[llvm] [X86] Add MI-layer routine for getting the index of the first address operand. NFC (PR #78019)

[Shengchen Kan via llvm-commits]

================
@@ -3463,6 +3463,44 @@ bool X86::isX87Instruction(MachineInstr &MI) {
   return false;
 }
 
+int X86::getFirstAddrOperandIdx(const MachineInstr &MI) {
+  const auto isMemOp = [](const MCOperandInfo &OpInfo) -> bool {
+    return OpInfo.OperandType == MCOI::OPERAND_MEMORY;
+  };
+
+  const MCInstrDesc &Desc = MI.getDesc();
+
+  // An instruction cannot have a memory reference if it has fewer than
+  // AddrNumOperands (= 5) explicit operands.
+  if (Desc.getNumOperands() < X86::AddrNumOperands) {
+    assert(none_of(Desc.operands(), isMemOp) &&
+           "Expected no operands to have OPERAND_MEMORY type!");
+    return -1;
+  }
+
+  // The first operand with type OPERAND_MEMORY indicates the start of a memory
+  // reference. We expect the following AddrNumOperand-1 operands to also have
+  // OPERAND_MEMORY type.
+  for (unsigned i = 0; i <= Desc.getNumOperands() - X86::AddrNumOperands; ++i) {
+    if (Desc.operands()[i].OperandType == MCOI::OPERAND_MEMORY) {
+      assert(std::all_of(Desc.operands().begin() + i,
+                         Desc.operands().begin() + i + X86::AddrNumOperands,
+                         isMemOp) &&
+             "Expected all five operands in the memory reference to have "
+             "OPERAND_MEMORY type!");
+      return i;
+    }
+  }
+
+  // Fall back to the MC-layer routine, which only handles real (not pseudo)
+  // insturctions.
+  const int FallbackMemOpNo = X86II::getMemoryOperandNo(Desc.TSFlags);
+  if (FallbackMemOpNo >= 0)
+    return FallbackMemOpNo + X86II::getOperandBias(Desc);
+
+  return -1;
+}
----------------
KanRobert wrote:

This implementation has some flaws

1. It increases compile-time for non-pseduo instructions
2. It delays the time when the bug (wrong format) is exposed

Couldn't we can check pseduo and fall back to MC-layer first?


https://github.com/llvm/llvm-project/pull/78019