Use operand->extract to provide defaults for optional PowerPC operands

Most optional operands to powerpc instructions use a default value of
zero, but there are a few exceptions.  Those have been handled by
PPC_OPERAND_OPTIONAL_VALUE and an entry in the powerpc_operands table
for the default value, smuggled in the shift field.  This patch
changes that to using the operand extract function to provide non-zero
defaults.

I've also moved the code determining whether optional operands are
provided or omitted, to the point the first optional operand is seen,
and allowed for the possibility of optional base register operands
in a future patch.

The patch does change the error you get on invalid assembly like

  ld 3,4

You'll now see "missing operand" rather than
"syntax error; end of line, expected `('".

gas/
	* config/tc-ppc.c (md_assemble): Delay counting of optional
	operands until one is encountered.  Allow for the possibility
	of optional base regs, ie. PPC_OPERAND_PARENS.  Call
	ppc_optional_operand_value with extra args.
include/
	* opcode/ppc.h (struct powerpc_operand): Correct "insert" comment.
	Mention use of "extract" function to provide default value.
	(PPC_OPERAND_OPTIONAL_VALUE): Delete.
	(ppc_optional_operand_value): Rewrite to use extract function.
opcodes/
	* ppc-dis.c (operand_value_powerpc): Init "invalid".
	(skip_optional_operands): Count optional operands, and update
	ppc_optional_operand_value call.
	* ppc-opc.c (extract_dxdn): Remove ATTRIBUTE_UNUSED from used arg.
	(extract_vlensi): Likewise.
	(extract_fxm): Return default value for missing optional operand.
	(extract_ls, extract_raq, extract_tbr): Likewise.
	(insert_sxl, extract_sxl): New functions.
	(insert_esync, extract_esync): Remove Power9 handling and simplify.
	(powerpc_operands <FXM4, TBR>): Delete PPC_OPERAND_OPTIONAL_VALUE
	flag and extra entry.
	(powerpc_operands <SXL>): Likewise, and use insert_sxl and
	extract_sxl.

2 files changed, 81 insertions, 78 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index 031fb42..366f4c1 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,5 +1,12 @@
 2018-08-21  Alan Modra  <amodra@gmail.com>
 
+	* config/tc-ppc.c (md_assemble): Delay counting of optional
+	operands until one is encountered.  Allow for the possibility
+	of optional base regs, ie. PPC_OPERAND_PARENS.  Call
+	ppc_optional_operand_value with extra args.
+
+2018-08-21  Alan Modra  <amodra@gmail.com>
+
 	* testsuite/gas/s12z/bit-manip-invalid.d: Correct regexps.
 
 2018-08-18  John Darrington  <john@darrington.wattle.id.au>
diff --git a/gas/config/tc-ppc.c b/gas/config/tc-ppc.c
index 6135cb4..d4cc2ff 100644
--- a/gas/config/tc-ppc.c
+++ b/gas/config/tc-ppc.c
@@ -2745,7 +2745,6 @@ md_assemble (char *str)
   const struct powerpc_opcode *opcode;
   uint64_t insn;
   const unsigned char *opindex_ptr;
-  int skip_optional;
   int need_paren;
   int next_opindex;
   struct ppc_fixup fixups[MAX_INSN_FIXUPS];
@@ -2783,55 +2782,11 @@ md_assemble (char *str)
     ++str;
 
   /* PowerPC operands are just expressions.  The only real issue is
-     that a few operand types are optional.  All cases which might use
-     an optional operand separate the operands only with commas (in some
-     cases parentheses are used, as in ``lwz 1,0(1)'' but such cases never
-     have optional operands).  Most instructions with optional operands
-     have only one.  Those that have more than one optional operand can
-     take either all their operands or none.  So, before we start seriously
-     parsing the operands, we check to see if we have optional operands,
-     and if we do, we count the number of commas to see which operands
-     have been omitted.  */
-  skip_optional = 0;
-  for (opindex_ptr = opcode->operands; *opindex_ptr != 0; opindex_ptr++)
-    {
-      const struct powerpc_operand *operand;
-
-      operand = &powerpc_operands[*opindex_ptr];
-      if ((operand->flags & PPC_OPERAND_OPTIONAL) != 0
-	  && !((operand->flags & PPC_OPERAND_OPTIONAL32) != 0 && ppc_obj64))
-	{
-	  unsigned int opcount;
-	  unsigned int num_operands_expected;
-
-	  /* There is an optional operand.  Count the number of
-	     commas in the input line.  */
-	  if (*str == '\0')
-	    opcount = 0;
-	  else
-	    {
-	      opcount = 1;
-	      s = str;
-	      while ((s = strchr (s, ',')) != (char *) NULL)
-		{
-		  ++opcount;
-		  ++s;
-		}
-	    }
-
-	  /* Compute the number of expected operands.  */
-	  for (num_operands_expected = 0, i = 0; opcode->operands[i]; i ++)
-	    ++ num_operands_expected;
-
-	  /* If there are fewer operands in the line then are called
-	     for by the instruction, we want to skip the optional
-	     operands.  */
-	  if (opcount < num_operands_expected)
-	    skip_optional = 1;
-
-	  break;
-	}
-    }
+     that a few operand types are optional.  If an instruction has
+     multiple optional operands and one is omitted, then all optional
+     operands past the first omitted one must also be omitted.  */
+  int num_optional_operands = 0;
+  int num_optional_provided = 0;
 
