[Orc][Kaleidoscope] Add an example of extreme-laziness in Orc.

The version of the tutorial uses the new compile callbacks API to inject stubs
that trigger IRGen & Codegen of their respective function bodies when they are
first called.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229466 91177308-0d34-0410-b5e6-96231b3b80d8

examples/Kaleidoscope/Orc/fully_lazy/CMakeLists.txt

@@ -0,0 +1,12 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  ExecutionEngine
+  Object
+  RuntimeDyld
+  Support
+  native
+  )
+
+add_kaleidoscope_chapter(Kaleidoscope-Orc-lazy_irgen
+  toy.cpp
+  )

examples/Kaleidoscope/Orc/fully_lazy/Makefile

@@ -0,0 +1,9 @@
+.PHONY: all
+all: toy
+
+toy: toy.cpp
+	clang++ -Wall -std=c++11 toy.cpp -g -O0 -rdynamic -fno-rtti `llvm-config --cppflags --ldflags --system-libs --libs core orcjit native` -o toy
+
+.PHONY: clean
+clean:
+	rm -f toy

examples/Kaleidoscope/Orc/fully_lazy/README.txt

@@ -0,0 +1,21 @@
+//===----------------------------------------------------------------------===/
+//                 Kaleidoscope with Orc - Lazy IRGen Version
+//===----------------------------------------------------------------------===//
+
+This version of Kaleidoscope with Orc demonstrates fully lazy IR-generation.
+Building on the lazy-irgen version of the tutorial, this version injects JIT
+callbacks to defer the bulk of IR-generation and code-generation of functions until
+they are first called.
+
+When a function definition is entered, a JIT callback is created and a stub
+function is built that will call the body of the function indirectly. The body of
+the function is *not* IRGen'd at this point. Instead, the function pointer for
+the indirect call is initialized to point at the JIT callback, and the compile
+action for the callback is initialized with a lambda that IRGens the body of the
+function and adds it to the JIT. The function pointer is updated by the JIT
+callback's update action to point at the newly emitted function body, so future
+calls to the stub will go straight to the body, not through the JIT.
+
+This directory contains a Makefile that allows the code to be built in a
+standalone manner, independent of the larger LLVM build infrastructure. To build
+the program you will need to have 'clang++' and 'llvm-config' in your path.