https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104549
Bug ID: 104549
Summary: Missing variable at O2/O3 likely caused by
-fearly-inlining
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: assaiante at diag dot uniroma1.it
Target Milestone: ---
In the following testing code, local variable i, which gets passed as argument
to a function defined in an external module, is not visible upon the call when
debugging. This behavior only occurs when the optimization level is O2 or O3.
$ cat a.c
void a()
{
int i = 0;
for (; i ; ) {}
test(i)
;
}
int main()
{
a();
}
$ cat lib.c
#include <stdio.h>
void nop() {
printf("\n");
}
void test(int i) {
printf("%d", i);
}
GCC and GDB version (GCC commit id: 500d3f0a302):
$ gcc --version
gcc (GCC) 12.0.0 20211227 (experimental)
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ gdb --version
GNU gdb (GDB) 11.2
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
GDB trace:
$ gcc -O2 -g a.c lib.c -o opt # <- same exact with O3
$ gdb -q opt
Reading symbols from opt...
(gdb) b 5
Breakpoint 1 at 0x400460: /home/stepping/66/reduce/a.c:5. (2 locations)
(gdb) r
Starting program: /home/stepping/66/reduce/opt
Breakpoint 1, main () at a.c:5
5 test(i)
(gdb) info locals
No locals.
Through some testing we found out that the optimization flag that introduces
the bug is likely -fearly-inlining, which makes main() call the test() function
directly. Indeed, if we add the flag -fno-early-inlining to the compilation
command line used above, the variable i will appear in the current frame with
its value correctly available.
