[Bug tree-optimization/34027] [4.3 regression] -Os code size nearly doubled

["rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-11-08 21:45 -------
Confirmed.

Also, on 64bit x86_64 we don't see that this computes the modulus, but do

foobar:
.LFB2:  
        movl    $1000000000, %esi
        movq    %rdi, %rax
        xorl    %edx, %edx
        divq    %rsi
        imulq   $-1000000000, %rax, %rax
        addq    %rdi, %rax
        ret

for

unsigned long long foobar(unsigned long long ns)
{
  return ns % 1000000000L;
}

we produce instead

foobar2:
.LFB3:  
        movl    $1000000000, %edx
        movq    %rdi, %rax
        movq    %rdx, %rcx
        xorl    %edx, %edx
        divq    %rcx
        movq    %rdx, %rax
        ret

which is smaller and faster.  Likewise the 32bit variant:

foobar2:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $8, %esp
        pushl   $0
        pushl   $1000000000
        pushl   12(%ebp)
        pushl   8(%ebp)
        call    __umoddi3
        addl    $16, %esp
        leave
        ret

which would make this argument moot (ok, only by cheating ;)).  The problem
is supposedly that we don't fold

(chrec_apply
  (varying_loop = 1
)
  (chrec = {ns_2(D), +, 0x0ffffffffc4653600}_1)
  (x = ns_2(D) /[fl] 1000000000)
  (res = ns_2(D) + (ns_2(D) /[fl] 1000000000) * 0x0ffffffffc4653600))

which is ns_2 - (ns_2 / 1000000000) * 1000000000.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
  BugsThisDependsOn|                            |32044
             Status|UNCONFIRMED                 |NEW
          Component|c                           |tree-optimization
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2007-11-08 21:45:30
               date|                            |
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34027