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

[Shengchen Kan via llvm-commits]

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@@ -3463,6 +3463,50 @@ 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();
+
+  // Directly invoke the MC-layer routine for real (i.e., non-pseudo)
+  // instructions (fast case).
+  if (!X86II::isPseudo(Desc.TSFlags)) {
+    int MemRefIdx = X86II::getMemoryOperandNo(Desc.TSFlags);
+    if (MemRefIdx >= 0)
+      return MemRefIdx + X86II::getOperandBias(Desc);
+    assert(none_of(Desc.operands(), isMemOp) &&
+           "Got false negative from X86II::getMemoryOperandNo()!");
+    return -1;
+  }
+
+  // Otherwise, handle pseudo instructions by examining the type of their
+  // operands (slow case). 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!");
----------------
KanRobert wrote:

Wrap these in 

#ifdef EXPENSIVE_CHECKS
#endif

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