On Thu, Jun 20, 2013 at 2:52 PM, Jeff Law <l...@redhat.com> wrote:
> On 06/20/2013 04:49 AM, Andreas Schwab wrote:
>>
>> Jeff Law <l...@redhat.com> writes:
>>
>>> +/* { dg-final { scan-tree-dump-times "Replaced" 8 "forwprop1"} } */
>>
>>
>> $ grep -c Replaced forwprop-28.c.022t.forwprop1
>> 16
>>
>> ;; Function test (test, funcdef_no=0, decl_uid=1388, symbol_order=0)
>>
>> Replaced 'rotate_7 == 0' with '_6 == 0'
>> Replaced '_6 == 0' with 'code_5(D) != 22'
>
> Target?
>
> Give me enough information and I'll gladly take a look. Give me junk and
> I'll ignore.
I see this now as well with match-and-simplify and a pending merge piece
(soon to be committed, with testcase adjustment). We have a conflicting
transform, so if you for example consider
void
test_4 (int code)
{
char *temp = frob ();
int rotate = (code == 22);
if (temp == 0 || !rotate)
oof ();
}
then the conflicting transform is to simplify !(code == 22) to code != 22.
If that happens first then the if () no longer is of X || !Y form but we
see X || Y and thus your transform no longer applies (the transform
meanwhile moved to match.pd - I am now moving !(code == 22) to
code != 22 as well).
Btw, I see better generated code on x86 when doing !(code == 22)
-> code != 22 rather than transforming temp == 0 || !rotate to
rotate <= (temp == 0). With your transform I see
movl %edi, %ebx
call frob
cmpl $22, %ebx
sete %dl
testq %rax, %rax
sete %al
cmpb %al, %dl
jbe .L17
while with the code != 22 one I see
movl %edi, %ebx
call frob
testq %rax, %rax
je .L28
cmpl $22, %ebx
jne .L28
So I wonder if it is beneficial at all ...
Thanks,
Richard.
> jeff
