missed optimization with return statement in function

[1-Olivier]

Consider this trivial shader:

vector foo(string a)
{
    if( a == "" )
        return 0;
    return 1;
}

surface simple(string s = "")
{
    P += foo(s);
}

running testshade --debug simple.oso yields, among a wall of text:

Optimized 8 ops to 6 (-25.0%)
Globals written: (1)  P

A simple change to the function:

vector foo(string a)
{
    if( a == "" )
        return 0;
    else
        return 1;
}

and the output is now:

Optimized 9 ops to 1 (-88.9%)
Globals written: (0)

I would expect the original function to allow the same optimization.

Versions

• OSL branch/version: 1.10.9 (testshade output above) / 3d0a284 (where I originally found the issue in a larger network)
• OS: linux
• LLVM version: 9.0.1 / 6.0.0