Revert r373888 "[IA] Recognize hexadecimal escape sequences"

It broke MC/AsmParser/directive_ascii.s on all bots:

    Assertion failed: (Index < Length && "Invalid index!"), function operator[],
        file ../../llvm/include/llvm/ADT/StringRef.h, line 243.

llvm-svn: 373898

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -2914,26 +2914,11 @@ bool AsmParser::parseEscapedString(std::string &Data) {
     }
 
     // Recognize escaped characters. Note that this escape semantics currently
-    // loosely follows Darwin 'as'.
+    // loosely follows Darwin 'as'. Notably, it doesn't support hex escapes.
     ++i;
     if (i == e)
       return TokError("unexpected backslash at end of string");
 
-    // Recognize hex sequences similarly to GNU 'as'.
-    if (Str[i] == 'x' || Str[i] == 'X') {
-      if (!isHexDigit(Str[i + 1]))
-        return TokError("invalid hexadecimal escape sequence");
-
-      // Consume hex characters. GNU 'as' reads all hexadecimal characters and
-      // then truncates to the lower 16 bits. Seems reasonable.
-      unsigned Value = 0;
-      while (isHexDigit(Str[i + 1]))
-        Value = Value * 16 + hexDigitValue(Str[++i]);
-
-      Data += (unsigned char)(Value & 0xFF);
-      continue;
-    }
-
     // Recognize octal sequences.
     if ((unsigned)(Str[i] - '0') <= 7) {
       // Consume up to three octal characters.

llvm/test/MC/AsmParser/directive_ascii.s

@@ -39,8 +39,3 @@ TEST5:
 # CHECK: .byte 0
 TEST6:
         .string "B", "C"
-
-# CHECK: TEST7:
-# CHECK: .ascii "dk"
-TEST7:
-        .ascii "\x64\Xa6B"