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[ValueTracking] Handle assume(trunc x to i1) in ComputeKnownBits #118406

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Merged
merged 1 commit into from
Apr 10, 2025
Merged

[ValueTracking] Handle assume(trunc x to i1) in ComputeKnownBits #118406

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10 changes: 10 additions & 0 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -910,6 +910,16 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
Known.setAllZero();
return;
}
auto *Trunc = dyn_cast<TruncInst>(Arg);
if (Trunc && Trunc->getOperand(0) == V &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
if (Trunc->hasNoUnsignedWrap()) {
Known = KnownBits::makeConstant(APInt(BitWidth, 1));
return;
}
Known.One.setBit(0);
return;
}

// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth == MaxAnalysisRecursionDepth)
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstCombine/assume.ll
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Expand Up @@ -1013,8 +1013,7 @@ define i1 @assume_trunc_nuw_eq_one(i8 %x) {
; CHECK-LABEL: @assume_trunc_nuw_eq_one(
; CHECK-NEXT: [[A:%.*]] = trunc nuw i8 [[X:%.*]] to i1
; CHECK-NEXT: call void @llvm.assume(i1 [[A]])
; CHECK-NEXT: [[Q:%.*]] = icmp eq i8 [[X]], 1
; CHECK-NEXT: ret i1 [[Q]]
; CHECK-NEXT: ret i1 true
;
%a = trunc nuw i8 %x to i1
call void @llvm.assume(i1 %a)
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstSimplify/shr-nop.ll
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Expand Up @@ -385,8 +385,7 @@ define i8 @exact_lshr_lowbit_set_assume_trunc(i8 %x) {
; CHECK-LABEL: @exact_lshr_lowbit_set_assume_trunc(
; CHECK-NEXT: [[COND:%.*]] = trunc i8 [[X:%.*]] to i1
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[SHR:%.*]] = lshr exact i8 [[X]], 1
; CHECK-NEXT: ret i8 [[SHR]]
; CHECK-NEXT: ret i8 [[X]]
;
%cond = trunc i8 %x to i1
call void @llvm.assume(i1 %cond)
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