(extendsfdf2): SFmode and DFmode register format identical so use define_expand...

(extendsfdf2): SFmode and DFmode register format identical so use
define_expand with paradoxical subreg no-op and accompanying new
define_split.

From-SVN: r8586

gcc/config/rs6000/rs6000.md

@@ -2500,6 +2500,10 @@
 ;; The only conversions we will do will be when storing to memory.  In that
 ;; case, we will use the "frsp" instruction before storing.
 ;;
+;; SFmode values are stored in DFmode registers with the same format as
+;; DFmode values, so float_extend is a no-op: treat as paradoxical subreg
+;; using define_expand and define_split if made by combine.
+;;
 ;; Note that when we store into a single-precision memory location, we need to
 ;; use the frsp insn first.  If the register being stored isn't dead, we
 ;; need a scratch register for the frsp.  But this is difficult when the store
@@ -2507,18 +2511,26 @@
 ;; this case, we just lose precision that we would have otherwise gotten but
 ;; is not guaranteed.  Perhaps this should be tightened up at some point.
 
-(define_insn "extendsfdf2"
+(define_expand "extendsfdf2"
   [(set (match_operand:DF 0 "gpc_reg_operand" "=f")
-	(float_extend:DF (match_operand:SF 1 "gpc_reg_operand" "f")))]
+	(match_operand:SF 1 "gpc_reg_operand" "f"))]
   ""
-  "*
+  "
 {
-  if (REGNO (operands[0]) == REGNO (operands[1]))
-    return \"\";
-  else
-    return \"fmr %0,%1\";
-}"
-  [(set_attr "type" "fp")])
+  if (GET_CODE (operands[1]) == SUBREG)
+     operands[1] = force_reg (SFmode, operands[1]);
+  operands[1] = gen_rtx (SUBREG, DFmode, operands[1], 0);
+}")
+
+(define_split
+  [(set (match_operand:DF 0 "gpc_reg_operand" "")
+	(float_extend:DF (match_operand:SF 1 "gpc_reg_operand" "")))]
+  "GET_CODE (operands[1]) != SUBREG"
+  [(set (match_dup 0) (match_dup 1))]
+  "
+{
+  operands[1] = gen_rtx (SUBREG, DFmode, operands[1], 0);
+}")
 
 (define_insn "truncdfsf2"
   [(set (match_operand:SF 0 "gpc_reg_operand" "=f")