https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121168
Bug ID: 121168
Summary: missed optimization with ubsan at -O3
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Blocks: 121165
Target Milestone: ---
Take:
```
int f1(int a, char *p)
{
char y = 0;
__SIZE_TYPE__ ttt = a != 0;
if (ttt == 1)
__builtin_memmove(&y, p, ttt);
return y;
}
int f(int a, char *p)
{
__SIZE_TYPE__ t = 1;
__SIZE_TYPE__ t1 = 0;
char y = 0;
__SIZE_TYPE__ *tt;
if (a)
tt = &t;
else tt = &t1;
__SIZE_TYPE__ ttt = *tt;
if (ttt == 1)
__builtin_memmove(&y, p, ttt);
return y;
}
```
These 2 functions should have the same code generation with `-O3
-fsanitize=undefined` but f produces worse code due to phiprop not handling the
prop here because of UBSAN_NULL but UBSAN_NULL expands to nothing for tt.
Note this shows up in complex C++ code is not as simple asking folks not to
write code like this.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121165
[Bug 121165] false positive Warray-bounds while building openmpt with -O3
-fsanitize=undefined
