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From: "hubicka at kam dot mff.cuni.cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103168] Value numbering for PRE of pure
 functions can be improved
Date: Mon, 22 Nov 2021 15:14:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103168

--- Comment #12 from hubicka at kam dot mff.cuni.cz ---
> unsigned p;
> unsigned __attribute__((noinline)) test (void)
> {
>   return p;
> }
>=20
> modref analyzing 'test' (ipa=3D0) (pure)
>  - Analyzing load: p
>    - Recording base_set=3D0 ref_set=3D0
>  - modref done with result: tracked.

Modref does not record accesses to global vars as known baes and just as
accesses relative to MODREF_UNKONWN_PARM (since ipa-reference does this)
So only useful info it collect from loads/stores is the alias set and
here it is 0 (why?).=20
Then it drops the summary as useless since function is detected as pure
earlier and that holds the same info.=