[Bug target/87627] New: GCC generates rube-goldberg machine for trivial tail call on 32-bit x86

[bugdal at aerifal dot cx]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87627

            Bug ID: 87627
           Summary: GCC generates rube-goldberg machine for trivial tail
                    call on 32-bit x86
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugdal at aerifal dot cx
  Target Milestone: ---

Simple test case:

extern void bar();
extern void bah(int, int, int);
void foo(int a, int b, int c)
{
    bar();
    bah(a, b, c);
}

Expected output:

  subl $12, %esp
  call bar
  addl $12, %esp
  jmp bah

Actual:

  pushl %edi
  pushl %esi
  pushl %ebx
  movl 16(%esp), %ebx
  movl 20(%esp), %esi
  movl 24(%esp), %edi
  call bar
  movl %edi, 24(%esp)
  movl %esi, 20(%esp)
  movl %ebx, 16(%esp)
  popl %ebx
  popl %esi
  popl %edi
  jmp bah

I'm not clear on whether GCC is unaware that the argument space belongs to the
callee and is preserved across calls, or whether it somehow thinks using
call-saved registers is more optimal in typical cases and is missing the
trivial reason why it's not here.