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To: Boris Boesler <baembel@gmx.de>
Cc: GCC <gcc@gcc.gnu.org>
Subject: Re: Allocating scratch register
References: <35528597-A9DA-4D81-8EE4-4192FE591628@gmx.de>
From: Ian Lance Taylor <iant@google.com>
Date: Wed, 09 Jan 2008 22:55:00 -0000
In-Reply-To: <35528597-A9DA-4D81-8EE4-4192FE591628@gmx.de>
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Boris Boesler <baembel@gmx.de> writes:

>   I'm trying to allocate a scratch register: write immediate constant  
> into scratch register r, write register r into memory
> 
> ;; write imm into memory
> (define_insn_and_split "mov<mode>_imm_by_store"
>    [(set (match_operand:I8I16 0 "memory_operand"    "=m")
> 	(match_operand:I8I16 1 "immediate_operand" " i"))
>    (clobber (match_scratch:I8I16 2 "=r"))]
>    ""
>    "#"
>    ""
>    [(parallel
>      [(set (match_dup 2) (match_dup 1))
>       (set (match_dup 0) (match_dup 2))])]
>    ""
> )
> 
>   I found that in a mips back-end. But this pattern is not recognized  
> during code-generation [char c1; c1 = 1;]:
> simple-memory.c:19: error: unrecognizable insn:
> (insn 12 11 14 3 (set (mem/c/i:QI (reg/f:SI 105) [0 c1+0 S8])
>          (const_int 1 [0x1])) -1 (nil)
>      (nil))
> 
>   If I remove the clobber command and replace (match_dup 2) by  
> (reg:I8I16 A15_REGNUM) code will be generated (but not as wanted).
> 
>   What is wrong with the code above?

There is nothing wrong with that code, but nothing is going to make
the compiler use it.  Moves are special.  If you need a scratch
register to do a move, then you need to look at the
TARGET_SECONDARY_RELOAD hook.

But if the problem is only that you need a register to store a
constant into memory, then you should be able to do that using
register constraints on your mov<mode> insn.

Ian