MIR Serialization: Introduce a lexer for machine instructions.

This commit adds a function that tokenizes the string containing
the machine instruction. This commit also adds a struct called 
'MIToken' which is used to represent the lexer's tokens.

Reviewers: Sean Silva

Differential Revision: http://reviews.llvm.org/D10521


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240323 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MIRParser/MILexer.cpp

@@ -0,0 +1,87 @@
+//===- MILexer.cpp - Machine instructions lexer implementation ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the lexing of machine instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "MILexer.h"
+#include "llvm/ADT/Twine.h"
+#include <cctype>
+
+using namespace llvm;
+
+namespace {
+
+/// This class provides a way to iterate and get characters from the source
+/// string.
+class Cursor {
+  const char *Ptr;
+  const char *End;
+
+public:
+  explicit Cursor(StringRef Str) {
+    Ptr = Str.data();
+    End = Ptr + Str.size();
+  }
+
+  bool isEOF() const { return Ptr == End; }
+
+  char peek() const { return isEOF() ? 0 : *Ptr; }
+
+  void advance() { ++Ptr; }
+
+  StringRef remaining() const { return StringRef(Ptr, End - Ptr); }
+
+  StringRef upto(Cursor C) const {
+    assert(C.Ptr >= Ptr && C.Ptr <= End);
+    return StringRef(Ptr, C.Ptr - Ptr);
+  }
+
+  StringRef::iterator location() const { return Ptr; }
+};
+
+} // end anonymous namespace
+
+/// Skip the leading whitespace characters and return the updated cursor.
+static Cursor skipWhitespace(Cursor C) {
+  while (isspace(C.peek()))
+    C.advance();
+  return C;
+}
+
+static bool isIdentifierChar(char C) {
+  return isalpha(C) || isdigit(C) || C == '_' || C == '-' || C == '.';
+}
+
+static Cursor lexIdentifier(Cursor C, MIToken &Token) {
+  auto Range = C;
+  while (isIdentifierChar(C.peek()))
+    C.advance();
+  Token = MIToken(MIToken::Identifier, Range.upto(C));
+  return C;
+}
+
+StringRef llvm::lexMIToken(
+    StringRef Source, MIToken &Token,
+    function_ref<void(StringRef::iterator Loc, const Twine &)> ErrorCallback) {
+  auto C = skipWhitespace(Cursor(Source));
+  if (C.isEOF()) {
+    Token = MIToken(MIToken::Eof, C.remaining());
+    return C.remaining();
+  }
+
+  auto Char = C.peek();
+  if (isalpha(Char) || Char == '_')
+    return lexIdentifier(C, Token).remaining();
+  Token = MIToken(MIToken::Error, C.remaining());
+  ErrorCallback(C.location(),
+                Twine("unexpected character '") + Twine(Char) + "'");
+  return C.remaining();
+}