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Date: Tue, 11 Apr 2000 11:09:40 +0200
From: Gautier <gautier DOT demontmollin AT maths DOT unine DOT ch>
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Subject: Re: inefficiency of GCC output code & -O problem
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"Alexei A. Frounze":

> Well, but it work with registers even when value needs to be zeroed, shifted and
> so on. It loads registers in very simple situations, where possible to adjust
> some bytes and we're done.

What appears to me is that among a set of time-optimising variants, GCC doesn't
seem to choose the most space-optimising one. But maybe the values of registers
are re-used later in your code ? Some <32 bit manipulations are said to slow
down a lot the Pentium-class processors.

> > On Intel x86s there is not much to do - there are so few registers - but
> > anyway GCC is very smart at register mapping !

> Not a few. That's enough.

Well... but _compared_ to other processors the choice of registers is very poor.

> I don't think GCC is a very good optimizing compiler. Anyway it has something
> over other compilers: it's free, it's portble and multiplatform.

There are surely improvements till reaching Watcom C or Lahey Fortran that are
written with Intel code generation in mind.
But who knows (with the latest ecgs & Co ?)

> It always works this way. So I forced my functions to have only 32-bit
> parameters and return values. This solves this ugly problem.

> > You should try an equivalent test on a very
> > strong typed GCC front-end like GNAT...

> What's GNAT?

The GNU Ada95. You can see Ada95 as a standardized Turbo Pascal with some
enhancements. Since type conversions are explicit (unlike TP for the 8/16/32
bit integers), you detect the "ugly problems" at source :-).

______________________________________________________
Gautier  --  http://members.xoom.com/gdemont/gsoft.htm