[PATCH] D122900: [x86] Disable optimization involved in an infinite loop inside DAG combiner.

[pierre gousseau via Phabricator via llvm-commits]

pgousseau added a subscriber: wristow.
pgousseau added a comment.

In D122900#3422266 <https://reviews.llvm.org/D122900#3422266>, @lebedev.ri wrote:

> Do you know which commit introduced the problem, or which transforms conflict?
> This looks like a pretty heavy hammer.

Thank you Roman for reviewing!
The regression appeared after https://github.com/llvm/llvm-project/commit/8a156d1c2795189389fadbf33702384f522f2506 (thank you @wristow  for finding it)
As @RKSimon  found out, the IR does not get generated anymore from the original C++ test case but the issue is still present.
I am hopeful we can reintroduce the optimization (at a later codegen stage maybe?) but I would like to do some performance analysis first to see if it is still a win.


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