   /* Gather the operands.  */
   need_paren = 0;
@@ -2855,26 +2810,66 @@ md_assemble (char *str)
       errmsg = NULL;
 
       /* If this is an optional operand, and we are skipping it, just
-	 insert a zero.  */
+	 insert the default value, usually a zero.  */
       if ((operand->flags & PPC_OPERAND_OPTIONAL) != 0
-	  && !((operand->flags & PPC_OPERAND_OPTIONAL32) != 0 && ppc_obj64)
-	  && skip_optional)
+	  && !((operand->flags & PPC_OPERAND_OPTIONAL32) != 0 && ppc_obj64))
 	{
-	  int64_t val = ppc_optional_operand_value (operand);
-	  if (operand->insert)
+	  if (num_optional_operands == 0)
 	    {
-	      insn = (*operand->insert) (insn, val, ppc_cpu, &errmsg);
-	      if (errmsg != (const char *) NULL)
-		as_bad ("%s", errmsg);
+	      const unsigned char *optr;
+	      int total = 0;
+	      int provided = 0;
+	      int omitted;
+
+	      s = str;
+	      for (optr = opindex_ptr; *optr != 0; optr++)
+		{
+		  const struct powerpc_operand *op;
+		  op = &powerpc_operands[*optr];
+
+		  ++total;
+
+		  if ((op->flags & PPC_OPERAND_OPTIONAL) != 0
+		      && !((op->flags & PPC_OPERAND_OPTIONAL32) != 0
+			   && ppc_obj64))
+		    ++num_optional_operands;
+
+		  if (s != NULL && *s != '\0')
+		    {
+		      ++provided;
+
+		      /* Look for the start of the next operand.  */
+		      if ((op->flags & PPC_OPERAND_PARENS) != 0)
+			s = strpbrk (s, "(,");
+		      else
+			s = strchr (s, ',');
+
+		      if (s != NULL)
+			++s;
+		    }
+		}
+	      omitted = total - provided;
+	      num_optional_provided = num_optional_operands - omitted;
 	    }
-	  else if (operand->shift >= 0)
-	    insn |= (val & operand->bitm) << operand->shift;
-	  else
-	    insn |= (val & operand->bitm) >> -operand->shift;
+	  if (--num_optional_provided < 0)
+	    {
+	      int64_t val = ppc_optional_operand_value (operand, insn, ppc_cpu,
+							num_optional_provided);
+	      if (operand->insert)
+		{
+		  insn = (*operand->insert) (insn, val, ppc_cpu, &errmsg);
+		  if (errmsg != (const char *) NULL)
+		    as_bad ("%s", errmsg);
+		}
+	      else if (operand->shift >= 0)
+		insn |= (val & operand->bitm) << operand->shift;
+	      else
+		insn |= (val & operand->bitm) >> -operand->shift;
 
-	  if ((operand->flags & PPC_OPERAND_NEXT) != 0)
-	    next_opindex = *opindex_ptr + 1;
-	  continue;
+	      if ((operand->flags & PPC_OPERAND_NEXT) != 0)
+		next_opindex = *opindex_ptr + 1;
+	      continue;
+	    }
 	}
 
       /* Gather the operand.  */
@@ -3448,27 +3443,28 @@ md_assemble (char *str)
 	    }
 	}
       else if ((operand->flags & PPC_OPERAND_PARENS) != 0)
-	{
-	  endc = '(';
-	  need_paren = 1;
-	}
+	endc = '(';
       else
 	endc = ',';
 
       /* The call to expression should have advanced str past any
 	 whitespace.  */
-      if (*str != endc
-	  && (endc != ',' || *str != '\0'))
+      if (*str == endc)
 	{
-	  if (*str == '\0')
-	    as_bad (_("syntax error; end of line, expected `%c'"), endc);
-	  else
-	    as_bad (_("syntax error; found `%c', expected `%c'"), *str, endc);
+	  ++str;
+	  if (endc == '(')
+	    need_paren = 1;
+	}
+      else if (*str != '\0')
+	{
+	  as_bad (_("syntax error; found `%c', expected `%c'"), *str, endc);
+	  break;
+	}
+      else if (endc == ')')
+	{
+	  as_bad (_("syntax error; end of line, expected `%c'"), endc);
 	  break;
 	}
-
-      if (*str != '\0')
-	++str;
     }
 
   while (ISSPACE (*str))