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docs/tutorial/LangImpl5.rst

	==================================================	========================================
	Kaleidoscope: Extending the Language: Control Flow	Kaleidoscope: Compiling to Object Code
	==================================================	========================================

	.. contents::	.. contents::
	:local:	:local:
Context not available.
	Chapter 5 Introduction	Chapter 5 Introduction
	======================	======================

	Welcome to Chapter 5 of the "`Implementing a language with	Welcome to Chapter 5 of the "`Implementing a language with LLVM
	LLVM <index.html>`_" tutorial. Parts 1-4 described the implementation of	<index.html>`_" tutorial. This chapter describes how to compile our
	the simple Kaleidoscope language and included support for generating	language down to object files.
	LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as
	presented, Kaleidoscope is mostly useless: it has no control flow other
	than call and return. This means that you can't have conditional
	branches in the code, significantly limiting its power. In this episode
	of "build that compiler", we'll extend Kaleidoscope to have an
	if/then/else expression plus a simple 'for' loop.

	If/Then/Else
	============

	Extending Kaleidoscope to support if/then/else is quite straightforward.
	It basically requires adding support for this "new" concept to the
	lexer, parser, AST, and LLVM code emitter. This example is nice, because
	it shows how easy it is to "grow" a language over time, incrementally
	extending it as new ideas are discovered.

	Before we get going on "how" we add this extension, lets talk about
	"what" we want. The basic idea is that we want to be able to write this
	sort of thing:

	::	Choosing a target
		=================
	def fib(x)
	if x < 3 then
	1
	else
	fib(x-1)+fib(x-2);

	In Kaleidoscope, every construct is an expression: there are no	LLVM has native support for cross-compilation. You can compile to the
	statements. As such, the if/then/else expression needs to return a value	architecture of your current machine, or just as easily compile for
	like any other. Since we're using a mostly functional form, we'll have	other architectures. In this tutorial, we'll target the current
	it evaluate its conditional, then return the 'then' or 'else' value	machine.
	based on how the condition was resolved. This is very similar to the C
	"?:" expression.

	The semantics of the if/then/else expression is that it evaluates the	To specify the architecture that you want to target, we use a string
	condition to a boolean equality value: 0.0 is considered to be false and	called a "target triple". This takes the form
	everything else is considered to be true. If the condition is true, the	``<arch><sub>-<vendor>-<sys>-<abi>`` (see the `cross compilation docs
	first subexpression is evaluated and returned, if the condition is	<http://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_).
	false, the second subexpression is evaluated and returned. Since
	Kaleidoscope allows side-effects, this behavior is important to nail
	down.

	Now that we know what we "want", lets break this down into its	As an example, we can see what clang thinks is our current target
	constituent pieces.	triple:

	Lexer Extensions for If/Then/Else	::
	---------------------------------

	The lexer extensions are straightforward. First we add new enum values	$ clang --version \| grep Target
	for the relevant tokens:	Target: x86_64-unknown-linux-gnu

	.. code-block:: c++	Running this command may show something different on your machine as
		you might be using a different architecture or operating system to me.

	// control	Fortunately, we don't need to hard-code a target triple to target the
	tok_if = -6,	current machine. LLVM provides ``sys::getDefaultTargetTriple``, which
	tok_then = -7,	returns the target triple of the current machine.
	tok_else = -8,

	Once we have that, we recognize the new keywords in the lexer. This is
	pretty simple stuff:

	.. code-block:: c++	.. code-block:: c++

	...	auto TargetTriple = sys::getDefaultTargetTriple();
	if (IdentifierStr == "def")
	return tok_def;
	if (IdentifierStr == "extern")
	return tok_extern;
	if (IdentifierStr == "if")
	return tok_if;
	if (IdentifierStr == "then")
	return tok_then;
	if (IdentifierStr == "else")
	return tok_else;
	return tok_identifier;

	AST Extensions for If/Then/Else	LLVM doesn't require us to to link in all the target
	-------------------------------	functionality. For example, if we're just using the JIT, we don't need
		the assembly printers. Similarly, if we're only targetting certain
		architectures, we can only link in the functionality for those
		architectures.

	To represent the new expression we add a new AST node for it:	For this example, we'll initialize all the targets for emitting object
		code.

	.. code-block:: c++	.. code-block:: c++

	/// IfExprAST - Expression class for if/then/else.	InitializeAllTargetInfos();
	class IfExprAST : public ExprAST {	InitializeAllTargets();
	std::unique_ptr<ExprAST> Cond, Then, Else;	InitializeAllTargetMCs();
		InitializeAllAsmParsers();
	public:	InitializeAllAsmPrinters();
	IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
	std::unique_ptr<ExprAST> Else)
	: Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
	virtual Value *codegen();
	};

	The AST node just has pointers to the various subexpressions.

