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[InstCombine] Fold trunc nuw/nsw X to i1 -> true IFF X != 0 #119131

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Merged
merged 1 commit into from
Dec 8, 2024
Merged

[InstCombine] Fold trunc nuw/nsw X to i1 -> true IFF X != 0 #119131

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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -934,6 +934,11 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
}
}

if (DestWidth == 1 &&
(Trunc.hasNoUnsignedWrap() || Trunc.hasNoSignedWrap()) &&
isKnownNonZero(Src, SQ.getWithInstruction(&Trunc)))
return replaceInstUsesWith(Trunc, ConstantInt::getTrue(DestTy));

bool Changed = false;
if (!Trunc.hasNoSignedWrap() &&
ComputeMaxSignificantBits(Src, /*Depth=*/0, &Trunc) <= DestWidth) {
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6 changes: 2 additions & 4 deletions llvm/test/Transforms/InstCombine/trunc.ll
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Expand Up @@ -1129,8 +1129,7 @@ define i1 @trunc_nuw_i1_non_zero(i8 %1) {
; CHECK-LABEL: @trunc_nuw_i1_non_zero(
; CHECK-NEXT: [[TMP2:%.*]] = icmp ne i8 [[TMP0:%.*]], 0
; CHECK-NEXT: tail call void @llvm.assume(i1 [[TMP2]])
; CHECK-NEXT: [[RET:%.*]] = trunc nuw i8 [[TMP0]] to i1
; CHECK-NEXT: ret i1 [[RET]]
; CHECK-NEXT: ret i1 true
;
%3 = icmp ne i8 %1, 0
tail call void @llvm.assume(i1 %3)
Expand Down Expand Up @@ -1177,8 +1176,7 @@ define i1 @trunc_nsw_i1_non_zero(i8 %1) {
; CHECK-LABEL: @trunc_nsw_i1_non_zero(
; CHECK-NEXT: [[TMP2:%.*]] = icmp ne i8 [[TMP0:%.*]], 0
; CHECK-NEXT: tail call void @llvm.assume(i1 [[TMP2]])
; CHECK-NEXT: [[RET:%.*]] = trunc nsw i8 [[TMP0]] to i1
; CHECK-NEXT: ret i1 [[RET]]
; CHECK-NEXT: ret i1 true
;
%3 = icmp ne i8 %1, 0
tail call void @llvm.assume(i1 %3)
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