[PATCH] D136675: [MachineCSE] Allow PRE of instructions that read physical registers

Wed Mar 22 10:37:31 PDT 2023

vigneshv added a comment.

Hi @john.brawn

This change is causing miscompilations in armv7. I was looking into a chromium bug [1] and eventually figured out that it was a regression caused by a clang update in the chromium tree.

I bisected further within the llvm changes and it bisects to this change. If i manually revert this change at current tip-of-tree, the code compiles correctly and works as expected.

Steps to reproduce:

1. build libyuv with "-march=armv7-a -mfloat-abi=softfp -mfpu=neon -O2 -mthumb"
2. Build the attached code snippet from [2] with "-march=armv7-a -mfloat-abi=softfp -mfpu=neon -O2  -mthumb -lyuv"
3. The resulting binary is doing some of the computations incorrectly after this change. If i revert this change, it works as expected.

Please let me know if you need any more details. :)

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=1424089
[2] https://gist.github.com/vigneshvg/09c8414b94187349429641171475ce47

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136675/new/

https://reviews.llvm.org/D136675