	Parser Extensions for If/Then/Else	We can now use our target triple to get a ``Target``:
	----------------------------------

	Now that we have the relevant tokens coming from the lexer and we have
	the AST node to build, our parsing logic is relatively straightforward.
	First we define a new parsing function:

	.. code-block:: c++	.. code-block:: c++

	/// ifexpr ::= 'if' expression 'then' expression 'else' expression	std::string Error;
	static std::unique_ptr<ExprAST> ParseIfExpr() {	auto Target = TargetRegistry::lookupTarget(TargetTriple, Error);
	getNextToken(); // eat the if.

	// condition.
	auto Cond = ParseExpression();
	if (!Cond)
	return nullptr;

	if (CurTok != tok_then)
	return Error("expected then");
	getNextToken(); // eat the then

	auto Then = ParseExpression();
	if (!Then)
	return nullptr;

	if (CurTok != tok_else)
	return Error("expected else");

	getNextToken();

	auto Else = ParseExpression();	// Print an error and exit if we couldn't find the requested target.
	if (!Else)	// This generally occurs if we've forgotten to initialise the
	return nullptr;	// TargetRegistry or we have a bogus target triple.
		if (!Target) {
		errs() << Error;
		return 1;
		}

	return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),	Target Machine
	std::move(Else));	==============
	}

	Next we hook it up as a primary expression:

	.. code-block:: c++

	static std::unique_ptr<ExprAST> ParsePrimary() {
	switch (CurTok) {
	default:
	return Error("unknown token when expecting an expression");
	case tok_identifier:
	return ParseIdentifierExpr();
	case tok_number:
	return ParseNumberExpr();
	case '(':
	return ParseParenExpr();
	case tok_if:
	return ParseIfExpr();
	}
	}

	LLVM IR for If/Then/Else
	------------------------

	Now that we have it parsing and building the AST, the final piece is	We will also need a ``TargetMachine``. This class provides a complete
	adding LLVM code generation support. This is the most interesting part	machine description of the machine we're targetting. If we want to
	of the if/then/else example, because this is where it starts to	target a specific feature (such as SSE) or a specific CPU (such as
	introduce new concepts. All of the code above has been thoroughly	Intel's Sandylake), we do so now.
	described in previous chapters.

	To motivate the code we want to produce, lets take a look at a simple	To see which features and CPUs that LLVM knows about, we can use
	example. Consider:	``llc``. For example, let's look at x86:

	::	::

	extern foo();	$ llvm-as < /dev/null \| llc -march=x86 -mattr=help
	extern bar();	Available CPUs for this target:
	def baz(x) if x then foo() else bar();

	If you disable optimizations, the code you'll (soon) get from	amdfam10 - Select the amdfam10 processor.
	Kaleidoscope looks like this:	athlon - Select the athlon processor.
		athlon-4 - Select the athlon-4 processor.
		...

	.. code-block:: llvm	Available features for this target:

	declare double @foo()	16bit-mode - 16-bit mode (i8086).
		32bit-mode - 32-bit mode (80386).
	declare double @bar()	3dnow - Enable 3DNow! instructions.
		3dnowa - Enable 3DNow! Athlon instructions.
	define double @baz(double %x) {	...
	entry:
	%ifcond = fcmp one double %x, 0.000000e+00
	br i1 %ifcond, label %then, label %else

	then: ; preds = %entry
	%calltmp = call double @foo()
	br label %ifcont

	else: ; preds = %entry
	%calltmp1 = call double @bar()
	br label %ifcont

	ifcont: ; preds = %else, %then
	%iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ]
	ret double %iftmp
	}

	To visualize the control flow graph, you can use a nifty feature of the	For our example, we'll use the generic CPU without any additional
	LLVM '`opt <http://llvm.org/cmds/opt.html>`_' tool. If you put this LLVM	features.
	IR into "t.ll" and run "``llvm-as < t.ll \| opt -analyze -view-cfg``", `a
	window will pop up <../ProgrammersManual.html#viewing-graphs-while-debugging-code>`_ and you'll
	see this graph:

	.. figure:: LangImpl5-cfg.png
	:align: center
	:alt: Example CFG

	Example CFG

	Another way to get this is to call "``F->viewCFG()``" or
	"``F->viewCFGOnly()``" (where F is a "``Function*``") either by
	inserting actual calls into the code and recompiling or by calling these
	in the debugger. LLVM has many nice features for visualizing various
	graphs.

