Re: [PATCH GIT 0.6] make use of register variables & size_t

[Matthias-Christian Ott]

Matthias-Christian Ott wrote:
> Rene Rebe wrote:
>
> > Hi,
> >
> > Matthias-Christian Ott wrote:
> >
> > > The "git" didn't try store small variables, which aren't referenced, 
> > > in the processor registers. It also didn't use the size_t type. I 
> > > corrected a C++ style comment too.
> >
> >
> >
> > Well, modern compilers take register as a non-binding hint. Your 
> > register storage specification for those loop counters will not make 
> > any change. You have not looked into the resulting binary?
> >
> > Also // is valid C99 ...
> >
> > Yours,
> But if you use only /* */ comments and there's a // comment it looks 
> ugly :).
>
> I've disassembled the code and it for me (I'm not a professional 
> assembler coder) it looks like it's stored in a register because the ebp 
> offsets are smaller and the gcc (4.0) wouldn't cause an error if you 
> reference them.
>
> Matthias-Christian Ott
> -
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Here's some example code (diff of the assembler codes) which shows what 
I mean:

-       movl    %eax, -8(%ebp)
+       movl    %eax, -4(%ebp)
[..]
-       leal    1(%eax), %ecx
-       movl    -52(%ebp), %edx
+       leal    1(%eax), %edx
        movl    12(%ebp), %eax
-       subl    %edx, %eax
-       movl    %eax, %edx
-       movl    -52(%ebp), %eax
+       movl    %eax, %ecx
+       subl    -80(%ebp), %ecx
+       movl    -80(%ebp), %eax
        sall    $2, %eax
        movl    %eax, %ebx
        addl    8(%ebp), %ebx

-
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