https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115636
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So looking at what LLVM does (Note it does not handle the original case here).
It only handles the simple:
`1 << (a ? b : 1000)` cases.
That is:
```
int f0(int a, int b)
{
if (a) b = 1000;
int t = 1 << b;
return t;
}
```
is optimized to `1 << b` without the condition.
But once you add something more complex in the condition, it does not do
anything:
```
int g();
int f1(int a, int b)
{
if (a) b = 1000;
else b = g();
int t = 1 << b;
g();
return t;
}
int f2(int a, int b)
{
if (a) b = 1000;
else g();
int t = 1 << b;
g();
return t;
}
```
changing f0 to be:
```
if (a) t = 0;
else t = 1 << b;
```
Generates worse code for that.
I have to think this one through a little more I think ...
undefined behavior is fun.