	Getting back to the generated code, it is fairly simple: the entry block
	evaluates the conditional expression ("x" in our case here) and compares
	the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered
	and Not Equal"). Based on the result of this expression, the code jumps
	to either the "then" or "else" blocks, which contain the expressions for
	the true/false cases.

	Once the then/else blocks are finished executing, they both branch back
	to the 'ifcont' block to execute the code that happens after the
	if/then/else. In this case the only thing left to do is to return to the
	caller of the function. The question then becomes: how does the code
	know which expression to return?

	The answer to this question involves an important SSA operation: the
	`Phi
	operation <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_.
	If you're not familiar with SSA, `the wikipedia
	article <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_
	is a good introduction and there are various other introductions to it
	available on your favorite search engine. The short version is that
	"execution" of the Phi operation requires "remembering" which block
	control came from. The Phi operation takes on the value corresponding to
	the input control block. In this case, if control comes in from the
	"then" block, it gets the value of "calltmp". If control comes from the
	"else" block, it gets the value of "calltmp1".

	At this point, you are probably starting to think "Oh no! This means my
	simple and elegant front-end will have to start generating SSA form in
	order to use LLVM!". Fortunately, this is not the case, and we strongly
	advise not implementing an SSA construction algorithm in your
	front-end unless there is an amazingly good reason to do so. In
	practice, there are two sorts of values that float around in code
	written for your average imperative programming language that might need
	Phi nodes:

	#. Code that involves user variables: ``x = 1; x = x + 1;``
	#. Values that are implicit in the structure of your AST, such as the
	Phi node in this case.

	In `Chapter 7 <LangImpl7.html>`_ of this tutorial ("mutable variables"),
	we'll talk about #1 in depth. For now, just believe me that you don't
	need SSA construction to handle this case. For #2, you have the choice
	of using the techniques that we will describe for #1, or you can insert
	Phi nodes directly, if convenient. In this case, it is really
	easy to generate the Phi node, so we choose to do it directly.

	Okay, enough of the motivation and overview, lets generate code!

	Code Generation for If/Then/Else
	--------------------------------

	In order to generate code for this, we implement the ``codegen`` method
	for ``IfExprAST``:

	.. code-block:: c++	.. code-block:: c++

	Value *IfExprAST::codegen() {	auto CPU = "generic";
	Value *CondV = Cond->codegen();	auto Features = "";
	if (!CondV)
	return nullptr;

	// Convert condition to a bool by comparing equal to 0.0.	TargetOptions opt;
	CondV = Builder.CreateFCmpONE(	auto TargetMachine = Target->createTargetMachine(TargetTriple, CPU, Features, opt);
	CondV, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "ifcond");

	This code is straightforward and similar to what we saw before. We emit
	the expression for the condition, then compare that value to zero to get
	a truth value as a 1-bit (bool) value.

	.. code-block:: c++	Configuring the Module
		======================

	Function *TheFunction = Builder.GetInsertBlock()->getParent();	We're now ready to configure our module, to specify the target and
		data layout. This isn't strictly necessary, but the `frontend
	// Create blocks for the then and else cases. Insert the 'then' block at the	performance guide <../Frontend/PerformanceTips.html>`_ recommends
	// end of the function.	this. Optimizations benefit from knowing about the target and data
	BasicBlock *ThenBB =	layout.
	BasicBlock::Create(getGlobalContext(), "then", TheFunction);
	BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
	BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");

	Builder.CreateCondBr(CondV, ThenBB, ElseBB);

	This code creates the basic blocks that are related to the if/then/else
	statement, and correspond directly to the blocks in the example above.
	The first line gets the current Function object that is being built. It
	gets this by asking the builder for the current BasicBlock, and asking
	that block for its "parent" (the function it is currently embedded
	into).

	Once it has that, it creates three blocks. Note that it passes
	"TheFunction" into the constructor for the "then" block. This causes the
	constructor to automatically insert the new block into the end of the
	specified function. The other two blocks are created, but aren't yet
	inserted into the function.

	Once the blocks are created, we can emit the conditional branch that
	chooses between them. Note that creating new blocks does not implicitly
	affect the IRBuilder, so it is still inserting into the block that the
	condition went into. Also note that it is creating a branch to the
	"then" block and the "else" block, even though the "else" block isn't
	inserted into the function yet. This is all ok: it is the standard way
	that LLVM supports forward references.

