[Bug target/46471] Worse register regalloc leads to bigger code at -Os; not using callee saved registers instead use stack locations

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46471

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |4.4.7
            Summary|Worse register regalloc     |Worse register regalloc
                   |leads to bigger code at -Os |leads to bigger code at
                   |                            |-Os; not using callee saved
                   |                            |registers instead use stack
                   |                            |locations
   Last reconfirmed|                            |2025-01-08
             Status|UNCONFIRMED                 |NEW
             Target|                            |x86_64
     Ever confirmed|0                           |1
      Known to fail|                            |15.0, 4.5.3

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Trunk produces:

merged_1v_upsample:
 push   %rbx
 mov    %rdx,%rbx
 sub    $0x10,%rsp
 mov    (%r9),%eax
 mov    (%rdx),%edx
 mov    %r9,0x8(%rsp)
 lea    (%r8,%rax,8),%rcx
 mov    0x260(%rdi),%rax
 call   *0x18(%rax)
 mov    0x8(%rsp),%r9
 incl   (%r9)
 incl   (%rbx)
 add    $0x10,%rsp
 pop    %rbx
 ret

Which is the similar to 4.6/4.5.

So instead of using a stack location, 4.3 would use a callee saved register
which produces smaller code because push is only 1/2 bytes and pop is 1 byte
while saving the stack is 5 bytes and restoring is 5 bytes.