[X86][MC] Support encoding/decoding for PUSH2[P]/POP2[P] (#73233)

PUSH2 and POP2 are two new instructions for (respectively)
pushing/popping 2 GPRs at a time to/from
the stack. The opcodes of PUSH2 and POP2 are those of “PUSH r/m” and
“POP r/m” from legacy map 0, but we
require ModRM.Mod = 3 in order to disallow memory operand. 

The 1-bit Push-Pop Acceleration hint described in #73092 applies to
PUSH2/POP2 too, then we have PUSH2P/POP2P.

For AT&T syntax, PUSH2[P] pushes the registers from right to left onto
the stack. POP2[P] pops the stack to registers from right to left. Intel
syntax has the opposite order - from left to right.

The assembly syntax is aligned with GCC & binutils
https://gcc.gnu.org/pipermail/gcc-patches/2023-November/637718.html

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
index d5218d3..d50e651 100644
--- a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
+++ b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
@@ -150,6 +150,9 @@ static InstrUID decode(OpcodeType type, InstructionContext insnContext,
     dec =
         &THREEDNOW_MAP_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
     break;
+  case MAP4:
+    dec = &MAP4_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
+    break;
   case MAP5:
     dec = &MAP5_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
     break;
@@ -929,6 +932,9 @@ static bool readOpcode(struct InternalInstruction *insn) {
     case VEX_LOB_0F3A:
       insn->opcodeType = THREEBYTE_3A;
       return consume(insn, insn->opcode);
+    case VEX_LOB_MAP4:
+      insn->opcodeType = MAP4;
+      return consume(insn, insn->opcode);
     case VEX_LOB_MAP5:
       insn->opcodeType = MAP5;
       return consume(insn, insn->opcode);
@@ -1100,6 +1106,9 @@ static int getInstructionIDWithAttrMask(uint16_t *instructionID,
   case THREEDNOW_MAP:
     decision = &THREEDNOW_MAP_SYM;
     break;
+  case MAP4:
+    decision = &MAP4_SYM;
+    break;
   case MAP5:
     decision = &MAP5_SYM;
     break;