[NewGVN] Simplification based on metadata/attributes not available on all members of a congruence class causes miscompiles #36888
Comments
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assigned to @fhahn |
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Proposed simple fix https://reviews.llvm.org/D47143 |
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llvm/llvm-bugzilla-archive#37660 covers a related case, where we have Eli also indicated at https://reviews.llvm.org/D47143 that it would be good to fix those issues there too. |
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*** Bug llvm/llvm-bugzilla-archive#37660 has been marked as a duplicate of this bug. *** |
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*** Bug llvm/llvm-bugzilla-archive#38260 has been marked as a duplicate of this bug. *** |
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*** Bug llvm/llvm-bugzilla-archive#38214 has been marked as a duplicate of this bug. *** |
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*** Bug llvm/llvm-bugzilla-archive#38304 has been marked as a duplicate of this bug. *** |
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Thanks Florian for fixing this! |
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mentioned in issue llvm/llvm-bugzilla-archive#37660 |
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mentioned in issue llvm/llvm-bugzilla-archive#38214 |
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mentioned in issue llvm/llvm-bugzilla-archive#38260 |
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mentioned in issue llvm/llvm-bugzilla-archive#38304 |
Extended Description
NewGVN optimizes:
define i1 @test({}** %arg, i1 %arg2) {
br i1 %arg2, label %bb1, label %bb2
bb1:
%load1 = load {}, {}** %arg
%cmp1 = icmp eq {} %load1, null
ret i1 %cmp1
bb2:
%load2 = load {}, {}** %arg, !nonnull !1
%cmp2 = icmp eq {} %load2, null
ret i1 %cmp2
}
!1 = !{}
into:
define i1 @test({}** %arg, i1 %arg2) {
br i1 %arg2, label %bb1, label %bb2
bb1: ; preds = %0
ret i1 false
bb2: ; preds = %0
ret i1 false
}
The reason is that %load1 and %load2 are found congruent with %load2 chosen as leader. Thus %cmp1 in bb1 calls SimplifyCmp with icmp eq {}* %load2, null, which is simplified to i1 false based on the !nonnull metadata of %load2. However, this metadata is not applicable in this branch.
This bug prevents bootstrapping of rustc under newgvn.
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