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From: cbramix AT libero DOT it
Newsgroups: comp.os.msdos.djgpp
Subject: Re: missing optimization?
Date: 8 Nov 2005 00:58:41 -0800
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Hello,
It's exactly you wrote into your commented assembly: the TEST opcode
isn't needed.
But as I wrote before, that instruction isn't emitted if I use a
previous version, so I was wondering if the code could rewritten in a
better way.
I make you another small example: let's see these C lines:

(my_structure+0)->data = my_var++;
(my_structure+1)->data = my_var++;

The compiler generates this:

movl   %ebx, %eax
leal   1(%ebx), %ebx
movl   %eax, (%esi)
movl   %ebx, %eax
leal   1(%ebx), %ebx
movl   %eax, 4(%esi)

But if I rewrite it to:

(my_structure+0)->data = my_var;
(my_structure+1)->data = ++my_var;
my_var++;

I get this:

movl   %ebx, (%esi)
incl   %ebx
movl   %ebx, 4(%esi)
incl   %ebx

DJ said it's probably better to forward this message to GCC mailing
list and now I'm going to believe he's right.
Thank you for your help.

Sincerely,

Carlo Bramini