[docs] Update outdated ExtendingLLVM.rst

[chilledheart]

Summary

The document is still incomplete in some degrees, but updated to reflect the
latest changes. Anyway we can detail it if any one think it is not enough. For
the sake of it, some useful examples are listed below:

Refer to r113618 "Add X86 MMX type to bitcode and Type" for how to add a new
type.

One notable change from then is only one thing that `lib/VMCore` is renamed

to `lib/IR`.

Refer to r194760 "Add addrspacecast instruction" for how to add a new
instruction.

[echristo]

I think this looks fine. Thanks!

-eric

[chilledheart]

Hi eric:

I don't have the right to commit this change, could you do it on behalf of me?

Thank you.

[dblaikie]

Committed in r234757

llvm/trunk/docs/ExtendingLLVM.rst

 ========================
 
 .. warning::
 
   Adding instructions changes the bitcode format, and it will take some effort
   to maintain compatibility with the previous version. Only add an instruction
   if it is absolutely necessary.
 
-#. ``llvm/include/llvm/Instruction.def``:
+#. ``llvm/include/llvm/IR/Instruction.def``:
 
    add a number for your instruction and an enum name
 
-#. ``llvm/include/llvm/Instructions.h``:
+#. ``llvm/include/llvm/IR/Instructions.h``:
 
    add a definition for the class that will represent your instruction
 
-#. ``llvm/include/llvm/Support/InstVisitor.h``:
+#. ``llvm/include/llvm/IR/InstVisitor.h``:
 
    add a prototype for a visitor to your new instruction type
 
-#. ``llvm/lib/AsmParser/Lexer.l``:
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
 
    add a new token to parse your instruction from assembly text file
 
-#. ``llvm/lib/AsmParser/llvmAsmParser.y``:
+#. ``llvm/lib/AsmParser/LLParser.cpp``:
 
    add the grammar on how your instruction can be read and what it will
    construct as a result
 
-#. ``llvm/lib/Bitcode/Reader/Reader.cpp``:
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
 
    add a case for your instruction and how it will be parsed from bitcode
 
-#. ``llvm/lib/VMCore/Instruction.cpp``:
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
+
+   add a case for your instruction and how it will be parsed from bitcode
+
+#. ``llvm/lib/IR/Instruction.cpp``:
 
    add a case for how your instruction will be printed out to assembly
 
-#. ``llvm/lib/VMCore/Instructions.cpp``:
+#. ``llvm/lib/IR/Instructions.cpp``:
 
    implement the class you defined in ``llvm/include/llvm/Instructions.h``
 
 #. Test your instruction
 
-#. ``llvm/lib/Target/*``: 
+#. ``llvm/lib/Target/*``:
 
    add support for your instruction to code generators, or add a lowering pass.
 
 #. ``llvm/test/*``:
 
    add your test cases to the test suite.
 
 Also, you need to implement (or modify) any analyses or passes that you want to
 understand this new instruction.
 
 Adding a new type
 =================
 
 .. warning::
 
   Adding new types changes the bitcode format, and will break compatibility with
   currently-existing LLVM installations. Only add new types if it is absolutely
   necessary.
 
 Adding a fundamental type
 -------------------------
 
-#. ``llvm/include/llvm/Type.h``:
+#. ``llvm/include/llvm/IR/Type.h``:
 
    add enum for the new type; add static ``Type*`` for this type
 
-#. ``llvm/lib/VMCore/Type.cpp``:
+#. ``llvm/lib/IR/Type.cpp`` and ``llvm/lib/IR/ValueTypes.cpp``:
 
    add mapping from ``TypeID`` => ``Type*``; initialize the static ``Type*``
 
-#. ``llvm/lib/AsmReader/Lexer.l``:
+#. ``llvm/llvm/llvm-c/Core.cpp``:
+
+   add enum ``LLVMTypeKind`` and modify
+   ``LLVMTypeKind LLVMGetTypeKind(LLVMTypeRef Ty)`` for the new type
+
+#. ``llvm/include/llvm/IR/TypeBuilder.h``:
+
+   add new class to represent new type in the hierarchy
+
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
 
