[llvm] r310190 - [X86] Enable isel to use the PAUSE instruction even when SSE2 is disabled

[Hans Wennborg via llvm-commits]

On Sat, Aug 5, 2017 at 4:34 PM, Craig Topper via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: ctopper
> Date: Sat Aug  5 16:34:44 2017
> New Revision: 310190
>
> URL: http://llvm.org/viewvc/llvm-project?rev=310190&view=rev
> Log:
> [X86] Enable isel to use the PAUSE instruction even when SSE2 is disabled
>
> Summary:
> On older processors this instruction encoding is treated as a NOP.
>
> MSVC doesn't disable intrinsics based on features the way clang/gcc does. Because the PAUSE instruction encoding doesn't crash older processors, some software out there uses these intrinsics without checking for SSE2.
>
> This change also seems to also be consistent with gcc behavior.
>
> Fixes PR34079
>
> Reviewers: RKSimon, zvi
>
> Reviewed By: RKSimon
>
> Subscribers: llvm-commits
>
> Differential Revision: https://reviews.llvm.org/D36361

Merged to 5.0 in r310293.