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[PATCH]: Handle MODE_CC in gen_lowpart_common

Dave Anglin recently wrote:
> 2) The CSE pass can't simplify conditional jumps involving
>    CC_MODE registers because gen_lowpart_common doesn't handle
>    CC_MODE.  As a result, the state of a CC_MODE register doesn't
>    get recorded and the if_then_else can't be simplified.

The patch below addresses this deficiency allowing gen_lowpart_common
to interpret integer constants as CC_MODE values.  This allows CSE to
simplify the code example given in PR optimization/8705 on PA-Risc.

The following patch has been tested on both i686-pc-linux-gnu and
hppa2.0w-hp-hpux11.00 with a full "make bootstrap", all languages
except Ada and treelang, and regression checked with a top-level
"make -k check" with no new failures on either platform.

Ok for mainline?

2003-04-22  Roger Sayle  <roger at eyesopen dot com>
	    John David Anglin <dave dot anglin at nrc-cnrc dot gc dot ca>

	* emit-rtl.c (gen_lowpart_common): Handle interpreting integer
	constants as condition code values.

Index: emit-rtl.c
RCS file: /cvs/gcc/gcc/gcc/emit-rtl.c,v
retrieving revision 1.323
diff -c -3 -p -r1.323 emit-rtl.c
*** emit-rtl.c	17 Apr 2003 23:31:40 -0000	1.323
--- emit-rtl.c	22 Apr 2003 16:14:42 -0000
*************** gen_lowpart_common (mode, x)
*** 1290,1295 ****
--- 1290,1303 ----
+   /* If X is a CONST_INT or a CONST_DOUBLE, and MODE is a condition code
+      convert the constant into either const0_rtx or const_true_rtx.  */
+   else if (GET_MODE_CLASS (mode) == MODE_CC
+ 	   && GET_MODE (x) == VOIDmode
+ 	   && (GET_CODE (x) == CONST_INT || GET_CODE (x) == CONST_DOUBLE))
+     {
+       return x == const0_rtx ? const0_rtx : const_true_rtx;
+     }

    /* Otherwise, we can't do this.  */
    return 0;

Roger Sayle,                         E-mail: roger at eyesopen dot com
OpenEye Scientific Software,         WWW:
Suite 1107, 3600 Cerrillos Road,     Tel: (+1) 505-473-7385
Santa Fe, New Mexico, 87507.         Fax: (+1) 505-473-0833

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