	.. code-block:: c++	.. code-block:: c++

	// Emit then value.	TheModule->setDataLayout(TargetMachine->createDataLayout());
	Builder.SetInsertPoint(ThenBB);	TheModule->setTargetTriple(TargetTriple);

	Value *ThenV = Then->codegen();	Emit Object Code
	if (!ThenV)	================
	return nullptr;

	Builder.CreateBr(MergeBB);
	// Codegen of 'Then' can change the current block, update ThenBB for the PHI.
	ThenBB = Builder.GetInsertBlock();

	After the conditional branch is inserted, we move the builder to start
	inserting into the "then" block. Strictly speaking, this call moves the
	insertion point to be at the end of the specified block. However, since
	the "then" block is empty, it also starts out by inserting at the
	beginning of the block. :)

	Once the insertion point is set, we recursively codegen the "then"
	expression from the AST. To finish off the "then" block, we create an
	unconditional branch to the merge block. One interesting (and very
	important) aspect of the LLVM IR is that it `requires all basic blocks
	to be "terminated" <../LangRef.html#functionstructure>`_ with a `control
	flow instruction <../LangRef.html#terminators>`_ such as return or
	branch. This means that all control flow, including fall throughs must
	be made explicit in the LLVM IR. If you violate this rule, the verifier
	will emit an error.

	The final line here is quite subtle, but is very important. The basic
	issue is that when we create the Phi node in the merge block, we need to
	set up the block/value pairs that indicate how the Phi will work.
	Importantly, the Phi node expects to have an entry for each predecessor
	of the block in the CFG. Why then, are we getting the current block when
	we just set it to ThenBB 5 lines above? The problem is that the "Then"
	expression may actually itself change the block that the Builder is
	emitting into if, for example, it contains a nested "if/then/else"
	expression. Because calling ``codegen()`` recursively could arbitrarily change
	the notion of the current block, we are required to get an up-to-date
	value for code that will set up the Phi node.

	.. code-block:: c++	We're ready to emit object code! Let's define where we want to write
		our file to:

	// Emit else block.	.. code-block:: c++
	TheFunction->getBasicBlockList().push_back(ElseBB);
	Builder.SetInsertPoint(ElseBB);

	Value *ElseV = Else->codegen();	auto Filename = "output.o";
	if (!ElseV)	std::error_code EC;
	return nullptr;	raw_fd_ostream dest(Filename, EC, sys::fs::F_None);

	Builder.CreateBr(MergeBB);	if (EC) {
	// codegen of 'Else' can change the current block, update ElseBB for the PHI.	errs() << "Could not open file: " << EC.message();
	ElseBB = Builder.GetInsertBlock();	return 1;
		}

	Code generation for the 'else' block is basically identical to codegen	Finally, we define a pass that emits object code, then we run that
	for the 'then' block. The only significant difference is the first line,	pass:
	which adds the 'else' block to the function. Recall previously that the
	'else' block was created, but not added to the function. Now that the
	'then' and 'else' blocks are emitted, we can finish up with the merge
	code:

	.. code-block:: c++	.. code-block:: c++

	// Emit merge block.	legacy::PassManager pass;
	TheFunction->getBasicBlockList().push_back(MergeBB);	auto FileType = TargetMachine::CGFT_ObjectFile;
	Builder.SetInsertPoint(MergeBB);
	PHINode *PN =
	Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, "iftmp");

	PN->addIncoming(ThenV, ThenBB);	if (TargetMachine->addPassesToEmitFile(pass, dest, FileType)) {
	PN->addIncoming(ElseV, ElseBB);	errs() << "TargetMachine can't emit a file of this type";
	return PN;	return 1;
	}	}

	The first two lines here are now familiar: the first adds the "merge"	pass.run(*TheModule);
	block to the Function object (it was previously floating, like the else	dest.flush();
	block above). The second changes the insertion point so that newly
	created code will go into the "merge" block. Once that is done, we need
	to create the PHI node and set up the block/value pairs for the PHI.

	Finally, the CodeGen function returns the phi node as the value computed	Putting It All Together
	by the if/then/else expression. In our example above, this returned	=======================
	value will feed into the code for the top-level function, which will
	create the return instruction.

	Overall, we now have the ability to execute conditional code in	Does it work? Let's give it a try. We need to compile our code, but
	Kaleidoscope. With this extension, Kaleidoscope is a fairly complete	note that the arguments to ``llvm-config`` are different to the previous chapters.
	language that can calculate a wide variety of numeric functions. Next up
	we'll add another useful expression that is familiar from non-functional
	languages...

