🚀 go-pugleaf

(I primarily posted this to comp.lang.c++, but the conclusion of it
 make it fit to this ng -- unless I'm too ignorant about compiler
 optimization....)

A question arose during a flamewar on comp.lang.fortran, about compiler
optimization.

C has always been the language where _THE PROGRAMMER_ could make his
own optimization, but this style of programming is getting deprecated
according to most C++ who basically say "rely on the compiler, optimize
only as a last minute operation". But here I have an example of what
would be very unefficient in C/C++ compared to F90:

> for (i = 0 ; i < n ; i++) {
>    for (j = 0 ; j < n ; j++) {
>       a[i][j] = b[i][j] * c[i] ;
>    }
> }

> do j = 1,m
>   do i = 1, n
>     a (i,j) = b(i,j) * c(i)
>   enddo
> enddo 

The Fortran compiler can easy unroll the loop and take advantage of scalar
caches, and easily use vectorial registers, whereas the C compiler
can't even move the evaluation of c[i] out of the inner loop because
&c[i] could be == to &a[x][y] ............ That's the problem with
weak typin... I'm wondering if any of the "const" tweak would change
anything...
Despite I'm really disgusted by Fortran, I must concede this and
since only few compilers do really perform all the optimizations you
see in the books, I don't know they could get sthng good out of this...

So, if we're obliged to barf (see note) in this case, could there be any kind
of C++ extension -- another one! -- to imporve this? 

Barf [ba:rf] 2. v. "He suggested using Fortran. We all barfed." 
(From the Shokagukan dict, according to f2c.h)

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