https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103830
Bug ID: 103830
Summary: volatile optimized away
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: bernd.edlinger at hotmail dot de
Target Milestone: ---
the following test case is intentionally writing at address 0,
it is IMHO invalid to optimize it away (at -Og):
$ cat empty-inline.cc
/* This testcase is part of GDB, the GNU debugger.
Copyright 2021 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
/* PR 25987 */
struct MyClass;
struct ptr {
MyClass* get() { return t; } /* line 21 */
MyClass* t;
};
struct MyClass { void call(); };
void MyClass::call() {
*(volatile char*)(nullptr) = 1; /* line 26 */
}
static void intermediate(ptr p) {
p.get()->call(); /* line 29 */
}
int main() {
intermediate(ptr{new MyClass});
}
/* EOF */
previously this used to SIGSEGV in line 26, but no longer with
git master from December 18th at least.
I think it is rather common to have something at address zero,
for instance interrupt tables or device registers,
and therefore it's not OK to optimize those volatile accesses away.
