reapply r103668 with a fix.  Never make "minor syntax changes"
after testing before committing.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103681 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/AsmParser/X86AsmParser.cpp b/lib/Target/X86/AsmParser/X86AsmParser.cpp
index 460410b..2c227b9 100644
--- a/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -622,6 +622,31 @@
   return false;
 }
 
+/// LowerMOffset - Lower an 'moffset' form of an instruction, which just has a
+/// imm operand, to having "rm" or "mr" operands with the offset in the disp
+/// field.
+static void LowerMOffset(MCInst &Inst, unsigned Opc, unsigned RegNo,
+                         bool isMR) {
+  MCOperand Disp = Inst.getOperand(0);
+
+  // Start over with an empty instruction.
+  Inst = MCInst();
+  Inst.setOpcode(Opc);
+  
+  if (!isMR)
+    Inst.addOperand(MCOperand::CreateReg(RegNo));
+  
+  // Add the mem operand.
+  Inst.addOperand(MCOperand::CreateReg(0));  // Segment
+  Inst.addOperand(MCOperand::CreateImm(1));  // Scale
+  Inst.addOperand(MCOperand::CreateReg(0));  // IndexReg
+  Inst.addOperand(Disp);                     // Displacement
+  Inst.addOperand(MCOperand::CreateReg(0));  // BaseReg
+ 
+  if (isMR)
+    Inst.addOperand(MCOperand::CreateReg(RegNo));
+}
+
 // FIXME: Custom X86 cleanup function to implement a temporary hack to handle
 // matching INCL/DECL correctly for x86_64. This needs to be replaced by a
 // proper mechanism for supporting (ambiguous) feature dependent instructions.
@@ -637,6 +662,14 @@
   case X86::INC16m: Inst.setOpcode(X86::INC64_16m); break;
   case X86::INC32r: Inst.setOpcode(X86::INC64_32r); break;
   case X86::INC32m: Inst.setOpcode(X86::INC64_32m); break;
+      
+  // moffset instructions are x86-32 only.
+  case X86::MOV8o8a:   LowerMOffset(Inst, X86::MOV8rm , X86::AL , false); break;
+  case X86::MOV16o16a: LowerMOffset(Inst, X86::MOV16rm, X86::AX , false); break;
+  case X86::MOV32o32a: LowerMOffset(Inst, X86::MOV32rm, X86::EAX, false); break;
+  case X86::MOV8ao8:   LowerMOffset(Inst, X86::MOV8mr , X86::AL , true); break;
+  case X86::MOV16ao16: LowerMOffset(Inst, X86::MOV16mr, X86::AX , true); break;
+  case X86::MOV32ao32: LowerMOffset(Inst, X86::MOV32mr, X86::EAX, true); break;
   }
 }