gdc or ldc for faster programs?

[Elronnd]

On Tuesday, 25 January 2022 at 22:33:37 UTC, H. S. Teoh wrote:
> interesting because idivl is known to be one of the slower 
> instructions, but gdc nevertheless considered it not worthwhile 
> to replace it, whereas ldc seems obsessed about avoid idivl at 
> all costs.

Interesting indeed.  Two remarks:

1. Actual performance cost of div depends a lot on hardware.  
IIRC on my old intel laptop it's like 40-60 cycles; on my newer 
amd chip it's more like 20; on my mac it's ~10.  GCC may be 
assuming newer hardware than llvm.  Could be worth popping on a 
-march=native -mtune=native.  Also could depend on how many ports 
can do divs; i.e. how many of them you can have running at a time.

2. LLVM is more aggressive wrt certain optimizations than gcc, by 
default.  Though I don't know how relevant that is at -O3.