Re: [PATCH] Remove also 2nd argument for unused delete operator (PR tree-optimization/91270).

[Marc Glisse <marc.glisse@inria.fr>]

On Tue, 30 Jul 2019, Martin Liška wrote:

> On 7/30/19 1:35 PM, Marc Glisse wrote:
>> +          /* Some delete operators have size as 2nd argument.  */
>>
>> Some delete operators have 3 arguments. From cp/decl.c:
>>
>>             /* operator delete (void *, size_t, align_val_t); */
>>
>
> Yep, I know. The patch I installed expects at least 2 arguments:
>
> +                 /* Some delete operators have size as 2nd argument.  */
> +                 if (is_delete_operator && gimple_call_num_args (stmt) >= 2)

True, I guess I am a bit confused why the second argument (which could be 
either size or alignment) needs special handling (mark_operand_necessary) 
while the third one does not (it is usually a constant).

I tried to experiment to understand, but it is complicated because 
including <new> disables the optimization:

#include <new>
void fn1() {
     char*p=new char;
     delete p;
}

This ICEs with -O -std=c++17:

int a = 64;
std::align_val_t b{64};
void fn1() {
   void *s = operator new(a,b);
   operator delete(s,8+*(unsigned long*)s,b);
}


-- 
Marc Glisse