[llvm] r236894 - [BasicAA] Fix zext & sext handling
Sanjoy Das
sanjoy at playingwithpointers.com
Fri May 8 11:58:56 PDT 2015
Author: sanjoy
Date: Fri May 8 13:58:55 2015
New Revision: 236894
URL: http://llvm.org/viewvc/llvm-project?rev=236894&view=rev
Log:
[BasicAA] Fix zext & sext handling
Summary:
There are several unhandled edge cases in BasicAA's GetLinearExpression
method. This changes fixes outstanding issues, including zext / sext of
a constant with the sign bit set, and the refusal to decompose zexts or
sexts of wrapping arithmetic.
Test Plan: Unit tests added in //q.ext.ll//.
Patch by Nick White.
Reviewers: hfinkel, sanjoy
Reviewed By: hfinkel, sanjoy
Subscribers: sanjoy, llvm-commits, hfinkel
Differential Revision: http://reviews.llvm.org/D6682
Added:
llvm/trunk/test/Analysis/BasicAA/q.bad.ll
Modified:
llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=236894&r1=236893&r2=236894&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Fri May 8 13:58:55 2015
@@ -162,20 +162,26 @@ static bool isObjectSize(const Value *V,
//===----------------------------------------------------------------------===//
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;
- 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 {
@@ -193,10 +199,12 @@ namespace {
///
/// Note that this looks through extends, so the high bits may not be
/// represented in the result.
-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) {
assert(V->getType()->isIntegerTy() && "Not an integer value");
// Limit our recursion depth.
@@ -206,18 +214,32 @@ static Value *GetLinearExpression(Value
return V;
}
- 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();
+ 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 (BinaryOperator *BOp = dyn_cast<BinaryOperator>(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;
+ 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.
@@ -226,45 +248,88 @@ static Value *GetLinearExpression(Value
break;
// 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);
-
- // 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);
+ 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;
}
@@ -346,7 +411,7 @@ DecomposeGEPExpression(const Value *V, i
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.
@@ -358,25 +423,27 @@ DecomposeGEPExpression(const Value *V, i
}
// 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();
continue;
}
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.
@@ -388,8 +455,8 @@ DecomposeGEPExpression(const Value *V, i
// 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;
@@ -398,13 +465,13 @@ DecomposeGEPExpression(const Value *V, i
// 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);
}
@@ -538,6 +605,20 @@ 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
@@ -976,6 +1057,60 @@ aliasSameBasePointerGEPs(const GEPOperat
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),
@@ -1198,7 +1333,7 @@ BasicAliasAnalysis::aliasGEP(const GEPOp
// Zero-extension widens the variable, and so forces the sign
// bit to zero.
- bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt;
+ bool IsZExt = GEP1VariableIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
SignKnownZero |= IsZExt;
SignKnownOne &= !IsZExt;
@@ -1227,6 +1362,10 @@ BasicAliasAnalysis::aliasGEP(const GEPOp
// 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
@@ -1566,14 +1705,14 @@ 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
@@ -1588,7 +1727,7 @@ 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);
}
}
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=236894&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/BasicAA/q.bad.ll (added)
+++ llvm/trunk/test/Analysis/BasicAA/q.bad.ll Fri May 8 13:58:55 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
+}
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