Performance issue with @fastmath and vectorization

[Johan Engelen via digitalmars-d-ldc]

On Saturday, 12 November 2016 at 15:44:28 UTC, deXtoRious wrote:
>
> I have not found any way to make LDC perform the same 
> optimizations as Clang's best case (simply static void, no weak 
> attribute) and have run out of ideas. Furthermore, I have no 
> idea why the aforementioned changes in the function declaration 
> affect the both optimizers in this way, or whether finer 
> control over vectorization/loop unrolling is possible in LDC. 
> Any thoughts?

I think that perhaps when inlining the fastmath function, some 
optimization attributes are lost somehow and the inlined code is 
not optimized as much (you'd have to specify @fastmath on main 
too).

It'd be easier to compare with -ffast-math I guess ;-)

A look at the generated LLVM IR may provide some clues.