[PATCH] Have HasSideEffects() return false for __attribute__((const)) functions

[Aaron Ballman]

On Mon, Mar 23, 2015 at 12:33 PM, hfinkel at anl.gov <hfinkel at anl.gov> wrote:
> In http://reviews.llvm.org/D8548#145253, @mkuper wrote:
>
>> I think PureAttr isn't strong enough.
>>
>> char foo(char *a)
>>  {
>>
>>   return *a;
>>
>> }
>>
>> is pure, but isn't side-effect free.
>
>
> Loads are not considered side effects currently, however. This works fine:
>
>   void bar(int *i) {
>     __builtin_assume(*i > 0);
>   }
>
> and, thus, my recommendation ;)

Some loads are side-effecting though, such as volatile loads:

int foo(volatile int *a) {
  return *a;
}

Can that be marked __attribute__((pure))? Or can pure access a
volatile global variable?

~Aaron

>
>
> http://reviews.llvm.org/D8548
>
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