https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96629
Bug ID: 96629
Summary: spurious uninitialized variable warning with branches
at -O1 and higher
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yyc1992 at gmail dot com
Target Milestone: ---
Reduced test code:
```
int mem(char *data);
int cond(void);
void f(char *data, unsigned idx, unsigned inc)
{
char *d2;
int c = cond();
if (idx >= 2) {
if (c)
d2 = data;
mem(data);
}
else if (inc > 3) {
if (c)
d2 = data;
mem(data);
}
else {
if (c) {
d2 = data;
}
}
if (*data) {
}
else if (c) {
mem(d2);
}
}
```
Compiling with `gcc -Wall -Wextra -O{1,2,s,3,fast}` warns about
```
a.c: In function 'f':
a.c:27:9: warning: 'd2' may be used uninitialized in this function
[-Wmaybe-uninitialized]
27 | mem(d2);
| ^~~~~~~
```
However, it should be clear that `d2` is always assigned when `c` is true. In
fact, it seems that GCC could figure this out in some cases. Changes that can
surpress the warning includes,
1. Remove any of the `mem(data)` calls.
2. Remove any one of the `if`s (leaving only the if or else branch
unconditionally)
3. Change first condition to be on inc instead.
4. Removing the last `*data` branch.
Version tested:
AArch64: 10.2.0
ARM: 9.1.0
x86_64: 10.1.0
mingw64: 10.2.0