	'for' Loop Expression
	=====================

	Now that we know how to add basic control flow constructs to the
	language, we have the tools to add more powerful things. Lets add
	something more aggressive, a 'for' expression:

	::	::

	extern putchard(char)	$ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs all` -o toy
	def printstar(n)
	for i = 1, i < n, 1.0 in
	putchard(42); # ascii 42 = '*'

	# print 100 '*' characters
	printstar(100);

	This expression defines a new variable ("i" in this case) which iterates
	from a starting value, while the condition ("i < n" in this case) is
	true, incrementing by an optional step value ("1.0" in this case). If
	the step value is omitted, it defaults to 1.0. While the loop is true,
	it executes its body expression. Because we don't have anything better
	to return, we'll just define the loop as always returning 0.0. In the
	future when we have mutable variables, it will get more useful.

	As before, lets talk about the changes that we need to Kaleidoscope to
	support this.

	Lexer Extensions for the 'for' Loop
	-----------------------------------

	The lexer extensions are the same sort of thing as for if/then/else:

	.. code-block:: c++

	... in enum Token ...	Let's run it, and define a simple ``average`` function. Press Ctrl-D
	// control	when you're done.
	tok_if = -6, tok_then = -7, tok_else = -8,
	tok_for = -9, tok_in = -10

	... in gettok ...
	if (IdentifierStr == "def")
	return tok_def;
	if (IdentifierStr == "extern")
	return tok_extern;
	if (IdentifierStr == "if")
	return tok_if;
	if (IdentifierStr == "then")
	return tok_then;
	if (IdentifierStr == "else")
	return tok_else;
	if (IdentifierStr == "for")
	return tok_for;
	if (IdentifierStr == "in")
	return tok_in;
	return tok_identifier;

	AST Extensions for the 'for' Loop
	---------------------------------

	The AST node is just as simple. It basically boils down to capturing the
	variable name and the constituent expressions in the node.

	.. code-block:: c++	::

	/// ForExprAST - Expression class for for/in.	$ ./toy
	class ForExprAST : public ExprAST {	ready> def average(x y) (x + y) * 0.5;
	std::string VarName;	^D
	std::unique_ptr<ExprAST> Start, End, Step, Body;	Wrote output.o

	public:
	ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
	std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
	std::unique_ptr<ExprAST> Body)
	: VarName(VarName), Start(std::move(Start)), End(std::move(End)),
	Step(std::move(Step)), Body(std::move(Body)) {}
	virtual Value *codegen();
	};

	Parser Extensions for the 'for' Loop
	------------------------------------

	The parser code is also fairly standard. The only interesting thing here	We have an object file! To test it, let's write a simple program and
	is handling of the optional step value. The parser code handles it by	link it with our output. Here's the source code:
	checking to see if the second comma is present. If not, it sets the step
	value to null in the AST node:

	.. code-block:: c++	.. code-block:: c++

	/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression	#include <iostream>
	static std::unique_ptr<ExprAST> ParseForExpr() {
	getNextToken(); // eat the for.

	if (CurTok != tok_identifier)
	return Error("expected identifier after for");

	std::string IdName = IdentifierStr;
	getNextToken(); // eat identifier.

	if (CurTok != '=')
	return Error("expected '=' after for");
	getNextToken(); // eat '='.


	auto Start = ParseExpression();
	if (!Start)
	return nullptr;
	if (CurTok != ',')
	return Error("expected ',' after for start value");
	getNextToken();

	auto End = ParseExpression();
	if (!End)
	return nullptr;

	// The step value is optional.
	std::unique_ptr<ExprAST> Step;
	if (CurTok == ',') {
	getNextToken();
	Step = ParseExpression();
	if (!Step)
	return nullptr;
	}

	if (CurTok != tok_in)	extern "C" {
	return Error("expected 'in' after for");	double average(double, double);
	getNextToken(); // eat 'in'.

	auto Body = ParseExpression();
	if (!Body)
	return nullptr;

	return llvm::make_unique<ForExprAST>(IdName, std::move(Start),
	std::move(End), std::move(Step),
	std::move(Body));
	}	}

	LLVM IR for the 'for' Loop	int main() {
	--------------------------	std::cout << "average of 3.0 and 4.0: " << average(3.0, 4.0) << std::endl;

	Now we get to the good part: the LLVM IR we want to generate for this
	thing. With the simple example above, we get this LLVM IR (note that
	this dump is generated with optimizations disabled for clarity):

