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[InstCombine] Prevent infinite loop with two shifts #118806

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Merged
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Dec 5, 2024
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[InstCombine] Prevent infinite loop with two shifts #118806

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3 changes: 2 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -427,7 +427,8 @@ Instruction *InstCombinerImpl::commonShiftTransforms(BinaryOperator &I) {
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;

if (Constant *CUI = dyn_cast<Constant>(Op1))
Constant *CUI;
if (match(Op1, m_ImmConstant(CUI)))
if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
return Res;

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16 changes: 16 additions & 0 deletions llvm/test/Transforms/InstCombine/shl-twice-constant.ll
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@nikic nikic Dec 5, 2024

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The last two instructions in this test shouldn't be needed, it can be reduced to:

@c = external constant i8
@c2 = external constant i8

define i64 @testfunc() {
  %shl1 = shl i64 1, ptrtoint (ptr @c2 to i64)
  %shl2 = shl i64 %shl1, ptrtoint (ptr @c to i64)
  ret i64 %shl2
}
```.

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@momo5502 momo5502 Dec 5, 2024

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test adjusted. thank you for the review :)

Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

@c = external constant i8
@c2 = external constant i8

define i64 @testfunc() {
; CHECK-LABEL: @testfunc(
; CHECK-NEXT: [[SHL1:%.*]] = shl nuw i64 1, ptrtoint (ptr @c2 to i64)
; CHECK-NEXT: [[SHL2:%.*]] = shl i64 [[SHL1]], ptrtoint (ptr @c to i64)
; CHECK-NEXT: ret i64 [[SHL2]]
;
%shl1 = shl i64 1, ptrtoint (ptr @c2 to i64)
%shl2 = shl i64 %shl1, ptrtoint (ptr @c to i64)
ret i64 %shl2
}
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