[patch] A minor improvement for ARM setjmp and longjmp

[Jeff Johnston]

Patch applied.

-- Jeff J.

Kazu Hirata wrote:
> Hi,
>
> Attached is a patch to make a minor improvement for ARM setjmp and
> longjmp.
>
> A while ago, Nick fixed the problem of trying to save SP with STMEA in
>
> http://sourceware.org/ml/newlib/2008/msg00222.html
>
> Meanwhile, Paul independently came up with an alternative fix.
>
> Note that IP is a call-clobbered register.  As such, we do not have to
> save or restore it.  We can take advantage of this fact and ask STMEA
> to save IP after copying SP to IP.  This way, we are effectively
> saving SP without violating the constraints on STMEA.  We also get to
> reduce the number of loads by one.
>
> OK to apply?
>
> Kazu Hirata
>
> 2009-05-06  Paul Brook  <paul@codesourcery.com>
>
> 	* libc/machine/arm/setjmp.S: Don't bother saving IP.  Copy SP to
> 	IP before saving.  Likewise when restoring.
>
> Index: newlib/libc/machine/arm/setjmp.S
> ===================================================================
> RCS file: /cvs/src/src/newlib/libc/machine/arm/setjmp.S,v
> retrieving revision 1.3
> diff -u -d -p -r1.3 setjmp.S
> --- newlib/libc/machine/arm/setjmp.S	25 Apr 2008 09:02:40 -0000	1.3
> +++ newlib/libc/machine/arm/setjmp.S	5 May 2009 16:13:46 -0000
> @@ -121,8 +121,8 @@ SYM (\name):
>  
>  	/* Save all the callee-preserved registers into the jump buffer.  */
>  #ifdef __thumb2__
> +	mov		ip, sp
>  	stmea		a1!, { v1-v7, fp, ip, lr }
> -	str		sp, [a1],#+4
>  #else
>  	stmea		a1!, { v1-v7, fp, ip, sp, lr }
>  #endif
> @@ -149,7 +149,7 @@ SYM (\name):
>  	/* Restore the registers, retrieving the state when setjmp() was called.  */
>  #ifdef __thumb2__
>  	ldmfd		a1!, { v1-v7, fp, ip, lr }
> -	ldr		sp, [a1],#+4
> +	mov		sp, ip
>  #else
>  	ldmfd		a1!, { v1-v7, fp, ip, sp, lr }
>  #endif
>