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release/19.x: [InstCombine] Drop noundef attributes in foldCttzCtlz (#116718) #116865

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Merged
merged 1 commit into from
Dec 2, 2024
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release/19.x: [InstCombine] Drop noundef attributes in foldCttzCtlz (#116718) #116865

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4 changes: 3 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -506,8 +506,10 @@ static Instruction *foldCttzCtlz(IntrinsicInst &II, InstCombinerImpl &IC) {

// If ctlz/cttz is only used as a shift amount, set is_zero_poison to true.
if (II.hasOneUse() && match(Op1, m_Zero()) &&
match(II.user_back(), m_Shift(m_Value(), m_Specific(&II))))
match(II.user_back(), m_Shift(m_Value(), m_Specific(&II)))) {
II.dropUBImplyingAttrsAndMetadata();
return IC.replaceOperand(II, 1, IC.Builder.getTrue());
}

Constant *C;

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16 changes: 16 additions & 0 deletions llvm/test/Transforms/InstCombine/shift-cttz-ctlz.ll
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Expand Up @@ -15,6 +15,22 @@ entry:
ret i32 %res
}

; Make sure that noundef is dropped.

define i32 @shl_cttz_false_noundef(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_cttz_false_noundef(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CTTZ:%.*]] = call range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[Y]], i1 true)
; CHECK-NEXT: [[RES:%.*]] = shl i32 [[X]], [[CTTZ]]
; CHECK-NEXT: ret i32 [[RES]]
;
entry:
%cttz = call noundef i32 @llvm.cttz.i32(i32 %y, i1 false)
%res = shl i32 %x, %cttz
ret i32 %res
}

define i32 @shl_ctlz_false(i32 %x, i32 %y) {
; CHECK-LABEL: define i32 @shl_ctlz_false(
; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
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