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#78023 is revert #78024

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vitalybuka opened this issue Jan 13, 2024 · 2 comments
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#78023 is revert #78024

vitalybuka opened this issue Jan 13, 2024 · 2 comments
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@dtcxzyw
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llvm:instcombine miscompilation

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@vitalybuka
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Breaking https://lab.llvm.org/buildbot/#/builders/236/builds/8673
@vitalybuka vitalybuka mentioned this issue Jan 13, 2024
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@vitalybuka
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I believe the issue is that truncation will change results e.g. here
A1 = 0xff000000
A2 = 0xff00000000

define i1 @test4_icmp_with_var_mismatched_type(i32 %A1, i64 %A2) {
; CHECK-LABEL: @test4_icmp_with_var_mismatched_type(
; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[A2:%.*]] to i32
; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[TMP1]], [[A1:%.*]]
; CHECK-NEXT:    ret i1 [[C]]
;
  %B1 = inttoptr i32 %A1 to ptr
  %B2 = inttoptr i64 %A2 to ptr
  %C = icmp ugt ptr %B1, %B2
  ret i1 %C
}

@dtcxzyw
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dtcxzyw commented Jan 13, 2024

I believe the issue is that truncation will change results e.g. here A1 = 0xff000000 A2 = 0xff00000000

define i1 @test4_icmp_with_var_mismatched_type(i32 %A1, i64 %A2) {
; CHECK-LABEL: @test4_icmp_with_var_mismatched_type(
; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[A2:%.*]] to i32
; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[TMP1]], [[A1:%.*]]
; CHECK-NEXT:    ret i1 [[C]]
;
  %B1 = inttoptr i32 %A1 to ptr
  %B2 = inttoptr i64 %A2 to ptr
  %C = icmp ugt ptr %B1, %B2
  ret i1 %C
}

It is correct because the bit width of pointer is 32 in the test...

vitalybuka added a commit that referenced this issue Jan 13, 2024
@vitalybuka
Revert "[InstCombine] Fold `icmp pred (inttoptr X), (inttoptr Y) -> i…
253d2f9 
…cmp pred X, Y`" (#78023)

Reverts #77832

To fix https://lab.llvm.org/buildbot/#/builders/236/builds/8673

Also truncation to shorter type looks incorrect.

Issue for tracking #78024 .
@dtcxzyw dtcxzyw closed this as completed Jan 14, 2024
justinfargnoli pushed a commit to justinfargnoli/llvm-project that referenced this issue Jan 28, 2024
@vitalybuka @justinfargnoli
Revert "[InstCombine] Fold `icmp pred (inttoptr X), (inttoptr Y) -> i…
c2216a5 
…cmp pred X, Y`" (llvm#78023)

Reverts llvm#77832

To fix https://lab.llvm.org/buildbot/#/builders/236/builds/8673

Also truncation to shorter type looks incorrect.

Issue for tracking llvm#78024 .
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