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From: "slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98499] [11 Regression] Possibly bad std::string initialization in constructors
Date: Wed, 06 Jan 2021 23:11:24 +0000 [thread overview]
Message-ID: <bug-98499-4-ZokGfaNDDG@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98499-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98499
--- Comment #6 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #5)
> Possibly in discovering pure/constness. See uses of
> gimple_call_return_slot_opt_p in tree-ssa-structalias.c
Aha, that's useful!
Trying to understand the problem better myself: `-fdump-tree-all` has seemingly
relevant `036t.ealias` that precedes breaking `037t.fre1`.
I assume `036t.ealias` analyses individual functions locally and does not take
into account other details, thus main() analysis should be enough:
```
...
Points-to sets
ANYTHING = { ANYTHING }
ESCAPED = { ESCAPED NONLOCAL }
NONLOCAL = { ESCAPED NONLOCAL }
STOREDANYTHING = { }
INTEGER = { ANYTHING }
_ZN8ImporterC1Ev = { }
imp.0+64 = { ESCAPED NONLOCAL } same as _6
imp.64+8 = { ESCAPED NONLOCAL }
__builtin_trap = { }
main = { }
CALLUSED(9) = { ESCAPED NONLOCAL imp.0+64 imp.64+8 } same as callarg(11)
CALLCLOBBERED(10) = { ESCAPED NONLOCAL imp.0+64 imp.64+8 } same as callarg(11)
callarg(11) = { ESCAPED NONLOCAL imp.0+64 imp.64+8 }
_6 = { ESCAPED NONLOCAL }
Alias information for int main()
Aliased symbols
imp, UID D.2146, struct Importer, is addressable
Call clobber information
ESCAPED, points-to non-local, points-to vars: { }
Flow-insensitive points-to information
_6, points-to non-local, points-to escaped, points-to NULL, points-to vars: { }
int main ()
{
struct Importer imp;
char * _6;
<bb 2> :
Importer::Importer (&imp);
_6 = MEM[(struct string *)&imp]._M_buf;
if (&MEM[(struct string *)&imp]._M_local_buf != _6)
goto <bb 3>; [0.00%]
else
goto <bb 4>; [100.00%]
<bb 3> [count: 0]:
__builtin_trap ();
<bb 4> :
imp ={v} {CLOBBER};
imp ={v} {CLOBBER};
return 0;
}
```
I think this looks correct. As I understand we care about a few things in the
analysis here:
1. imp.0+64 and _6 both point to the same flow-insensitive classes (both are
ESCAPED NONLOCAL)
2. imp.0+64 and _6 both point to the same field in flow-sensitive analysis
(both do according to `imp.0+64 = { ESCAPED NONLOCAL } same as _6`.
I don't see problems here.
Mechanically looking at incorrect gcc's decision for `imp.0+64 != _6`:
ptrs_compare_unequal(
ptr1 = &MEM[(struct string *)&imp]._M_local_buf,
ptr2 = _6
)
returns `TRUE` because
pt_solution_includes(
info = ptr2->pt,
obj1 = imp
)
returns `FALSE`. That seems to be a bug.
Do arguments to `pt_solution_includes` look correct so far? Does it try to
answer "could _6 point at any field of 'imp' type"?
next prev parent reply other threads:[~2021-01-06 23:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-02 11:11 [Bug c++/98499] New: " slyfox at gcc dot gnu.org
2021-01-02 22:22 ` [Bug c++/98499] " slyfox at gcc dot gnu.org
2021-01-03 11:44 ` slyfox at gcc dot gnu.org
2021-01-03 20:56 ` slyfox at gcc dot gnu.org
2021-01-03 21:50 ` slyfox at gcc dot gnu.org
2021-01-04 12:28 ` marxin at gcc dot gnu.org
2021-01-05 11:09 ` rguenth at gcc dot gnu.org
2021-01-06 23:11 ` slyfox at gcc dot gnu.org [this message]
2021-01-07 8:12 ` [Bug tree-optimization/98499] " rguenth at gcc dot gnu.org
2021-01-10 18:39 ` slyfox at gcc dot gnu.org
2021-01-28 10:55 ` hubicka at gcc dot gnu.org
2021-01-30 18:02 ` slyfox at gcc dot gnu.org
2021-02-01 18:14 ` cvs-commit at gcc dot gnu.org
2021-02-01 18:39 ` slyfox at gcc dot gnu.org
2021-02-01 18:40 ` slyfox at gcc dot gnu.org
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