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loop vectorizer causes dominance violation #30090

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llvmbot opened this issue Oct 20, 2016 · 3 comments
Closed

loop vectorizer causes dominance violation #30090

llvmbot opened this issue Oct 20, 2016 · 3 comments
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bugzilla Issues migrated from bugzilla loopoptim

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@llvmbot
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llvmbot commented Oct 20, 2016

Bugzilla Link 30742
Resolution FIXED
Resolved on Jan 09, 2017 14:10
Version trunk
OS Linux
Attachments -loop-vectorize bug
Reporter LLVM Bugzilla Contributor
CC @Delena,@hfinkel,@ZviRackover

Extended Description

The attached program shows a failure in opt's loop vectorizer pass. I believe this failure has been present for several releases, and I have replicated it with trunk, 3.9, etc.

% opt bug.bc -verify -disable-output
% opt bug.bc -loop-vectorize -disable-output
Instruction does not dominate all uses!
%49 = select i1 %48, i32 1, i32 %47
%43 = add i32 %49, -7
LLVM ERROR: Broken function found, compilation aborted!
@llvmbot
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llvmbot commented Oct 26, 2016

I believe the vectorizer must not be keeping the dominator tree up to date properly. It looks like a SCEVExpander is generating code in an unexpected place.

@llvmbot
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llvmbot commented Jan 3, 2017

Patch submitted here: https://reviews.llvm.org/D28168

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llvmbot commented Jan 9, 2017

Fix committed in r291462. The patch delays the fix-up operation for external induction variable users until after the dominator tree has been updated. But we should work towards keeping the dominator tree up-to-date throughout the transformation, rather than updating it at the end.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 10, 2021
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