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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