RISC-V: Non-standard encodings of `fence' (disasm)

This commit adds disassembler support for non-standard encodings of the
`fence' instruction.  Despite that those fields are reserved in many
cases, base implementation shall ignore and handle with fm=0000.

gas/ChangeLog:

	* config/tc-riscv.c (validate_riscv_insn): Add ignored fm field.
	(riscv_ip): Add ignored fm field.
	* testsuite/gas/riscv/fence-dis-nonstd.s: New disasm test.
	* testsuite/gas/riscv/fence-dis-nonstd.d: Likewise.

include/ChangeLog:

	* opcode/riscv.h (OP_MASK_FM, OP_SH_FM): New.

opcodes/ChangeLog:

	* riscv-dis.c (print_insn_args): Add ignored fm field.
	* riscv-opc.c (riscv_opcodes): Reorder `fence.tso' so that reserved
	`fence' instruction entry is matched at the end.  Ignore reserved
	bit positions.

gas/config/tc-riscv.c

@@ -1261,6 +1261,8 @@ validate_riscv_insn (const struct riscv_opcode *opc, int length)
 		case 'd': USE_BITS (OP_MASK_RD, OP_SH_RD); break;
 		case 's': USE_BITS (OP_MASK_RS1, OP_SH_RS1); break;
 		case 'j': used_bits |= ENCODE_ITYPE_IMM (-1U); break;
+		/* fence: fm field.  */
+		case 'f': USE_BITS (OP_MASK_FM, OP_SH_FM); break;
 		default:
 		  goto unknown_validate_operand;
 		}
@@ -3296,6 +3298,7 @@ riscv_ip (char *str, struct riscv_cl_insn *ip, expressionS *imm_expr,
 		    case 'd': /* Ignored RD.  */
 		    case 's': /* Ignored RS1.  */
 		    case 'j': /* Ignored immediate (I-type).  */
+		    case 'f': /* Ignored fence fm field.  */
 		      break;
 		    default:
 		      goto unknown_riscv_ip_operand;

gas/testsuite/gas/riscv/fence-dis-nonstd.d

@@ -0,0 +1,20 @@
+#as: -march=rv32i
+#source: fence-dis-nonstd.s
+#objdump: -dr
+
+.*:[ 	]+file format .*
+
+
+Disassembly of section .text:
+
+0+000 <target>:
+[ 	]+[0-9a-f]+:[ 	]+0ff0000f[ 	]+fence
+[ 	]+[0-9a-f]+:[ 	]+8330000f[ 	]+fence\.tso
+[ 	]+[0-9a-f]+:[ 	]+0ff0000f[ 	]+fence
+[ 	]+[0-9a-f]+:[ 	]+8330000f[ 	]+fence\.tso
+[ 	]+[0-9a-f]+:[ 	]+0cf00f8f[ 	]+fence[ 	]+io,iorw
+[ 	]+[0-9a-f]+:[ 	]+0fcf800f[ 	]+fence[ 	]+iorw,io
+[ 	]+[0-9a-f]+:[ 	]+83300f8f[ 	]+fence\.tso
+[ 	]+[0-9a-f]+:[ 	]+833f800f[ 	]+fence\.tso
+[ 	]+[0-9a-f]+:[ 	]+8ff0000f[ 	]+fence[ 	]+iorw,iorw
+[ 	]+[0-9a-f]+:[ 	]+1330000f[ 	]+fence[ 	]+rw,rw

gas/testsuite/gas/riscv/fence-dis-nonstd.s

@@ -0,0 +1,20 @@
+target:
+	fence
+	fence.tso
+	# Standard encodings of fence and fence.tso
+	.insn i	MISC_MEM, 0,  x0,  x0,  0x0ff
+	.insn i	MISC_MEM, 0,  x0,  x0,  0x833-0x1000
+	# Non-standard encodings (regular, either RD or RS1 are non-zero)
+	# Ignore unused bit fields.
+	.insn i	MISC_MEM, 0, x31,  x0,  0x0cf
+	.insn i	MISC_MEM, 0,  x0, x31,  0x0fc
+	# Non-standard encodings (TSO, either RD or RS1 are non-zero)
+	# Ignore unused bit fields for fence.tso.
+	.insn i	MISC_MEM, 0, x31,  x0,  0x833-0x1000
+	.insn i	MISC_MEM, 0,  x0, x31,  0x833-0x1000
+	# Non-standard encoding (TSO, pred and succ are not defined)
+	# Since fm+pred+succ is not defined, fallback to regular fence.
+	.insn i	MISC_MEM, 0,  x0,  x0,  0x8ff-0x1000
+	# Non-standard encoding (fm is reserved)
+	# Fallback to regular fence.
+	.insn i	MISC_MEM, 0,  x0,  x0,  0x133

include/opcode/riscv.h

@@ -245,6 +245,8 @@ static const char * const riscv_pred_succ[16] =
 #define OP_SH_AQ		26
 #define OP_MASK_RL		0x1
 #define OP_SH_RL		25
+#define OP_MASK_FM		0xfU
+#define OP_SH_FM		28
 
 #define OP_MASK_CSR		0xfffU
 #define OP_SH_CSR		20

opcodes/riscv-opc.c

@@ -418,10 +418,10 @@ const struct riscv_opcode riscv_opcodes[] =
 {"sw",          0, INSN_CLASS_I, "t,q(s)",    MATCH_SW, MASK_SW, match_opcode, INSN_DREF|INSN_4_BYTE },
 {"sw",          0, INSN_CLASS_I, "t,A,s",     0, (int) M_SW, match_never, INSN_MACRO },
 {"pause",       0, INSN_CLASS_ZIHINTPAUSE, "",MATCH_PAUSE, MASK_PAUSE, match_opcode, 0 },
+{"fence.tso",   0, INSN_CLASS_I, "~ds",       MATCH_FENCE_TSO, MASK_FENCE_TSO, match_opcode, 0 },
 {"fence",       0, INSN_CLASS_I, "",          MATCH_FENCE|MASK_PRED|MASK_SUCC, MASK_FENCE|MASK_RD|MASK_RS1|MASK_IMM, match_opcode, INSN_ALIAS },
-{"fence",       0, INSN_CLASS_I, "P,Q",       MATCH_FENCE, MASK_FENCE|MASK_RD|MASK_RS1|(MASK_IMM & ~MASK_PRED & ~MASK_SUCC), match_opcode, 0 },
+{"fence",       0, INSN_CLASS_I, "P,Q~dsf",   MATCH_FENCE, MASK_FENCE, match_opcode, 0 },
 {"fence.i",     0, INSN_CLASS_ZIFENCEI, "~dsj", MATCH_FENCE_I, MASK_FENCE_I, match_opcode, 0 },
-{"fence.tso",   0, INSN_CLASS_I, "",          MATCH_FENCE_TSO, MASK_FENCE_TSO|MASK_RD|MASK_RS1, match_opcode, INSN_ALIAS },
 {"rdcycle",     0, INSN_CLASS_I, "d",         MATCH_RDCYCLE, MASK_RDCYCLE, match_opcode, INSN_ALIAS },
 {"rdinstret",   0, INSN_CLASS_I, "d",         MATCH_RDINSTRET, MASK_RDINSTRET, match_opcode, INSN_ALIAS },
 {"rdtime",      0, INSN_CLASS_I, "d",         MATCH_RDTIME, MASK_RDTIME, match_opcode, INSN_ALIAS },