Add support for "xlat m8"

[myatsina]

Summary

According to x86 spec "xlat m8" is a legal instruction and it is equivalent to "xlatb".

[rnk]

This is another instruction that gas warns on when you don't pass the expected [ebx] operand.

[myatsina]

Added warning regarding the fact that these instructions use (R|E)BX instead of the specified memory operand

[myatsina]

ping

[myatsina]

I've added the warning as you suggested, can you please review the new version?

[rnk]

lgtm

Thanks, just got back from vacation.

llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp

if (Name == "int" && Operands.size() == 2) {
     if (Op1.isImm())
       if (auto *CE = dyn_cast<MCConstantExpr>(Op1.getImm()))
         if (CE->getValue() == 3) {
           Operands.erase(Operands.begin() + 1);
           static_cast<X86Operand &>(*Operands[0]).setTokenValue("int3");
         }
   }
 
+  // Transforms "xlat mem8" into "xlatb"
+  if ((Name == "xlat" || Name == "xlatb") && Operands.size() == 2) {
+    X86Operand &Op1 = static_cast<X86Operand &>(*Operands[1]);
+    if (Op1.isMem8()) {
+      Warning(Op1.getStartLoc(), "memory operand is only for determining the "
+                                 "size, (R|E)BX will be used for the location");
+      Operands.pop_back();
+      static_cast<X86Operand &>(*Operands[0]).setTokenValue("xlatb");
+    }
+  }
+
   return false;
 }
 
 bool X86AsmParser::processInstruction(MCInst &Inst, const OperandVector &Ops) {
   switch (Inst.getOpcode()) {
   default: return false;
   case X86::VMOVZPQILo2PQIrr:
   case X86::VMOVAPDrr:

llvm/trunk/test/MC/X86/intel-syntax.s

 cmps word ptr [eax], word ptr [ebx]
 // CHECK: cmpsw %es:(%edi), (%esi)
 // CHECK-STDERR: memory operand is only for determining the size, ES:(R|E)SI will be used for the location
 // CHECK-STDERR: memory operand is only for determining the size, ES:(R|E)DI will be used for the location
 movs dword ptr [eax], dword ptr [ebx]
 // CHECK: movsl (%esi), %es:(%edi)
 // CHECK-STDERR: memory operand is only for determining the size, ES:(R|E)DI will be used for the location
 // CHECK-STDERR: memory operand is only for determining the size, ES:(R|E)SI will be used for the location
+
+xlat byte ptr [eax]
+// CHECK: xlatb
+// CHECK-STDERR: memory operand is only for determining the size, (R|E)BX will be used for the location