[X86] A fix for pr35741 - can't use comments with instr prefixes

[avt77]

Summary

After general commit covering several issues with x86 prefixes we lost a possibility to use comments if there is a prefix on a dedicated line. This tiny patch fixes this issue.

[RKSimon]

LGTM

[dim]

Works for me too.

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

unsigned Prefix =
         StringSwitch<unsigned>(Name)
             .Cases("lock", "lock", X86::IP_HAS_LOCK)
             .Cases("rep", "repe", "repz", X86::IP_HAS_REPEAT)
             .Cases("repne", "repnz", X86::IP_HAS_REPEAT_NE)
             .Default(X86::IP_NO_PREFIX); // Invalid prefix (impossible)
     Flags |= Prefix;
     Name = Parser.getTok().getString();
     Parser.Lex(); // eat the prefix
-    // Hack: we could have something like
+    // Hack: we could have something like "rep # some comment" or
     //    "lock; cmpxchg16b $1" or "lock\0A\09incl" or "lock/incl"
     while (Name.startswith(";") || Name.startswith("\n") ||
-           Name.startswith("\t") || Name.startswith("/")) {
+           Name.startswith("#") || Name.startswith("\t") ||
+           Name.startswith("/")) {
       Name = Parser.getTok().getString();
       Parser.Lex(); // go to next prefix or instr
     }
   }
 
   if (Flags)
     PatchedName = Name;
   Operands.push_back(X86Operand::CreateToken(PatchedName, NameLoc));

llvm/trunk/test/MC/X86/x86-64.s

// CHECK: shldl %cl, %eax, %ebx
         shldl %cl, %eax, %ebx
 
 // CHECK: shll $2, %eax
         shll $2, %eax
 
 // CHECK: shll $2, %eax
         sall $2, %eax
 
+// CHECK: rep movsb
+rep     # comment
+movsb
+
 // CHECK: rep
 // CHECK: insb
         rep;insb
 
 // CHECK: rep
 // CHECK: outsb
         rep;outsb