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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103665] New: insert_trap in
 gimple-isolate-paths interferes badly with modref, pure-const and other
 optimizations
Date: Sat, 11 Dec 2021 22:03:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103665

            Bug ID: 103665
           Summary: insert_trap in gimple-isolate-paths interferes badly
                    with modref, pure-const and other optimizations
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

When we detect load/store of NULL memory we produce:
  _9 =3D{v} MEM[(union tree_node *)0B].base.code;=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  __builtin_trap ();=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20

The volatile memory store is intended to keep program segfaulting as it did
before. However this representation is bad because it is now considered a
significant side-effects.  This prevents such function from being discovere=
d as
pure/const and prevents other useful optimizations too=