[Bug tree-optimization/82220] New: [8 Regression] SPEC CPU2006 482.sphinx3 ~10% performance regression with trunk@250416

[alexander.nesterovskiy at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82220

            Bug ID: 82220
           Summary: [8 Regression] SPEC CPU2006 482.sphinx3 ~10%
                    performance regression with trunk@250416
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alexander.nesterovskiy at intel dot com
  Target Milestone: ---

Calculation of a min_profitable_iters threshold was changed in r250416
In 482.sphinx3 a wrong path is chosen in a hottest loop which leads to ~45%
performance drop for a particular loop and ~10% performance drop for a whole
test.

According to perf report:
---
Overhead       Samples    Symbol
trunk@250416 (and up-to-date trunk@252756)
  36.91%    --> 527019    vector_gautbl_eval_logs3
  28.03%        400316    mgau_eval                  
   8.90%        127071    subvq_mgau_shortlist       

trunk@250415
  31.72%        402114    mgau_eval
  29.36%    --> 372126    vector_gautbl_eval_logs3
   9.85%        124815    subvq_mgau_shortlist
---

Compiled with: "-Ofast -funroll-loops -march=core-avx2 -mfpmath=sse"