[PATCH] D125504: [AArch64] Add `foldCSELOfCSEl` DAG combine

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo added a comment.

In D125504#3728916 <https://reviews.llvm.org/D125504#3728916>, @Kmeakin wrote:

> In D125504#3728198 <https://reviews.llvm.org/D125504#3728198>, @mstorsjo wrote:
>
>> I also ran into a case where this commit broke things. One of the miscompiled files is https://martin.st/temp/bprint-preproc.c, compiled with `clang -target aarch64-linux-gnu bprint-preproc.c -O3`, if that helps identifying what the issue is.
>
> Could you elaborate on what broke? What output were you expecting, and how did it change after this patch?

I didn't dive into it in detail to see what actually behaves differently. But it's fairly straightforward to repro it on aarch64-linux like this:

  $ git clone git://source.ffmpeg.org/ffmpeg
  $ cd ffmpeg
  # Build everything with a good clang, run tests which succeed:
  $ ./configure --samples=../samples --cc=clang
  $ make fate-rsync
  $ make -j$(nproc) fate-fits-demux # succeeds
  # Update clang in $PATH to one with this patch applied.
  # Rebuild libavutil/bprint.o:
  $ rm libavutil/bprint.o 
  $ make V=1 -j$(nproc) fate-fits-demux # fails (with a segfault)


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