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[ConstraintElim] Don't decompose values wider than 64 bits #68803

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Merged
merged 1 commit into from
Oct 16, 2023
Merged

[ConstraintElim] Don't decompose values wider than 64 bits #68803

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16 changes: 13 additions & 3 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -451,6 +451,19 @@ static Decomposition decompose(Value *V,
return ResA;
};

Type *Ty = V->getType()->getScalarType();
if (Ty->isPointerTy() && !IsSigned) {
if (auto *GEP = dyn_cast<GEPOperator>(V))
return decomposeGEP(*GEP, Preconditions, IsSigned, DL);
return V;
}

// Don't handle integers > 64 bit. Our coefficients are 64-bit large, so
// coefficient add/mul may wrap, while the operation in the full bit width
// would not.
if (!Ty->isIntegerTy() || Ty->getIntegerBitWidth() > 64)
return V;

// Decompose \p V used with a signed predicate.
if (IsSigned) {
if (auto *CI = dyn_cast<ConstantInt>(V)) {
Expand Down Expand Up @@ -478,9 +491,6 @@ static Decomposition decompose(Value *V,
return int64_t(CI->getZExtValue());
}

if (auto *GEP = dyn_cast<GEPOperator>(V))
return decomposeGEP(*GEP, Preconditions, IsSigned, DL);

Value *Op0;
bool IsKnownNonNegative = false;
if (match(V, m_ZExt(m_Value(Op0)))) {
Expand Down
8 changes: 5 additions & 3 deletions llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll
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Expand Up @@ -96,6 +96,7 @@ else:
ret i1 false
}

; TODO: This could be folded.
define i1 @sub_decomp_i80(i80 %a) {
; CHECK-LABEL: @sub_decomp_i80(
; CHECK-NEXT: entry:
Expand All @@ -104,7 +105,8 @@ define i1 @sub_decomp_i80(i80 %a) {
; CHECK-NEXT: br i1 [[C]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: [[SUB_1:%.*]] = sub nuw i80 [[A]], 1973801615886922022913
; CHECK-NEXT: ret i1 true
; CHECK-NEXT: [[C_1:%.*]] = icmp ult i80 [[SUB_1]], 1346612317380797267967
; CHECK-NEXT: ret i1 [[C_1]]
; CHECK: else:
; CHECK-NEXT: ret i1 false
;
Expand Down Expand Up @@ -418,12 +420,12 @@ entry:
ret i1 %res
}

; FIXME: This is a miscompile.
define i1 @pr68751(i128 %arg) {
; CHECK-LABEL: @pr68751(
; CHECK-NEXT: [[SHL1:%.*]] = shl nuw nsw i128 [[ARG:%.*]], 32
; CHECK-NEXT: [[SHL2:%.*]] = shl nuw nsw i128 [[SHL1]], 32
; CHECK-NEXT: ret i1 true
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i128 [[SHL2]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%shl1 = shl nuw nsw i128 %arg, 32
%shl2 = shl nuw nsw i128 %shl1, 32
Expand Down
3 changes: 2 additions & 1 deletion llvm/test/Transforms/ConstraintElimination/shl.ll
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Expand Up @@ -1277,7 +1277,8 @@ define i1 @shl_55() {
; CHECK-LABEL: @shl_55(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SHL_UB:%.*]] = shl nuw nsw i256 1, 55
; CHECK-NEXT: ret i1 true
; CHECK-NEXT: [[SHL_CMP:%.*]] = icmp uge i256 [[SHL_UB]], 1
; CHECK-NEXT: ret i1 [[SHL_CMP]]
;
entry:
%shl.ub = shl nuw nsw i256 1, 55
Expand Down