Re: ARM: new peephole to turn {add,sub}+cmp into {add,sub}s

[Richard Earnshaw <rearnsha at arm dot com>]

These are wrong.  Consider the overflow case.

R.

> Even though combine attempts to merge add and sub with cmp, it won't
> do that if there are other insns between them.  When the intervening
> insn is a store, it will typically be re-scheduled for execution after
> the cmp.  Then, these new peepholes will match the sequence of add/sub
> and cmp and arrange for us to use adds/subs instead.
> 
> Ok to install?
> 
> 
> Index: gcc/ChangeLog
> from  Alexandre Oliva  <aoliva@redhat.com>
> 
> 	* config/arm/arm.md (adds, subs): Define peepholes.
> 
> Index: gcc/config/arm/arm.md
> ===================================================================
> RCS file: /cvs/gcc/egcs/gcc/config/arm/arm.md,v
> retrieving revision 1.52
> diff -u -r1.52 arm.md
> --- gcc/config/arm/arm.md	2000/07/03 18:02:13	1.52
> +++ gcc/config/arm/arm.md	2000/07/06 20:03:58
> @@ -7793,6 +7793,28 @@
>    "sub%?s\\t%0, %1, #0"
>  [(set_attr "conds" "set")])
>  
> +;; Combine may miss these because of intervening insns before sched.
> +
> +(define_peephole
> +  [(set (match_operand:SI 0 "s_register_operand" "=r,r")
> +	(plus:SI (match_operand:SI 1 "s_register_operand" "r,r")
> +		 (match_operand:SI 2 "arm_add_operand" "rI,L")))
> +   (set (reg:CC 24)
> +	(compare:CC (match_dup 0) (const_int 0)))]
> +  ""
> +  "add%?s\\t%0, %1, %2"
> +[(set_attr "conds" "set")])
> +
> +(define_peephole
> +  [(set (match_operand:SI 0 "s_register_operand" "=r,r")
> +	(minus:SI (match_operand:SI 1 "s_register_operand" "r,r")
> +		  (match_operand:SI 2 "arm_add_operand" "rI,L")))
> +   (set (reg:CC 24)
> +	(compare:CC (match_dup 0) (const_int 0)))]
> +  ""
> +  "sub%?s\\t%0, %1, %2"
> +[(set_attr "conds" "set")])
> +
>  ; Peepholes to spot possible load- and store-multiples, if the ordering is
>  ; reversed, check that the memory references aren't volatile.
>  
> 
> 
> -- 
> Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
> Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
> CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
> Free Software Evangelist    *Please* write to mailing lists, not to me
>