Do not allow ASCII literals to be parsed

llvm/lib/MC/MCParser/AsmParser.cpp

if (Lexer.is(AsmToken::Error))
     return TokError(Lexer.getErr());
   if (Lexer.isNot(AsmToken::Integer) && Lexer.isNot(AsmToken::Real) &&
       Lexer.isNot(AsmToken::Identifier))
     return TokError("unexpected token in directive");
 
   // Convert to an APFloat.
   APFloat Value(Semantics);
   StringRef IDVal = getTok().getString();
+
+  // We do not currently handle ASCII literals e.g. 't' = 116
+  if(getLexer().is(AsmToken::Integer) && IDVal.startswith("'")){
+    return TokError("ASCII literal not supported");
+  }
+
   if (getLexer().is(AsmToken::Identifier)) {
     if (!IDVal.compare_lower("infinity") || !IDVal.compare_lower("inf"))
       Value = APFloat::getInf(Semantics);
     else if (!IDVal.compare_lower("nan"))
       Value = APFloat::getNaN(Semantics, false, ~0);
     else
       return TokError("invalid floating point literal");
   } else if (Value.convertFromString(IDVal, APFloat::rmNearestTiesToEven) ==

llvm/test/MC/AsmParser/floating-literals.s

 # CHECK: .quad  4591870180066957722
 .double 1E-1
 
 
 #CHECK-ERROR: unexpected token in '.double' directive
 .double 1e1e
 # CHECK-ERROR: Invalid sign in float literal
 .double 2.+1
+#CHECK-ERROR: error: ASCII literal not supported in '.double' directive
+.double 't'
 
 # CHECK: .long 1310177520
 .float 0x12f7.1ep+17
 # CHECK: .long 1084227584
 .float 0x.ap+3
 # CHECK: .quad 4602678819172646912
 .double 0x2.p-2
 # CHECK: .long 1094713344