[llvm] afa192c - [InstCombine] add narrowing transform for low-masked binop with zext operand

[Martin Storsjö via llvm-commits]

On Thu, 9 Jun 2022, Sanjay Patel via llvm-commits wrote:

>
> Author: Sanjay Patel
> Date: 2022-06-09T16:59:26-04:00
> New Revision: afa192cfb6049a15c5542d132d500b910b802c74
>
> URL: https://github.com/llvm/llvm-project/commit/afa192cfb6049a15c5542d132d500b910b802c74
> DIFF: https://github.com/llvm/llvm-project/commit/afa192cfb6049a15c5542d132d500b910b802c74.diff
>
> LOG: [InstCombine] add narrowing transform for low-masked binop with zext operand
>
> https://alive2.llvm.org/ce/z/hRy3rE
>
> As shown in D123408, we can produce this pattern when moving
> cast around, and we already have a related fold for a binop
> with a constant operand.

This commit causes breakage for me - one file which used to compile in 
around a second now hangs (doesn't complete in many minutes at least).

To reproduce, download https://martin.st/temp/remap-preproc.c and try to 
compile it with "clang -target x86_64-w64-mingw32 -w -c -O2 
remap-preproc.c".

// Martin