[llvm-bugs] [Bug 42616] New: Regression since "[X86] Add MOVSDrr->MOVLPDrm entry to load folding table. Add custom handling to turn UNPCKLPDrr->MOVHPDrm when load is under aligned."

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42616

            Bug ID: 42616
           Summary: Regression since "[X86] Add MOVSDrr->MOVLPDrm entry to
                    load folding table. Add custom handling to turn
                    UNPCKLPDrr->MOVHPDrm when load is under aligned."
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: martin at martin.st
                CC: craig.topper at gmail.com, hans at chromium.org,
                    llvm-bugs at lists.llvm.org, llvm-dev at redking.me.uk,
                    spatel+llvm at rotateright.com

Created attachment 22243
  --> https://bugs.llvm.org/attachment.cgi?id=22243&action=edit
Reproduction source code

Since SVN r365287, "[X86] Add MOVSDrr->MOVLPDrm entry to load folding table.
Add custom handling to turn UNPCKLPDrr->MOVHPDrm when load is under aligned.",
some code seems to be miscompiled, failing tests.

I haven't yet been able to pinpoint what the issue is, but if building the
libav project (https://git.libav.org/?p=libav.git) for i686-w64-mingw32 with
clang, the mp3 float decoder tests start failing:
https://fate.libav.org/i686-mingw32-clang-trunk

The failure is isolated to one single source file (attached in preprocessed
form); if compiled as "clang -target i686-w64-mingw32 -c -O3
mpegaudiodec_float-preproc.c -o libavcodec/mpegaudiodec_float.o", it fails
tests if built with a compiler past this commit, and succeeds all tests if
built with the older compiler version.

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