From: Scott Wood <scottwood@freescale•com>
To: Kevin Diggs <kevdig@hypersurf•com>
Cc: linuxppc-dev@ozlabs•org
Subject: Re: inline assembly
Date: Wed, 04 Jun 2008 14:45:04 -0500 [thread overview]
Message-ID: <4846F0C0.80808@freescale.com> (raw)
In-Reply-To: <4846EEAE.3000908@hypersurf.com>
Kevin Diggs wrote:
> Hi,
>
> When doing inline assembly, is there a way to get the compiler to
> assign "extra" (one not specified for inputs and outputs) registers? In
> the following:
>
> __asm__ __volatile__ (
> "addi 5,%1,-1\n"
> "andc 5,%1,5\n"
> "cntlzw 5,5\n"
> "subfic %0,5,31":
> "=r"(j):
> "r"(i)
> );
>
> Can I get the compiler to choose a register for r5?
Yes, like this:
int tmp;
asm volatile("addi %1, %2, -1;"
"andc %1, %2, %1;"
"cntlzw %1, %1;"
"subfic %0, %1, 31" : "=r" (j), "=&r" (tmp) : "r" (i));
However, it'd be better to let the compiler do more, by just using the
existing cntlzw() function.
-Scott
next prev parent reply other threads:[~2008-06-04 19:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-04 19:36 inline assembly Kevin Diggs
2008-06-04 19:45 ` Scott Wood [this message]
2008-06-05 10:44 ` David Howells
2008-06-05 16:52 ` Scott Wood
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