	.. code-block:: llvm

	declare double @putchard(double)

	define double @printstar(double %n) {
	entry:
	; initial value = 1.0 (inlined into phi)
	br label %loop

	loop: ; preds = %loop, %entry
	%i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ]
	; body
	%calltmp = call double @putchard(double 4.200000e+01)
	; increment
	%nextvar = fadd double %i, 1.000000e+00

	; termination test
	%cmptmp = fcmp ult double %i, %n
	%booltmp = uitofp i1 %cmptmp to double
	%loopcond = fcmp one double %booltmp, 0.000000e+00
	br i1 %loopcond, label %loop, label %afterloop

	afterloop: ; preds = %loop
	; loop always returns 0.0
	ret double 0.000000e+00
	}	}

	This loop contains all the same constructs we saw before: a phi node,	We link our program to output.o and check the result is what we
	several expressions, and some basic blocks. Lets see how this fits	expected:
	together.

	Code Generation for the 'for' Loop
	----------------------------------

	The first part of codegen is very simple: we just output the start
	expression for the loop value:

	.. code-block:: c++

	Value *ForExprAST::codegen() {
	// Emit the start code first, without 'variable' in scope.
	Value *StartVal = Start->codegen();
	if (StartVal == 0) return 0;

	With this out of the way, the next step is to set up the LLVM basic
	block for the start of the loop body. In the case above, the whole loop
	body is one block, but remember that the body code itself could consist
	of multiple blocks (e.g. if it contains an if/then/else or a for/in
	expression).

	.. code-block:: c++

	// Make the new basic block for the loop header, inserting after current
	// block.
	Function *TheFunction = Builder.GetInsertBlock()->getParent();
	BasicBlock *PreheaderBB = Builder.GetInsertBlock();
	BasicBlock *LoopBB =
	BasicBlock::Create(getGlobalContext(), "loop", TheFunction);

	// Insert an explicit fall through from the current block to the LoopBB.
	Builder.CreateBr(LoopBB);

	This code is similar to what we saw for if/then/else. Because we will
	need it to create the Phi node, we remember the block that falls through
	into the loop. Once we have that, we create the actual block that starts
	the loop and create an unconditional branch for the fall-through between
	the two blocks.

	.. code-block:: c++

	// Start insertion in LoopBB.
	Builder.SetInsertPoint(LoopBB);

	// Start the PHI node with an entry for Start.
	PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
	2, VarName.c_str());
	Variable->addIncoming(StartVal, PreheaderBB);

	Now that the "preheader" for the loop is set up, we switch to emitting
	code for the loop body. To begin with, we move the insertion point and
	create the PHI node for the loop induction variable. Since we already
	know the incoming value for the starting value, we add it to the Phi
	node. Note that the Phi will eventually get a second value for the
	backedge, but we can't set it up yet (because it doesn't exist!).

	.. code-block:: c++	::

	// Within the loop, the variable is defined equal to the PHI node. If it
	// shadows an existing variable, we have to restore it, so save it now.
	Value *OldVal = NamedValues[VarName];
	NamedValues[VarName] = Variable;

	// Emit the body of the loop. This, like any other expr, can change the
	// current BB. Note that we ignore the value computed by the body, but don't
	// allow an error.
	if (!Body->codegen())
	return nullptr;

	Now the code starts to get more interesting. Our 'for' loop introduces a
	new variable to the symbol table. This means that our symbol table can
	now contain either function arguments or loop variables. To handle this,
	before we codegen the body of the loop, we add the loop variable as the
	current value for its name. Note that it is possible that there is a
	variable of the same name in the outer scope. It would be easy to make
	this an error (emit an error and return null if there is already an
	entry for VarName) but we choose to allow shadowing of variables. In
	order to handle this correctly, we remember the Value that we are
	potentially shadowing in ``OldVal`` (which will be null if there is no
	shadowed variable).

	Once the loop variable is set into the symbol table, the code
	recursively codegen's the body. This allows the body to use the loop
	variable: any references to it will naturally find it in the symbol
	table.

	.. code-block:: c++

	// Emit the step value.
	Value *StepVal = nullptr;
	if (Step) {
	StepVal = Step->codegen();
	if (!StepVal)
	return nullptr;
	} else {
	// If not specified, use 1.0.
	StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
	}

	Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");

	Now that the body is emitted, we compute the next value of the iteration
	variable by adding the step value, or 1.0 if it isn't present.
	'``NextVar``' will be the value of the loop variable on the next
	iteration of the loop.

	.. code-block:: c++

	// Compute the end condition.
	Value *EndCond = End->codegen();
	if (!EndCond)
	return nullptr;

	// Convert condition to a bool by comparing equal to 0.0.
	EndCond = Builder.CreateFCmpONE(
	EndCond, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "loopcond");

	Finally, we evaluate the exit value of the loop, to determine whether
	the loop should exit. This mirrors the condition evaluation for the
	if/then/else statement.

