[Bug target/98303] New: [x86] Bad register allocation when reproducing assembly code

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98303

            Bug ID: 98303
           Summary: [x86] Bad register allocation when reproducing
                    assembly code
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f1(int n)
{
    while (n >= 64)
        n -= 64;

    return n;
}

On x86, with -O3, this generates :

f1(int):
  mov eax, edi
  and eax, 63
  cmp edi, 63
  cmovle eax, edi
  ret

This code :

int f2(int n)
{
    return (n <= 63) ? n : (n & 63);
}

which behaves equivalently, seems to result in poorer generated code :

f2(int):
  mov edx, edi
  mov eax, edi
  and edx, 63
  cmp edi, 63
  cmovg eax, edx
  ret