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[ConstraintElim] Use nusw flag for GEP decomposition
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Check for nusw instead of inbounds when decomposing GEPs.

In this particular case, we can also look through multiple nusw
flags, because we will ultimately be working in the unsigned
constraint system.
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@nikic
nikic committed Dec 3, 2024
1 parent a7fda0e commit 10223c7
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Showing 2 changed files with 70 additions and 5 deletions.
10 changes: 5 additions & 5 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -387,12 +387,12 @@ struct OffsetResult {
Value *BasePtr;
APInt ConstantOffset;
SmallMapVector<Value *, APInt, 4> VariableOffsets;
bool AllInbounds;
GEPNoWrapFlags NW;

OffsetResult() : BasePtr(nullptr), ConstantOffset(0, uint64_t(0)) {}

OffsetResult(GEPOperator &GEP, const DataLayout &DL)
: BasePtr(GEP.getPointerOperand()), AllInbounds(GEP.isInBounds()) {
: BasePtr(GEP.getPointerOperand()), NW(GEP.getNoWrapFlags()) {
ConstantOffset = APInt(DL.getIndexTypeSizeInBits(BasePtr->getType()), 0);
}
};
Expand Down Expand Up @@ -426,7 +426,7 @@ static OffsetResult collectOffsets(GEPOperator &GEP, const DataLayout &DL) {
Result.ConstantOffset += ConstantOffset2;
if (Result.VariableOffsets.size() == 0 && VariableOffsets2.size() == 1)
Result.VariableOffsets = VariableOffsets2;
Result.AllInbounds &= InnerGEP->isInBounds();
Result.NW &= InnerGEP->getNoWrapFlags();
}
return Result;
}
Expand All @@ -450,9 +450,9 @@ static Decomposition decomposeGEP(GEPOperator &GEP,

assert(!IsSigned && "The logic below only supports decomposition for "
"unsigned predicates at the moment.");
const auto &[BasePtr, ConstantOffset, VariableOffsets, AllInbounds] =
const auto &[BasePtr, ConstantOffset, VariableOffsets, NW] =
collectOffsets(GEP, DL);
if (!BasePtr || !AllInbounds)
if (!BasePtr || !NW.hasNoUnsignedSignedWrap())
return &GEP;

Decomposition Result(ConstantOffset.getSExtValue(), DecompEntry(1, BasePtr));
Expand Down
65 changes: 65 additions & 0 deletions llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -630,3 +630,68 @@ ptr.check:
exit:
ret i4 3
}

define i1 @test_nusw(ptr %p, i32 %x, i32 %y) {
; CHECK-LABEL: @test_nusw(
; CHECK-NEXT: [[X_EXT:%.*]] = zext i32 [[X:%.*]] to i64
; CHECK-NEXT: [[Y_EXT:%.*]] = zext i32 [[Y:%.*]] to i64
; CHECK-NEXT: [[CMP1:%.*]] = icmp ugt i64 [[X_EXT]], [[Y_EXT]]
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP1]])
; CHECK-NEXT: [[GEP_X:%.*]] = getelementptr nusw i8, ptr [[P:%.*]], i64 [[X_EXT]]
; CHECK-NEXT: [[GEP_Y:%.*]] = getelementptr nusw i8, ptr [[P]], i64 [[Y_EXT]]
; CHECK-NEXT: ret i1 true
;
%x.ext = zext i32 %x to i64
%y.ext = zext i32 %y to i64
%cmp1 = icmp ugt i64 %x.ext, %y.ext
call void @llvm.assume(i1 %cmp1)
%gep.x = getelementptr nusw i8, ptr %p, i64 %x.ext
%gep.y = getelementptr nusw i8, ptr %p, i64 %y.ext
%cmp2 = icmp ugt ptr %gep.x, %gep.y
ret i1 %cmp2
}

define i1 @test_nusw_nested(ptr %p, i32 %x, i32 %y) {
; CHECK-LABEL: @test_nusw_nested(
; CHECK-NEXT: [[X_EXT:%.*]] = zext i32 [[X:%.*]] to i64
; CHECK-NEXT: [[Y_EXT:%.*]] = zext i32 [[Y:%.*]] to i64
; CHECK-NEXT: [[CMP1:%.*]] = icmp ugt i64 [[X_EXT]], [[Y_EXT]]
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP1]])
; CHECK-NEXT: [[GEP_X:%.*]] = getelementptr nusw i8, ptr [[P:%.*]], i64 [[X_EXT]]
; CHECK-NEXT: [[GEP_X1:%.*]] = getelementptr nusw i8, ptr [[GEP_X]], i64 1
; CHECK-NEXT: [[GEP_Y:%.*]] = getelementptr nusw i8, ptr [[P]], i64 [[Y_EXT]]
; CHECK-NEXT: ret i1 true
;
%x.ext = zext i32 %x to i64
%y.ext = zext i32 %y to i64
%cmp1 = icmp ugt i64 %x.ext, %y.ext
call void @llvm.assume(i1 %cmp1)
%gep.x = getelementptr nusw i8, ptr %p, i64 %x.ext
%gep.x1 = getelementptr nusw i8, ptr %gep.x, i64 1
%gep.y = getelementptr nusw i8, ptr %p, i64 %y.ext
%cmp2 = icmp ugt ptr %gep.x1, %gep.y
ret i1 %cmp2
}

define i1 @test_missing_nusw(ptr %p, i32 %x, i32 %y) {
; CHECK-LABEL: @test_missing_nusw(
; CHECK-NEXT: [[X_EXT:%.*]] = zext i32 [[X:%.*]] to i64
; CHECK-NEXT: [[Y_EXT:%.*]] = zext i32 [[Y:%.*]] to i64
; CHECK-NEXT: [[CMP1:%.*]] = icmp ugt i64 [[X_EXT]], [[Y_EXT]]
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP1]])
; CHECK-NEXT: [[GEP_X:%.*]] = getelementptr nusw i8, ptr [[P:%.*]], i64 [[X_EXT]]
; CHECK-NEXT: [[GEP_X1:%.*]] = getelementptr i8, ptr [[GEP_X]], i64 1
; CHECK-NEXT: [[GEP_Y:%.*]] = getelementptr nusw i8, ptr [[P]], i64 [[Y_EXT]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp ugt ptr [[GEP_X1]], [[GEP_Y]]
; CHECK-NEXT: ret i1 [[CMP2]]
;
%x.ext = zext i32 %x to i64
%y.ext = zext i32 %y to i64
%cmp1 = icmp ugt i64 %x.ext, %y.ext
call void @llvm.assume(i1 %cmp1)
%gep.x = getelementptr nusw i8, ptr %p, i64 %x.ext
%gep.x1 = getelementptr i8, ptr %gep.x, i64 1
%gep.y = getelementptr nusw i8, ptr %p, i64 %y.ext
%cmp2 = icmp ugt ptr %gep.x1, %gep.y
ret i1 %cmp2
}

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