https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126848
Bug ID: 126848
Summary: Repeated reads of an indeterminate value do not yield
the same value
Product: gcc
Version: 16.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: peppe at gcc dot gnu.org
Target Milestone: ---
Consider this testcase:
```
[[gnu::noipa]]
int g(int c)
{
int a;
int x = c ? a : 1;
return x - a;
}
int main()
{
return g(1);
}
```
On GCC 16.2 with -std=c++26 -O2, this program exits with 1.
Shouldn't it exit with 0? It is my understanding that, under P2795R5 / C++26
rules (implemented in GCC 16), re-reading the same indeterminate value is
indeed erroneous behavior, but it must still yield the same value back:
https://eel.is/c++draft/basic.indet#example-1
This means that `x-a` must be 0 if `c` is true, no matter what's the erroneous
value of `a`.
