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[LLVM][InstCombine] not (bitcast (cmp A, B) --> bitcast (!cmp A, B) #167693

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Nov 13, 2025
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[LLVM][InstCombine] not (bitcast (cmp A, B) --> bitcast (!cmp A, B) #167693

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0180460
Add tests
paulwalker-arm Nov 12, 2025
468cdd5
[LLVM][InstCombine] not (bitcast (cmp A, B) --> bitcast (!cmp A, B)
paulwalker-arm Nov 12, 2025
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10 changes: 9 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5096,9 +5096,17 @@ Instruction *InstCombinerImpl::foldNot(BinaryOperator &I) {
return &I;
}

// not (bitcast (cmp A, B) --> bitcast (!cmp A, B)
if (match(NotOp, m_OneUse(m_BitCast(m_Value(X)))) &&
match(X, m_OneUse(m_Cmp(Pred, m_Value(), m_Value())))) {
cast<CmpInst>(X)->setPredicate(CmpInst::getInversePredicate(Pred));
return new BitCastInst(X, Ty);
}

// Move a 'not' ahead of casts of a bool to enable logic reduction:
// not (bitcast (sext i1 X)) --> bitcast (sext (not i1 X))
if (match(NotOp, m_OneUse(m_BitCast(m_OneUse(m_SExt(m_Value(X)))))) && X->getType()->isIntOrIntVectorTy(1)) {
if (match(NotOp, m_OneUse(m_BitCast(m_OneUse(m_SExt(m_Value(X)))))) &&
X->getType()->isIntOrIntVectorTy(1)) {
Type *SextTy = cast<BitCastOperator>(NotOp)->getSrcTy();
Value *NotX = Builder.CreateNot(X);
Value *Sext = Builder.CreateSExt(NotX, SextTy);
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78 changes: 78 additions & 0 deletions llvm/test/Transforms/InstCombine/not.ll
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Expand Up @@ -1061,3 +1061,81 @@ if.else:
call void @f2()
unreachable
}

define i8 @invert_bitcasted_icmp(<8 x i32> %a, <8 x i32> %b) {
; CHECK-LABEL: @invert_bitcasted_icmp(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <8 x i32> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: ret i8 [[MASK_AS_INT]]
;
%cmp = icmp sle <8 x i32> %a, %b
%mask.as.int = bitcast <8 x i1> %cmp to i8
%not = xor i8 %mask.as.int, 255
ret i8 %not
}

define i8 @invert_bitcasted_icmp_samesign(<8 x i32> %a, <8 x i32> %b) {
; CHECK-LABEL: @invert_bitcasted_icmp_samesign(
; CHECK-NEXT: [[CMP:%.*]] = icmp samesign sgt <8 x i32> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: ret i8 [[MASK_AS_INT]]
;
%cmp = icmp samesign sle <8 x i32> %a, %b
%mask.as.int = bitcast <8 x i1> %cmp to i8
%not = xor i8 %mask.as.int, 255
ret i8 %not
}

define i8 @invert_bitcasted_icmp_multi_use_1(<8 x i32> %a, <8 x i32> %b) {
; CHECK-LABEL: @invert_bitcasted_icmp_multi_use_1(
; CHECK-NEXT: [[CMP:%.*]] = icmp sle <8 x i32> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: call void (...) @llvm.fake.use(<8 x i1> [[CMP]])
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[MASK_AS_INT]], -1
; CHECK-NEXT: ret i8 [[NOT]]
;
%cmp = icmp sle <8 x i32> %a, %b
call void (...) @llvm.fake.use(<8 x i1> %cmp)
%mask.as.int = bitcast <8 x i1> %cmp to i8
%not = xor i8 %mask.as.int, -1
ret i8 %not
}

define i8 @invert_bitcasted_icmp_multi_use_2(<8 x i32> %a, <8 x i32> %b) {
; CHECK-LABEL: @invert_bitcasted_icmp_multi_use_2(
; CHECK-NEXT: [[CMP:%.*]] = icmp sle <8 x i32> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: call void (...) @llvm.fake.use(i8 [[MASK_AS_INT]])
; CHECK-NEXT: [[NOT:%.*]] = xor i8 [[MASK_AS_INT]], -1
; CHECK-NEXT: ret i8 [[NOT]]
;
%cmp = icmp sle <8 x i32> %a, %b
%mask.as.int = bitcast <8 x i1> %cmp to i8
call void (...) @llvm.fake.use(i8 %mask.as.int)
%not = xor i8 %mask.as.int, -1
ret i8 %not
}

define i8 @invert_bitcasted_fcmp(<8 x float> %a, <8 x float> %b) {
; CHECK-LABEL: @invert_bitcasted_fcmp(
; CHECK-NEXT: [[CMP:%.*]] = fcmp uge <8 x float> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: ret i8 [[MASK_AS_INT]]
;
%cmp = fcmp olt <8 x float> %a, %b
%mask.as.int = bitcast <8 x i1> %cmp to i8
%not = xor i8 %mask.as.int, 255
ret i8 %not
}

define i8 @invert_bitcasted_fcmp_fast(<8 x float> %a, <8 x float> %b) {
; CHECK-LABEL: @invert_bitcasted_fcmp_fast(
; CHECK-NEXT: [[CMP:%.*]] = fcmp fast uge <8 x float> [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MASK_AS_INT:%.*]] = bitcast <8 x i1> [[CMP]] to i8
; CHECK-NEXT: ret i8 [[MASK_AS_INT]]
;
%cmp = fcmp fast olt <8 x float> %a, %b
%mask.as.int = bitcast <8 x i1> %cmp to i8
%not = xor i8 %mask.as.int, 255
ret i8 %not
}
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