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opt -jump-threading hangs #47706

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mikaelholmen opened this issue Dec 2, 2020 · 3 comments
Closed

opt -jump-threading hangs #47706

mikaelholmen opened this issue Dec 2, 2020 · 3 comments
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@mikaelholmen
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Bugzilla Link 48362
Resolution FIXED
Resolved on Dec 02, 2020 23:50
Version unspecified
OS Linux
Attachments bbi-50589_reduced.ll reproducer
CC @rotateright
Fixed by commit(s) 9d6d24c

Extended Description

Reproduce with:
opt -o - bbi-50589_reduced.ll -S -jump-threading

It doesn't seem to terminate.

This starts happening after 5486e00:

[InstSimplify] remove poison-unsafe insertelement of undef value

llvm/llvm-project#44826 :
llvm/llvm-project#44826 

SDAG has an identical transform to this, so there's little
chance of any real-world impact. OTOH, that means we are
effectively sweeping the bug out of sight because poison
exists in codegen too.
@rotateright
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In the debugger, this is getting stuck in SimplifyExtractElementInst() -> llvm::findScalarElement().

@rotateright
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I suspect that we could have hit this bug with a less-undef test case even before 5486e00.

I don't know much about jumpthreading, so I put in a lower-level exit in the analysis that was getting tripped up:
https://reviews.llvm.org/rG9d6d24c25056

@mikaelholmen
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Thanks!

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
This issue was closed.
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@rotateright @mikaelholmen