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Re: eliminate dead stores across functions
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Tue, 6 Mar 2018 15:28:29 +0100
- Subject: Re: eliminate dead stores across functions
- Authentication-results: sourceware.org; auth=none
- References: <CAAgBjMkcuch04W94DB06Vv7oYZQPLk2VRN5ALd_0Vt=CmzZ=-w@mail.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