perf: use a monomorphic impl for CCMonomorphic.{min,max}

[c-cube]

close #452

[FardaleM]

From my testing, it seems enough to define min as:

let min (x:int) (y:int) = if x <= y then x else y

But my testing was with flambda enabled. Something that might be enough also is to do:

let min (x:int) (y:int) = Stdlib.min x y

But I did not try it to see if this is enough. With both solution we would not need the conditional compilation.

[c-cube]

let min (x:int) (y:int) = Stdlib.min x y

I've never seen before this be faster than let min = Stdlib.min? :/ if it is, we have a problem cause this is also how compare, etc are done. But anyway, I'd rather delegate to Int.min since it might become an intrinsic in the future.

[FardaleM]

I would need to look how it is compiled. The question is, does the compiler specialised the compare function or not. If not, then it goes through the polymorphic compare which is slow. That's how I found it, the min function was calling the runtime C function on my case. We would need to check if this is the case also for the other functions. But I don't know how to check that.

[c-cube]

Easiest is godbolt (https://ocaml.godbolt.org/), e.g.

https://ocaml.godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:ocaml,selection:(endColumn:58,endLineNumber:4,positionColumn:58,positionLineNumber:4,selectionStartColumn:58,selectionStartLineNumber:4,startColumn:58,startLineNumber:4),source:'%0Alet+cint+:+int+-%3E+int+-%3E+int+%3D+Stdlib.compare%0Alet+()+%3D%0A++Printf.printf+%22%25d%5Cn%22+(Sys.opaque_identity+(cint+42+41))'),l:'5',n:'1',o:'OCaml+source+%231',t:'0')),k:50,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:ocaml5000flambda,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'1',intel:'0',libraryCode:'0',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:ocaml,libs:!(),options:'',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+ocamlopt+5.0.0-flambda+(Editor+%231)',t:'0')),k:50,l:'4',n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4

-- Simon Cruanes

[FardaleM]

I tried to play to see the case for min, but I don't see the function, so I don't know how to interpret this.

[c-cube]

it might be because polymorphic min isn't in the compiled code, it's part of the runtime.