[fpc-devel] Another benefit of pure functions

[J. Gareth Moreton]

This is for my own benefit and note-taking, but I've just found another 
use for pure functions.

Though this is not exactly how the compiler source is structured, you 
get situations such as this.

RegName := debug_regname(taicpu(p).oper[0]^.reg); { 32-bit register name }
DebugMsg(SPeepholeOptimization + PreMessage + RegName + ',' + RegName + 
' (removes REX prefix)', p);

When not in debug mode, DebugMsg is just a null procedure that does 
nothing (as is debug_regname, but let's ignore that for the moment).

One of the definitions of pure functions is that it has no side-effects, 
so if it can be shown that RegName is not used after its assignment, and 
a pure function is being used to assign said value, then the entire call 
can be safely removed, since it won't affect any other part of the program.

If anyone is able to notice potential areas where pure functions can 
optimise a program, sound off!

Gareth aka. Kit


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