[Bug target/85491] New: [8 Regression] scimark LU Decomposition test 15% slower than GCC 7, 30% slower than peak

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85491

            Bug ID: 85491
           Summary: [8 Regression] scimark LU Decomposition test 15%
                    slower than GCC 7, 30% slower than peak
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

https://gcc.opensuse.org/gcc-old/c++bench-czerny/nbench/ shows a LU
decomposition
slowdown between r257710 and r257760 after a previous improvement between
r253986 and r254023.

These are numbers on Haswell with -O3 -ffast-math -funroll-loops -march=native.

The improvement is likely r253993/r254012, x86 vectorization cost changes.  The
regression might be r257734.