Re: eliminate dead stores across functions

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Mar 6, 2018 at 1:00 PM, Prathamesh Kulkarni
<prathamesh.kulkarni@linaro.org> wrote:
> Hi,
> For the following test-case,
>
> int a;
>
> __attribute__((noinline))
> static void foo()
> {
>   a = 3;
> }
>
> int main()
> {
>   a = 4;
>   foo ();
>   return a;
> }
>
> I assume it's safe to remove "a = 4"  since 'a' would be overwritten
> by call to foo ?
> IIUC, ipa-reference pass does mod/ref analysis to compute side-effects
> of function call,
> so could we perhaps use ipa_reference_get_not_written_global() in dse
> pass to check if a global variable will be killed on call to a
> function ? If not, I suppose we could write a similar ipa pass that
> computes the set of killed global variables per function but I am not
> sure if that's the correct approach.

Do you think the situation happens often enough to make this worthwhile?

ipa-reference doesn't compute must-def, only may-def and may-use IIRC.

Richard.

> Thanks,
> Prathamesh