	.. code-block:: c++

	// Create the "after loop" block and insert it.
	BasicBlock *LoopEndBB = Builder.GetInsertBlock();
	BasicBlock *AfterBB =
	BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);

	// Insert the conditional branch into the end of LoopEndBB.
	Builder.CreateCondBr(EndCond, LoopBB, AfterBB);

	// Any new code will be inserted in AfterBB.
	Builder.SetInsertPoint(AfterBB);

	With the code for the body of the loop complete, we just need to finish
	up the control flow for it. This code remembers the end block (for the
	phi node), then creates the block for the loop exit ("afterloop"). Based
	on the value of the exit condition, it creates a conditional branch that
	chooses between executing the loop again and exiting the loop. Any
	future code is emitted in the "afterloop" block, so it sets the
	insertion position to it.

	.. code-block:: c++

	// Add a new entry to the PHI node for the backedge.
	Variable->addIncoming(NextVar, LoopEndBB);

	// Restore the unshadowed variable.
	if (OldVal)
	NamedValues[VarName] = OldVal;
	else
	NamedValues.erase(VarName);

	// for expr always returns 0.0.
	return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
	}

	The final code handles various cleanups: now that we have the "NextVar"	$ clang++ main.cpp output.o -o main
	value, we can add the incoming value to the loop PHI node. After that,	$ ./main
	we remove the loop variable from the symbol table, so that it isn't in	average of 3.0 and 4.0: 3.5
	scope after the for loop. Finally, code generation of the for loop
	always returns 0.0, so that is what we return from
	``ForExprAST::codegen()``.

	With this, we conclude the "adding control flow to Kaleidoscope" chapter
	of the tutorial. In this chapter we added two control flow constructs,
	and used them to motivate a couple of aspects of the LLVM IR that are
	important for front-end implementors to know. In the next chapter of our
	saga, we will get a bit crazier and add `user-defined
	operators <LangImpl6.html>`_ to our poor innocent language.

	Full Code Listing	Full Code Listing
	=================	=================

	Here is the complete code listing for our running example, enhanced with
	the if/then/else and for expressions.. To build this example, use:

	.. code-block:: bash

	# Compile
	clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
	# Run
	./toy

	Here is the code:

	.. literalinclude:: ../../examples/Kaleidoscope/Chapter5/toy.cpp	.. literalinclude:: ../../examples/Kaleidoscope/Chapter5/toy.cpp
	:language: c++	:language: c++

	`Next: Extending the language: user-defined operators <LangImpl6.html>`_

Context not available.

examples/Kaleidoscope/Chapter5/toy.cpp

	#include "llvm/ADT/STLExtras.h"	#include "llvm/IR/Verifier.h"
	#include "llvm/Analysis/Passes.h"	#include "llvm/IR/DerivedTypes.h"
	#include "llvm/IR/IRBuilder.h"	#include "llvm/IR/IRBuilder.h"
	#include "llvm/IR/LLVMContext.h"	#include "llvm/IR/LLVMContext.h"
	#include "llvm/IR/LegacyPassManager.h"
	#include "llvm/IR/Module.h"	#include "llvm/IR/Module.h"
	#include "llvm/IR/Verifier.h"	#include "llvm/Support/FileSystem.h"
		#include "llvm/IR/LegacyPassManager.h"
		#include "llvm/Support/TargetRegistry.h"
	#include "llvm/Support/TargetSelect.h"	#include "llvm/Support/TargetSelect.h"
	#include "llvm/Transforms/Scalar.h"	#include "llvm/Support/raw_ostream.h"
		#include "llvm/Target/TargetMachine.h"
	#include <cctype>	#include <cctype>
	#include <cstdio>	#include <cstdio>
	#include <map>	#include <map>
	#include <string>	#include <string>
	#include <vector>	#include <vector>
	#include "../include/KaleidoscopeJIT.h"

	using namespace llvm;	using namespace llvm;
	using namespace llvm::orc;

	//===----------------------------------------------------------------------===//	//===----------------------------------------------------------------------===//
	// Lexer	// Lexer
Context not available.

