[ILUG] a quick gcc microoptimisation question

[Paul Jakma]

On Thu, 16 Dec 2004, Justin Mason wrote:

> In other words, with gcc optimisation, is the branch instruction used for
> the "if" case or the "else" case by default?

Does it matter? It comes down to:

   <instructions to evaluate conditional>
   bne <label1>
   <instructions for case1>
   jmp <label2>
.label1:
   <instructions for case2>
.label2:
   <rest of programme>

The other case is exact same except with a branch-on-equal instead of 
not-equal and the cases reversed. There's no difference really.

If either of the cases is anything more than a trivial amount of 
code, put it in a function - that will help more than anything else 
on modern CPUs.

regards,
-- 
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
If you had better tools, you could more effectively demonstrate your
total incompetence.