[llvm-bugs] [Bug 44264] New: m[ft]ppr instruction aliases not implemented

via llvm-bugs llvm-bugs at lists.llvm.org
Tue Dec 10 07:24:06 PST 2019


            Bug ID: 44264
           Summary: m[ft]ppr instruction aliases not implemented
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: colin.samples at gmail.com
                CC: llvm-bugs at lists.llvm.org, nemanja.i.ibm at gmail.com

Created attachment 22924
  --> https://bugs.llvm.org/attachment.cgi?id=22924&action=edit
patch to implement aliases

The mfppr and mtppr instruction aliases are not implemented in LLVM, but they
are in GCC and xlC. m[ft]ppr32 and quite a number of other m[tf]spr aliases are
also not implemented in LLVM.

I stumbled across this when trying to use the `_mm_pause` function
`clang/lib/Headers/ppc_wrappers/xmmintrin.h`, which uses these instructions in
its implementation.

The attached patch adds the instructions. AFAICT, the PPR was introduced in
POWER6, so this patch checks for that, although it seems like a bit much just
to implement an instruction alias.

Another option would be to just change the implementation in `xmmintrin.h` to
use `mfspr Rx,896`. Thoughts?

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