[Bug tree-optimization/105314] New: ifcvt regression in noce_try_store_flag_mask

[christophm30 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105314

            Bug ID: 105314
           Summary: ifcvt regression in noce_try_store_flag_mask
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: christophm30 at gmail dot com
  Target Milestone: ---

The function noce_try_store_flag_mask() in ifcvt.cc converts
"if (test) x = 0;" to "x &= -(test == 0);" (if costs permit that).

Commit 3a7ba8fd (which was introduced a month ago to fix PR104960) triggers a
regression so that the if-conversion can't be performed anymore.

On RISC-V this manifests as follows:
"""
long func(long a, long b, long c)
{
  if (c)
    a = 0;
  return a;
}
"""

Old code:
0000000000000000 <func>:
   0:   00163613                seqz    a2,a2
   4:   40c00633                neg     a2,a2
   8:   8d71                    and     a0,a0,a2
   a:   8082                    ret

New (branching) code:
0000000000000000 <func>:
   0:   c211                    beqz    a2,4 <.L1>
   2:   4501                    li      a0,0
0000000000000004 <.L1>:
   4:   8082                    ret

Looking through the test suite, I could only find the file
"gcc.target/arm/ifcvt-size-check.c" which should be affected by this regression
as well. However, I haven't tested that.