Virtual Methods hurting performance in the DMD frontend

[Stefan Koch via Digitalmars-d]

Hi,

As you may know I am currently optimizing template-related code 
inside of DMD.
Inside DMD code quality is quite high, there is little low 
hanging fruit.

However there is one thing that suspiciously often shows up the 
on profilers display.
Those are indirect class which have a high number of L2(!) 
i-cache misses.

These calls don't do a lot of work. They are needed either for 
downcasts or to verify the dynamic type of an AST-Node.
Even without the i-cache related stalls the call overhead alone 
is something to think about.

For template-heavy code matching template parameters is one of 
the most frequently operations.
Since Template Parameters can be types expressions or symbols the 
dynamic-types are heavily queried.

First experiments suggest that a speedup of around 12% is 
possible if the types where accessible directly.

Since dmd uses visitors for many things now the benefit of 
virtual methods is highly reduced.

Please share your thoughts.

Cheers,
Stefan