[Bug target/99531] New: Performance regression since gcc 9 (argument passing / register allocation)

[stefanrin at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99531

            Bug ID: 99531
           Summary: Performance regression since gcc 9 (argument passing /
                    register allocation)
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: stefanrin at gmail dot com
  Target Milestone: ---
            Target: x86_64

For this source:

int func(int, int, int, int, int, int);
int caller(int a, int b, int c, int d, int e) { return func(0, a, b, c, d, e);
}

the code generated for caller is:

pushq %r12
movl %r8d, %r9d
popq %r12
movl %ecx, %r8d
movl %edx, %ecx
movl %esi, %edx
movl %edi, %esi
xorl %edi, %edi
jmp func

gcc 9 started producing the useless push/pop pair.

Mailing list link:
https://gcc.gnu.org/pipermail/gcc-help/2021-February/139885.html