Mail Archives: djgpp/1996/11/28/10:27:07
On Thu, 28 Nov 1996, Glen Miner wrote:
> > There's a whole chapter on optimization options in the GCC on-line docs.
>
> Hmm, I was skimming through the info directory and couldn't find exactly
> what I was looking for. I'll look closer.
Type this from the DOS prompt:
info gcc invoking optimize
> Hmm, I'll look into this. I'm not so sure that I can do without a frame
> pointer, though. How would it use local variables then?
Trust GCC, it can.
> > Mixing 16-bit and 32-bit code will usually *slow down* your program by
> > about a factor of 2, due to the override prefixes which eat up a cycle.
>
> This is quite odd. I'm going to have to re-read the old pmode optimizing
> doc I have lying around somewhere.
This has nothing to do with PM vs RM (except that most RM code uses
16-bit instructions). The issue here is that using 16-bit instructions
in a middle of 32-bit code requires an operand size prefix and/or and
address size prefix, and each of these eats up one cycle on an i486 (0 on
an i386, and I don't have information about the Pentium and Pro).
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