[fpc-pascal] why fpc do not use a known return function value

[leledumbo]

> int c ; 
> int test( int p){ 
>   int i; 
>   i = p; 
>   return (i+2+c+2+c+2+c); 
> } 
> int main(){ 
>   c = test(128); 
> }

Hmm....yes, from C perspective, there's nothing can modify c before it's
used the first time (unless you inject the startup code). Therefore, the
compiler is safe to assume that c is its initial global value (0) and is
able to use constant propagation, with c assumed as constant to reduce the
function call into a simple value.

The case with Pascal is not the same, however. Pascal has unit system with
initialization section that can inject code before the main block is
executed. A unit can extern-ize the variable and modify it in its
initialization section. So it's not safe to assume the same thing as C does
above. It's not impossible, but would be harder to implement, probably
requiring whole program analysis.



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