[PATCH] gas/RISC-V: adjust assembler for opcode table re-ordering

[Jan Beulich <jbeulich@suse.com>]

PR gas/29940

With the single-operand JAL entry now sitting ahead of the two-operand
one, the parsing of a two-operand insn would first try to parse an 'a'-
style operand, resulting in the insertion of bogus (and otherwise
unused) undefined symbols in the symbol table, having register names.
Since 'a' is used as 1st operand only with J and JAL, and since JAL is
the only insn _also_ allowing for a register as 1st operand (and then
there being a 2nd one), special case this parsing aspect right there.
---
This, of course, is fragile, but I guess such workarounds are
unavoidable with the chosen approach of (recurring) parsing, and with
register names being special only in certain contexts.

A more generic approach, then possibly also helping performance, might
be to count the number of operands first, and do full parsing only when
the count matches that in the operand specifier string (at least when
there are multiple insn forms).

The similar workaround in my_getSmallExpression() actually looks
suspicious to me: I expect that it would get in the way of using equates
"shadowing" names of GPRs.

--- a/gas/config/tc-riscv.c
+++ b/gas/config/tc-riscv.c
@@ -3266,6 +3266,17 @@ riscv_ip (char *str, struct riscv_cl_ins
 	      continue;
 
 	    case 'a': /* 20-bit PC-relative offset.  */
+	      /* Like in my_getSmallExpression() we need to avoid emitting
+		 a stray undefined symbol if the 1st JAL entry doesn't match,
+		 but the 2nd (with 2 operands) might.  */
+	      if (oparg == insn->args)
+		{
+		  asargStart = asarg;
+		  if (reg_lookup (&asarg, RCLASS_GPR, NULL)
+		      && (*asarg == ',' || (ISSPACE (*asarg) && asarg[1] == ',')))
+		    break;
+		  asarg = asargStart;
+		}
 	    jump:
 	      my_getExpression (imm_expr, asarg);
 	      asarg = expr_end;