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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