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From: "bugdal at aerifal dot cx" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/95558] New: Invalid IPA optimizations based on weak
 definition
Date: Sat, 06 Jun 2020 03:45:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95558

            Bug ID: 95558
           Summary: Invalid IPA optimizations based on weak definition
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bugdal at aerifal dot cx
  Target Milestone: ---

Created attachment 48689
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D48689&action=3Dedit
test case

Here is a case that came up in WIP code on musl libc, where I wanted to pro=
vide
a weak dummy definition for functionality that would optionally be replaced=
 by
a strong definition elsewhere at ld time. I've been looking for some plausi=
ble
explanation aside from an IPA bug, like interaction with UB, but I can't fi=
nd
any.

In the near-minimal test case here, the function reclaim() still has all of=
 the
logic it should, but reclaim_gaps gets optimized down to a nop.

What seems to be happening is that the dummy weak definition does not leak =
into
its direct caller via IPA optimizations, but does leak to the caller's call=
er.=