[commit, spu] Fix (latent) ICE in spu_expand_mov

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Hello,

in a compiler build with Tom de Vries' new sign/zero extension elimination
pass added (http://gcc.gnu.org/ml/gcc-patches/2010-10/msg01529.html), I'm
seeing frequent internal compiler errors on the SPU.

The reason is that this new pass frequently generates move instructions
whose destination is a sub-word lowpart subreg.  Now the problem on the
SPU is some of those subregs are not directly valid (e.g. a SImode lowpart
of a DImode value cannot be implemented by just reinterpreting register
contents, but requires an actual shift due to the way values are laid out
in the 16-bit SPU registers).  The SPU move expander attempts to rewrite
moves to eliminate such invalid subregs.  However, it expects them to
occur only on the *source* of a move, never the destination.

Interestingly enough, this apparently never happens in a compiler without
the extension elimination pass.  On the other hand, such move instructions
seem to be valid RTL as far as I can see from the docs, so the SPU back-
end really ought to support them ...

The following patch fixes this problem by having the move expander
simply remove the subreg and perform the move in the inner mode.
This fixes the ICEs with the extension elimination pass.

Tested with no regressions on spu-elf.
Committed to mainline.

Bye,
Ulrich


ChangeLog:

	* config/spu/spu.md ("mov<mode>"): Use nonimmediate_operand
	predicate for destination operand.
	* config/spu/spu.c (spu_expand_mov): If move destination is an
	invalid subreg, perform move in the subreg's inner mode instead.

diff -urp gcc/config/spu.orig/spu.c gcc/config/spu/spu.c
--- gcc/config/spu.orig/spu.c	2010-12-10 16:51:16.000000000 +0100
+++ gcc/config/spu/spu.c	2010-12-21 16:49:02.000000000 +0100
@@ -4572,7 +4572,13 @@ int
 spu_expand_mov (rtx * ops, enum machine_mode mode)
 {
   if (GET_CODE (ops[0]) == SUBREG && !valid_subreg (ops[0]))
-    abort ();
+    {
+      /* Perform the move in the destination SUBREG's inner mode.  */
+      ops[0] = SUBREG_REG (ops[0]);
+      mode = GET_MODE (ops[0]);
+      ops[1] = gen_lowpart_common (mode, ops[1]);
+      gcc_assert (ops[1]);
+    }
 
   if (GET_CODE (ops[1]) == SUBREG && !valid_subreg (ops[1]))
     {
diff -urp gcc/config/spu.orig/spu.md gcc/config/spu/spu.md
--- gcc/config/spu.orig/spu.md	2010-12-10 16:51:16.000000000 +0100
+++ gcc/config/spu/spu.md	2010-12-21 16:57:27.000000000 +0100
@@ -269,8 +269,8 @@
 ;; mov
 
 (define_expand "mov<mode>"
-  [(set (match_operand:ALL 0 "spu_nonimm_operand" "=r,r,r,m")
-	(match_operand:ALL 1 "general_operand" "r,i,m,r"))]
+  [(set (match_operand:ALL 0 "nonimmediate_operand" "")
+	(match_operand:ALL 1 "general_operand" ""))]
   ""
   {
     if (spu_expand_mov(operands, <MODE>mode))
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com