[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, 4 insertions, 3 deletions

diff --git a/llvm/utils/TableGen/X86DisassemblerTables.cpp b/llvm/utils/TableGen/X86DisassemblerTables.cpp
index e8dffaa..f879a9f 100644
--- a/llvm/utils/TableGen/X86DisassemblerTables.cpp
+++ b/llvm/utils/TableGen/X86DisassemblerTables.cpp
@@ -983,9 +983,10 @@ void DisassemblerTables::emitContextDecisions(raw_ostream &o1, raw_ostream &o2,
   emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[5], XOP9_MAP_STR);
   emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[6], XOPA_MAP_STR);
   emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[7], THREEDNOW_MAP_STR);
-  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[8], MAP5_STR);
-  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[9], MAP6_STR);
-  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[10], MAP7_STR);
+  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[8], MAP4_STR);
+  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[9], MAP5_STR);
+  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[10], MAP6_STR);
+  emitContextDecision(o1, o2, i1, i2, ModRMTableNum, *Tables[11], MAP7_STR);
 }
 
 void DisassemblerTables::emit(raw_ostream &o) const {