in your particular example, it is good to copy propagate, right?
I am ok with your fix
Sun
On Wed, Nov 30, 2011 at 9:35 AM, Yiran Wang <yiran.w...@gmail.com> wrote:
> Thanks for your comments.
>
> I am not quite clear about the importance of such an optimization. As
> usually MSTORE are lowered from MSTID/memcpy-alike-intrinsics. It looks
> like not very important for C, as the lowering are usually 1-1 mapping and
> not introducing redanduncies.
>
> I need to look some further to figure out what is needed to enable it.
>
> BTW, any comments about the patch itself?
>
> Best Regards,
> Yiran
>
> On Mon, Nov 28, 2011 at 8:43 PM, Sun Chan <sun.c...@gmail.com> wrote:
>
>> Sorry, stupid of me.
>> I understand wopt does not do copy prop of mload to mstore. OTOH, this
>> had been a goal for a long time. Anyway you can make that work?
>> Sun
>>
>> On Tue, Nov 29, 2011 at 12:37 PM, Yiran Wang <yiran.w...@gmail.com>wrote:
>>
>>> Em, I think you are saying that once entered, it would not exit, but the
>>> loop is not entered at the very beginning, as the initial test would fail.
>>>
>>> Regards,
>>> Yiran
>>>
>>>
>>> On Mon, Nov 28, 2011 at 6:15 PM, Sun Chan <sun.c...@gmail.com> wrote:
>>>
>>>> your example should infinite loop. Pls double check before we further
>>>> discuss this
>>>> Sun
>>>>
>>>> On Tue, Nov 29, 2011 at 8:41 AM, Yiran Wang <yiran.w...@gmail.com>wrote:
>>>>
>>>>> Hi All,
>>>>>
>>>>> Could a gatekeeper review this patch?
>>>>>
>>>>> The test case is as following, and the bug is triggered, when
>>>>> compiling it with -O2.
>>>>>
>>>>> #include <string.h>
>>>>>
>>>>> struct x{
>>>>> int y;
>>>>> int z;
>>>>> };
>>>>>
>>>>> int foo()
>>>>> {
>>>>> struct x xyz,abc;
>>>>> int i;
>>>>> memset(&xyz,0,sizeof(xyz));
>>>>> i = 1;
>>>>> while( i < 0 )
>>>>> {
>>>>> abc.y += xyz.z;
>>>>> xyz.z += 1;
>>>>> i+=i;
>>>>> }
>>>>> memcpy(&abc,&xyz,sizeof(xyz));
>>>>> return abc.y ;
>>>>> }
>>>>>
>>>>> The issue is that after WOPT remove the while loop, it renames SSA and
>>>>> connect the MSTORE and MLOAD lowered from memset and memcpy respectively.
>>>>> It would then try to copy propagate
>>>>>
>>>>> LDC 0
>>>>> LDA ...
>>>>> LDC 8
>>>>> MSTORE
>>>>>
>>>>> to
>>>>>
>>>>> LDA ...
>>>>> LDC 8
>>>>> MLOAD
>>>>>
>>>>> And, it fails to make a CVT op of type I4 and M.
>>>>>
>>>>> As WOPT is not doing copy propagation for MLOAD, so we just abandon
>>>>> the opportunity as a fix.
>>>>> It should be noted that, the DEF is passing the "Propagatable" test,
>>>>> as it is LDC I4, while usual DEF of an MLOAD would be MLOAD.
>>>>>
>>>>> The patch is as following:
>>>>> Index: opt_prop.cxx
>>>>> ===================================================================
>>>>> --- opt_prop.cxx (revision 3827)
>>>>> +++ opt_prop.cxx (working copy)
>>>>> @@ -1307,6 +1307,16 @@
>>>>> if (prop == NOT_PROPAGATABLE)
>>>>> return NULL;
>>>>>
>>>>> + // MLOAD may be defined by a MSTORE as following
>>>>> + // LDC 0
>>>>> + // LDA
>>>>> + // LDC
>>>>> + // MSTORE
>>>>> + // The definition would pass Propagatable test, but we are not going
>>>>> + // to propagate it.
>>>>> + if (x->Opr() == OPR_MLOAD)
>>>>> + return NULL;
>>>>> +
>>>>> x->DecUsecnt();
>>>>> if (icopy_phase)
>>>>> Htable()->Inc_inputprops();
>>>>>
>>>>> Best Regards,
>>>>> Yiran
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>
>>>
>>
>
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