PDP11: Use a mode with `const_double_zero' expressions

PDP11: Use a mode with `const_double_zero' expressions

For predictable semantics propagate the mode from operands referred by
FP substitutions to the `const_double_zero' expressions used with the
associated condition code calculation, resulting in the following update
to insn-emit.c code produced for the `pdp11-aout' target (with machine
description line numbering change noise removed):

@@ -1514,7 +1514,7 @@
 	gen_rtx_COMPARE (CCmode,
 	gen_rtx_ABS (DFmode,
 	operand1),
-	CONST_DOUBLE_ATOF ("0", VOIDmode))),
+	CONST_DOUBLE_ATOF ("0", DFmode))),
 		gen_rtx_SET (operand0,
 	gen_rtx_ABS (DFmode,
 	copy_rtx (operand1)))));
@@ -1555,7 +1555,7 @@
 	gen_rtx_COMPARE (CCmode,
 	gen_rtx_NEG (DFmode,
 	operand1),
-	CONST_DOUBLE_ATOF ("0", VOIDmode))),
+	CONST_DOUBLE_ATOF ("0", DFmode))),
 		gen_rtx_SET (operand0,
 	gen_rtx_NEG (DFmode,
 	copy_rtx (operand1)))));
@@ -1790,7 +1790,7 @@
 	gen_rtx_MULT (DFmode,
 	operand1,
 	operand2),
-	CONST_DOUBLE_ATOF ("0", VOIDmode))),
+	CONST_DOUBLE_ATOF ("0", DFmode))),
 		gen_rtx_SET (operand0,
 	gen_rtx_MULT (DFmode,
 	copy_rtx (operand1),
@@ -1942,7 +1942,7 @@
 	gen_rtx_DIV (DFmode,
 	operand1,
 	operand2),
-	CONST_DOUBLE_ATOF ("0", VOIDmode))),
+	CONST_DOUBLE_ATOF ("0", DFmode))),
 		gen_rtx_SET (operand0,
 	gen_rtx_DIV (DFmode,
 	copy_rtx (operand1),

Provide a new iterator to provide copies of FP substitutions across the
FP modes supported as the substitutions now need to match the mode of
the operands.

	gcc/
	* config/pdp11/pdp11.md (PDPfp): New mode iterator.
	(fcc_cc, fcc_ccnz): Use it.  Add mode to `const_double_zero' and
	operands.