https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98049
Bug ID: 98049
Summary: False positive when compiling with -Os
-Wmaybe-uninitialized
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: ahmad at a3f dot at
Target Milestone: ---
Created attachment 49642
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49642&action=edit
C Source reproducing the erroneous warning
gcc -Os warns that "'start' may be used uninitialized in this function
[-Wmaybe-uninitialized]" in this snippet:
unsigned start;
if (timeout)
start = get_time();
while (!active()) {
if (timeout && is_timeout(start, timeout))
~~~~~~~~~~^~~~~~~~~~~~~~~~
return 1;
}
This is wrong, because `start' is only evaluated when `timeout' != 0
at which time it's always initialized. `timeout' is automatic storage and can't
change in-between.
The warning vanishes if -Os is removed or code around is moved.
Steps to reproduce (or check https://godbolt.org/z/3qf58T):
$ cc minim.c -c -Os -Wmaybe-uninitialized
<source>: In function 'void f(int, unsigned int)':
<source>:12:42: warning: 'start' may be used uninitialized in this function
[-Wmaybe-uninitialized]
12 | if (timeout && is_timeout(start, timeout))
| ~~~~~~~~~~^~~~~~~~~~~~~~~~
<source>:7:18: note: 'start' was declared here
7 | unsigned start;
| ^~~~~