    add ability to parse in the type from text assembly
 
-#. ``llvm/lib/AsmReader/llvmAsmParser.y``:
+#. ``llvm/lib/AsmParser/LLParser.cpp``:
 
    add a token for that type
 
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
+
+   modify ``static void WriteTypeTable(const ValueEnumerator &VE,
+   BitstreamWriter &Stream)`` to serialize your type
+
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
+
+   modify ``bool BitcodeReader::ParseTypeType()`` to read your data type
+
+#. ``include/llvm/Bitcode/LLVMBitCodes.h``:
+
+   add enum ``TypeCodes`` for the new type
+
 Adding a derived type
 ---------------------
 
-#. ``llvm/include/llvm/Type.h``:
+#. ``llvm/include/llvm/IR/Type.h``:
 
    add enum for the new type; add a forward declaration of the type also
 
-#. ``llvm/include/llvm/DerivedTypes.h``:
+#. ``llvm/include/llvm/IR/DerivedTypes.h``:
 
    add new class to represent new class in the hierarchy; add forward
    declaration to the TypeMap value type
 
-#. ``llvm/lib/VMCore/Type.cpp``:
+#. ``llvm/lib/IR/Type.cpp`` and ``llvm/lib/IR/ValueTypes.cpp``:
 
-   add support for derived type to:
+   add support for derived type, notably `enum TypeID` and `is`, `get` methods.
 
-   .. code-block:: c++
+#. ``llvm/llvm/llvm-c/Core.cpp``:
 
-     std::string getTypeDescription(const Type &Ty,
-                                    std::vector<const Type*> &TypeStack)
-     bool TypesEqual(const Type *Ty, const Type *Ty2,
-                     std::map<const Type*, const Type*> &EqTypes)
+   add enum ``LLVMTypeKind`` and modify
+   `LLVMTypeKind LLVMGetTypeKind(LLVMTypeRef Ty)` for the new type
 
-   add necessary member functions for type, and factory methods
+#. ``llvm/include/llvm/IR/TypeBuilder.h``:
 
-#. ``llvm/lib/AsmReader/Lexer.l``:
+   add new class to represent new class in the hierarchy
 
-   add ability to parse in the type from text assembly
+#. ``llvm/lib/AsmParser/LLLexer.cpp``:
 
-#. ``llvm/lib/Bitcode/Writer/Writer.cpp``:
+   modify ``lltok::Kind LLLexer::LexIdentifier()`` to add ability to
+   parse in the type from text assembly
 
-   modify ``void BitcodeWriter::outputType(const Type *T)`` to serialize your
-   type
+#. ``llvm/lib/Bitcode/Writer/BitcodeWriter.cpp``:
 
-#. ``llvm/lib/Bitcode/Reader/Reader.cpp``:
+   modify ``static void WriteTypeTable(const ValueEnumerator &VE,
+   BitstreamWriter &Stream)`` to serialize your type
 
-   modify ``const Type *BitcodeReader::ParseType()`` to read your data type
+#. ``llvm/lib/Bitcode/Reader/BitcodeReader.cpp``:
 
-#. ``llvm/lib/VMCore/AsmWriter.cpp``:
+   modify ``bool BitcodeReader::ParseTypeType()`` to read your data type
 
-   modify
+#. ``include/llvm/Bitcode/LLVMBitCodes.h``:
 
-   .. code-block:: c++
+   add enum ``TypeCodes`` for the new type
 
-     void calcTypeName(const Type *Ty,
-                       std::vector<const Type*> &TypeStack,
-                       std::map<const Type*,std::string> &TypeNames,
-                       std::string &Result)
+#. ``llvm/lib/IR/AsmWriter.cpp``:
 
+   modify ``void TypePrinting::print(Type *Ty, raw_ostream &OS)``
    to output the new derived type