[Bug target/104271] New: 538.imagick_r run-time at -Ofast -march=native regressed by 26% on Intel Cascade Lake server CPU

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104271

            Bug ID: 104271
           Summary: 538.imagick_r run-time at -Ofast -march=native
                    regressed by 26% on Intel Cascade Lake server CPU
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jamborm at gcc dot gnu.org
                CC: liuhongt at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

On our Intel Cascade Lake server CPU, the benchmark 538.imagick_r from
the SPEC 2017 FPrate suite is 26% slower when built with GCC 12 using
options -Ofast -march=native than when built with GCC 11 with the same
options.

I have bisected the issue to r12-2549-g872da9a6f664a0:

  872da9a6f664a06d73c987aa0cb2e5b830158a10 is the first bad commit
  commit 872da9a6f664a06d73c987aa0cb2e5b830158a10
  Author: liuhongt <hongtao.liu@intel.com>
  Date:   Fri Mar 26 10:56:47 2021 +0800

    Add the member integer_to_sse to processor_cost as a cost simulation for
movd/pinsrd. It will be used to calculate the cost of vec_construct.

    gcc/ChangeLog: 

            PR target/99881
            * config/i386/i386.h (processor_costs): Add new member
            integer_to_sse.
            * config/i386/x86-tune-costs.h (ix86_size_cost, i386_cost,
            i486_cost, pentium_cost, lakemont_cost, pentiumpro_cost,
            geode_cost, k6_cost, athlon_cost, k8_cost, amdfam10_cost,
            bdver_cost, znver1_cost, znver2_cost, znver3_cost,
            btver1_cost, btver2_cost, btver3_cost, pentium4_cost,
            nocona_cost, atom_cost, atom_cost, slm_cost, intel_cost,
            generic_cost, core_cost): Initialize integer_to_sse same value
            as sse_op.
            (skylake_cost): Initialize integer_to_sse twice as much as sse_op.
            * config/i386/i386.c (ix86_builtin_vectorization_cost):
            Use integer_to_sse instead of sse_op to calculate the cost of
            vec_construct.


It is very likely that the problem is a load-to-store-forwarding stall
issue and so related to PR 80689 but the commit makes it either more
frequent or much worse.

Sorry for reporting this so late, unfortunately we do not benchmark
this class of CPUs periodically.  We do not see the problem on any of
the AMD Zens or Intel Kabylake (client) CPUs.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)