Allow for optional operands with non-zero default values.

ISA 2.07 (ie, POWER8) added the rfebb instruction which takes one operand
with the value of either a 0 or 1.  It also defines an extended mnemonic
with no operands (ie, "rfebb") that is supposed to be equivalent to "rfebb 1".
I implemented rfebb's lone operand with PPC_OPERAND_OPTIONAL, but the
problem is, optional operands that are ommitted always default to the
value 0, which is wrong in this case.  I have added support for allowing
non-zero default values by adding an additional flag PPC_OPERAND_OPTIONAL_VALUE
that specifies that the default operand value to be used is stored in the
SHIFT field of the operand field immediately following this one.

This fixes the rfebb issue.  I also fixed the mftb and mfcr instructions
so they use the same mechanism.  This allows us to flag invalid uses of
mfcr where we explicitly pass in a zero FXM value, like the use in a2.[sd].

include/opcode/

	* ppc.h (PPC_OPERAND_OPTIONAL_VALUE): New.
	(ppc_optional_operand_value): New inline function.

opcodes/
	* ppc-dis.h (skip_optional_operands): Use ppc_optional_operand_value.
	* ppc-opc.c (FXM4): Add non-zero optional value.
	(TBR): Likewise.
	(SXL): Likewise.
	(insert_fxm): Handle new default operand value.
	(extract_fxm): Likewise.
	(insert_tbr): Likewise.
	(extract_tbr): Likewise.

gas/
	* config/tc-ppc.c (md_assemble): Use ppc_optional_operand_value.
	Allow for optional operands without insert functions.

gas/testsuite/
	* gas/ppc/power8.d: Fixup rfebb test results.
	* gas/ppc/a2.s: Fix invalid mfcr test.
	* gas/ppc/a2.d: Likewise.

1 files changed, 7 insertions, 1 deletions

diff --git a/gas/config/tc-ppc.c b/gas/config/tc-ppc.c
index 3f6de73..18a11be 100644
--- a/gas/config/tc-ppc.c
+++ b/gas/config/tc-ppc.c
@@ -2752,12 +2752,18 @@ md_assemble (char *str)
       if ((operand->flags & PPC_OPERAND_OPTIONAL) != 0
 	  && skip_optional)
 	{
+	  long val = ppc_optional_operand_value (operand);
 	  if (operand->insert)
 	    {
-	      insn = (*operand->insert) (insn, 0L, ppc_cpu, &errmsg);
+	      insn = (*operand->insert) (insn, val, ppc_cpu, &errmsg);
 	      if (errmsg != (const char *) NULL)
 		as_bad ("%s", errmsg);
 	    }
+	  else if (operand->shift >= 0)
+	    insn |= ((long) val & operand->bitm) << operand->shift;
+	  else
+	    insn |= ((long) val & operand->bitm) >> -operand->shift;
+
 	  if ((operand->flags & PPC_OPERAND_NEXT) != 0)
 	    next_opindex = *opindex_ptr + 1;
 	  continue;