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[ConstraintElim] Add support for decomposing gep nuw #118639

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Merged
merged 1 commit into from
Dec 4, 2024
Merged

[ConstraintElim] Add support for decomposing gep nuw #118639

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16 changes: 10 additions & 6 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -452,7 +452,9 @@ static Decomposition decomposeGEP(GEPOperator &GEP,
"unsigned predicates at the moment.");
const auto &[BasePtr, ConstantOffset, VariableOffsets, NW] =
collectOffsets(GEP, DL);
if (!BasePtr || !NW.hasNoUnsignedSignedWrap())
// We support either plain gep nuw, or gep nusw with non-negative offset,
// which implies gep nuw.
if (!BasePtr || NW == GEPNoWrapFlags::none())
return &GEP;

Decomposition Result(ConstantOffset.getSExtValue(), DecompEntry(1, BasePtr));
Expand All @@ -461,11 +463,13 @@ static Decomposition decomposeGEP(GEPOperator &GEP,
IdxResult.mul(Scale.getSExtValue());
Result.add(IdxResult);

// If Op0 is signed non-negative, the GEP is increasing monotonically and
// can be de-composed.
if (!isKnownNonNegative(Index, DL))
Preconditions.emplace_back(CmpInst::ICMP_SGE, Index,
ConstantInt::get(Index->getType(), 0));
if (!NW.hasNoUnsignedWrap()) {
// Try to prove nuw from nusw and nneg.
assert(NW.hasNoUnsignedSignedWrap() && "Must have nusw flag");
if (!isKnownNonNegative(Index, DL))
Preconditions.emplace_back(CmpInst::ICMP_SGE, Index,
ConstantInt::get(Index->getType(), 0));
}
}
return Result;
}
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6 changes: 2 additions & 4 deletions llvm/test/Transforms/ConstraintElimination/gep-arithmetic.ll
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Expand Up @@ -702,8 +702,7 @@ define i1 @test_nuw(ptr %p, i64 %x, i64 %y) {
; CHECK-NEXT: call void @llvm.assume(i1 [[CMP1]])
; CHECK-NEXT: [[GEP_X:%.*]] = getelementptr nuw i8, ptr [[P:%.*]], i64 [[X]]
; CHECK-NEXT: [[GEP_Y:%.*]] = getelementptr nuw i8, ptr [[P]], i64 [[Y]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp ugt ptr [[GEP_X]], [[GEP_Y]]
; CHECK-NEXT: ret i1 [[CMP2]]
; CHECK-NEXT: ret i1 true
;
%cmp1 = icmp ugt i64 %x, %y
call void @llvm.assume(i1 %cmp1)
Expand All @@ -720,8 +719,7 @@ define i1 @test_nuw_nested(ptr %p, i64 %x, i64 %y) {
; CHECK-NEXT: [[GEP_X:%.*]] = getelementptr nuw i8, ptr [[P:%.*]], i64 [[X]]
; CHECK-NEXT: [[GEP_X1:%.*]] = getelementptr nuw i8, ptr [[GEP_X]], i64 1
; CHECK-NEXT: [[GEP_Y:%.*]] = getelementptr nuw i8, ptr [[P]], i64 [[Y]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp ugt ptr [[GEP_X1]], [[GEP_Y]]
; CHECK-NEXT: ret i1 [[CMP2]]
; CHECK-NEXT: ret i1 true
;
%cmp1 = icmp ugt i64 %x, %y
call void @llvm.assume(i1 %cmp1)
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