[MLton-devel] Fwd: C back end for MLton

[Brad Lucier]

> 
> > > At some point (3.* ?) gcc became much more careful about inline asms.
> > > Perhaps you want to build gcc-3.2 (the latest release) and try it.
> > 
> > I just built gcc 3.2 on my machine and used it to recompile the MLton
> > runtime system without any warnings or errors.  Is it plausible that
> > something has changed between 3.2 and 3.3 to introduce the error
> > message?
> 
> I'll send it to the gcc mail list and see what comes back.

Here's what I got back from the gcc mail list:

>From aph@cambridge.redhat.com  Tue Nov  5 11:31:02 2002
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To: Brad Lucier <lucier@math.purdue.edu>
Cc: gcc@gcc.gnu.org
Subject: help with different treatment of asms in 3.2 and 3.3?
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Brad Lucier writes:
 > 3.2 compiles the following code without complaint (beyond the warnings)
 > and 3.3 rejects it.  The code is from the MLton ML compiler runtime; I
 > know nothing about inline asms; could someone offer some advice?
 >
 > int Int_quot(int numerator, int denominator) {
 >         register int eax asm("eax");
 >
 >         eax = numerator ;
 >
 >         __asm__ __volatile__ ("cdq\n        idivl %1"
 >                 :
 >                 : "r" (eax), "m" (denominator)
 >                 : "eax", "edx");
 >
 >         return eax;
 > }

Do this:

int Int_quot(int numerator, int denominator) {
  int eax;

  __asm__ __volatile__ ("cdq\n        idivl %2"
                        : "=a" (eax)
                        : "0" (numerator), "rm" (denominator)
                        : "edx");

  return eax;
}

Andrew.

>From matz@suse.de  Tue Nov  5 11:21:19 2002
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Date: Tue, 5 Nov 2002 17:21:17 +0100 (CET)
From: Michael Matz <matz@suse.de>
To: Brad Lucier <lucier@math.purdue.edu>
Cc: <gcc@gcc.gnu.org>
Subject: Re: help with different treatment of asms in 3.2 and 3.3?
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Hi again,

On Tue, 5 Nov 2002, Michael Matz wrote:

> GCC is right here.  You don't need (or want) to use register variables
> here.  A better way is:
>
> int Int_quot(int numerator, int denominator) {
>         __asm__ __volatile__ ("cdq\n        idivl %2"
>                 : "=a" (numerator)
>                 : "0" (numerator), "rm" (denominator)
>                 : "edx");
>
>         return numerator;
> }

I forgot to mention:  The use of asm is nonsensical here anyway.  A simple
  int Int_quot (int n, int d) { return n / d; }
produces exactly the same code.


Ciao,
Michael.



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