align 8
>> +
>> + ret float %x4
>> +}
>> +
>> ; Function Attrs: nounwind
>> declare noalias i8* @malloc(i64)
>>
>>
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