[Bug rtl-optimization/31396] Inline code performance much worse than out-of-line

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #7 from ubizjak at gmail dot com  2007-04-04 08:05 -------
This is the minimal test case for this bug:

--cut here--
extern void foo(void);

double *data;

double test()
{
  double sum = 123.321;
  int i;

  for (i=0; i<4; i++)
    sum += data[i];

  foo();
  foo();

  return sum;
}
--cut here--

Without the second call to foo(), function compiles to (gcc version 4.3.0
20070403 (experimental)):

test:
        subq    $24, %rsp
        movq    data(%rip), %rdx
        movl    $1, %eax
        movsd   .LC0(%rip), %xmm0
        addsd   (%rdx), %xmm0
.L2:
        addsd   (%rdx,%rax,8), %xmm0
        addq    $1, %rax
        cmpq    $4, %rax
        jne     .L2

        movsd   %xmm0, (%rsp)
        call    foo
        movsd   (%rsp), %xmm0
        addq    $24, %rsp
        ret

When the second call to foo() is added, RA gets confused and pushes
sum variable to stack:

test:
        subq    $8, %rsp
        movq    data(%rip), %rdx
        movl    $1, %eax
        movsd   .LC0(%rip), %xmm0
        addsd   (%rdx), %xmm0
        movsd   %xmm0, (%rsp)          <= here
.L2:
        movsd   (%rsp), %xmm0          <= here
        addsd   (%rdx,%rax,8), %xmm0
        addq    $1, %rax
        cmpq    $4, %rax
        movsd   %xmm0, (%rsp)          <= here
        jne     .L2

        call    foo
        call    foo
        movsd   (%rsp), %xmm0
        addq    $8, %rsp
        ret


-- 

ubizjak at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ubizjak at gmail dot com
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
      Known to fail|                            |4.3.0
   Last reconfirmed|0000-00-00 00:00:00         |2007-04-04 08:05:01
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31396