	// primary	// primary
	tok_identifier = -4,	tok_identifier = -4,
	tok_number = -5,	tok_number = -5

	// control
	tok_if = -6,
	tok_then = -7,
	tok_else = -8,
	tok_for = -9,
	tok_in = -10
	};	};

	static std::string IdentifierStr; // Filled in if tok_identifier	static std::string IdentifierStr; // Filled in if tok_identifier
Context not available.
	return tok_def;	return tok_def;
	if (IdentifierStr == "extern")	if (IdentifierStr == "extern")
	return tok_extern;	return tok_extern;
	if (IdentifierStr == "if")
	return tok_if;
	if (IdentifierStr == "then")
	return tok_then;
	if (IdentifierStr == "else")
	return tok_else;
	if (IdentifierStr == "for")
	return tok_for;
	if (IdentifierStr == "in")
	return tok_in;
	return tok_identifier;	return tok_identifier;
	}	}

Context not available.
	Value *codegen() override;	Value *codegen() override;
	};	};

	/// IfExprAST - Expression class for if/then/else.
	class IfExprAST : public ExprAST {
	std::unique_ptr<ExprAST> Cond, Then, Else;

	public:
	IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
	std::unique_ptr<ExprAST> Else)
	: Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
	Value *codegen() override;
	};

	/// ForExprAST - Expression class for for/in.
	class ForExprAST : public ExprAST {
	std::string VarName;
	std::unique_ptr<ExprAST> Start, End, Step, Body;

	public:
	ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
	std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
	std::unique_ptr<ExprAST> Body)
	: VarName(VarName), Start(std::move(Start)), End(std::move(End)),
	Step(std::move(Step)), Body(std::move(Body)) {}
	Value *codegen() override;
	};

	/// PrototypeAST - This class represents the "prototype" for a function,	/// PrototypeAST - This class represents the "prototype" for a function,
	/// which captures its name, and its argument names (thus implicitly the number	/// which captures its name, and its argument names (thus implicitly the number
	/// of arguments the function takes).	/// of arguments the function takes).
Context not available.
	return llvm::make_unique<CallExprAST>(IdName, std::move(Args));	return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
	}	}

	/// ifexpr ::= 'if' expression 'then' expression 'else' expression
	static std::unique_ptr<ExprAST> ParseIfExpr() {
	getNextToken(); // eat the if.

	// condition.
	auto Cond = ParseExpression();
	if (!Cond)
	return nullptr;

	if (CurTok != tok_then)
	return Error("expected then");
	getNextToken(); // eat the then

	auto Then = ParseExpression();
	if (!Then)
	return nullptr;

	if (CurTok != tok_else)
	return Error("expected else");

	getNextToken();

	auto Else = ParseExpression();
	if (!Else)
	return nullptr;

	return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
	std::move(Else));
	}

	/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
	static std::unique_ptr<ExprAST> ParseForExpr() {
	getNextToken(); // eat the for.

	if (CurTok != tok_identifier)
	return Error("expected identifier after for");

	std::string IdName = IdentifierStr;
	getNextToken(); // eat identifier.

	if (CurTok != '=')
	return Error("expected '=' after for");
	getNextToken(); // eat '='.

	auto Start = ParseExpression();
	if (!Start)
	return nullptr;
	if (CurTok != ',')
	return Error("expected ',' after for start value");
	getNextToken();

	auto End = ParseExpression();
	if (!End)
	return nullptr;

	// The step value is optional.
	std::unique_ptr<ExprAST> Step;
	if (CurTok == ',') {
	getNextToken();
	Step = ParseExpression();
	if (!Step)
	return nullptr;
	}

	if (CurTok != tok_in)
	return Error("expected 'in' after for");
	getNextToken(); // eat 'in'.

	auto Body = ParseExpression();
	if (!Body)
	return nullptr;

	return llvm::make_unique<ForExprAST>(IdName, std::move(Start), std::move(End),
	std::move(Step), std::move(Body));
	}

	/// primary	/// primary
	/// ::= identifierexpr	/// ::= identifierexpr
	/// ::= numberexpr	/// ::= numberexpr
	/// ::= parenexpr	/// ::= parenexpr
	/// ::= ifexpr
	/// ::= forexpr
	static std::unique_ptr<ExprAST> ParsePrimary() {	static std::unique_ptr<ExprAST> ParsePrimary() {
	switch (CurTok) {	switch (CurTok) {
	default:	default:
Context not available.
	return ParseNumberExpr();	return ParseNumberExpr();
	case '(':	case '(':
	return ParseParenExpr();	return ParseParenExpr();
	case tok_if:
	return ParseIfExpr();
	case tok_for:
	return ParseForExpr();
	}	}
	}	}

Context not available.
	return nullptr;	return nullptr;
	}	}

	/// toplevelexpr ::= expression
	static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
	if (auto E = ParseExpression()) {
	// