[Bug rtl-optimization/70873] New: [GCC7 Regressio] 20% performance regression at 482.sphinx3 after r235442 with -O2 -m32 on Haswell.

[ysrumyan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70873

            Bug ID: 70873
           Summary: [GCC7 Regressio] 20% performance regression at
                    482.sphinx3 after r235442 with -O2 -m32 on Haswell.
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ysrumyan at gmail dot com
  Target Milestone: ---

This degradation is caused by known issue with partial register dependency:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57954
and can be reproduced with the attached simple test-case:
  before fix
    vxorpd    %xmm4, %xmm4, %xmm4
    vcvtss2sd    (%esi,%eax,4), %xmm4, %xmm4
  after fix
    vxorpd    %xmm6, %xmm6, %xmm6
    vcvtss2sd    (%esi,%eax,4), %xmm6, %xmm7
I assume that register renaming must not split such register live range but
simply consider it as one.