[llvm-bugs] [Bug 41035] Linux kernel build: Regression due memcmp to bcmp optimization

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41035

Nick Desaulniers <ndesaulniers at google.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|REOPENED                    |RESOLVED

--- Comment #28 from Nick Desaulniers <ndesaulniers at google.com> ---
The fix for this is on the kernel side is now in mainline (I expect LTS
backports this week).
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5f074f3e192f10c9fade898b9b3b8812e3d83342

Next time a "compiler optimization" that relies on library support is written,
please ensure that relevant libraries for environments that use LLVM actually
have the proper support.  Otherwise such "compiler optimizations" will regress
builds for environments that don't have the library support.

Specifically in this case, I think it would have been better to ship the
optimized version in glibc first thus proving why such a compiler optimization
would be worthwhile, then verify that all relevant targets support bcmp, then
ship the optimization in LLVM.

Closing this issue now as fixed (it was originally filed because of the kernel
regression).  Please reopen if there's more to do here.

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