"sldt <mem>" is ambiguous in 64-bit mode, but should

always be disambiguated as sldtw.  sldtw and sldtq with
a mem operands have the same effect, but sldtw is more
compact.  Force it to sldtw, resolving rdar://8017530


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@113186 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/AsmParser/X86AsmParser.cpp

@@ -820,6 +820,13 @@ ParseInstruction(StringRef Name, SMLoc NameLoc,
                                              Op->getEndLoc()));
   }
   
+  // 'sldt <mem>' can be encoded with either sldtw or sldtq with the same
+  // effect (both store to a 16-bit mem).  Force to sldtw to avoid ambiguity
+  // errors, since its encoding is the most compact.
+  if (Name == "sldt" && Operands.size() == 2 &&
+      static_cast<X86Operand*>(Operands[1])->isMem())
+    Operands[0] = X86Operand::CreateToken("sldtw", NameLoc);
+
   return false;
 }
 

test/MC/AsmParser/X86/x86_instructions.s

@@ -178,3 +178,6 @@ inb	$161, %al
 // CHECK: pushq	$1
 push $1
 
+// rdar://8017530
+// CHECK: sldtw	4
+sldt	4