[llvm] r240787 - [DAGCombine] fold (X >>?, exact C1) << C2 --> X << (C2-C1)

Tobias Grosser tobias at grosser.es
Fri Jun 26 08:27:47 PDT 2015


On 06/26/2015 04:51 PM, Benjamin Kramer wrote:
> Author: d0k
> Date: Fri Jun 26 09:51:36 2015
> New Revision: 240787
>
> URL: http://llvm.org/viewvc/llvm-project?rev=240787&view=rev
> Log:
> [DAGCombine] fold (X >>?,exact C1) << C2 --> X << (C2-C1)
>
> Instcombine also does this but many opportunities only become visible
> after GEPs are lowered.

The Polly bots report a recent miscompile, with this and the following 
commit looking to be the most likely ones to cause this.

http://lab.llvm.org:8011/builders/perf-x86_64-penryn-O3-polly-fast/builds/8707

The plain clang -O3 bot did not reach this state yet, but I will have a 
look at it later today:

http://lab.llvm.org:8011/builders/perf-x86_64-penryn-O3/builds/5315

(It runs 10 iterations and should be finished in about 5 hours. If we 
just want to check for correctness, within one hour the first iteration 
should be done and we can check the logs for a failure).

Best,
Tobias



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