bug in DSE?

[Richard Biener]

On February 13, 2021 12:20:48 AM GMT+01:00, Marc Glisse <marc.glisse@inria.fr> wrote:
>On Fri, 12 Feb 2021, Andrew MacLeod via Gcc wrote:
>
>> I dont't want to immediately open a PR,  so I'll just ask about 
>> testsuite/gcc.dg/pr83609.c.
>>
>> the compilation string  is
>>   -O2 -fno-tree-forwprop -fno-tree-ccp -fno-tree-fre -fno-tree-pre 
>> -fno-code-hoisting
>>
>> Which passes as is.
>>
>> if I however add   -fno-tree-vrp   as well, then it looks like dead
>store 
>> maybe does something wong...
>>
>> with EVRP running, we translate function foo() from
>>
>>
>> complex float foo ()
>> {
>>   complex float c;
>>   complex float * c.0_1;
>>   complex float _4;
>>
>>   <bb 2> :
>>   c.0_1 = &c;
>>   MEM[(long long unsigned int *)c.0_1] = 1311768467463790320;
>>   _4 = c;
>
>Isn't that a clear violation of strict aliasing?

Yes. We try DWIM if we see the must-alias though. Please see what the testcase was added for and eventually consider adding -fno-strict-aliasing.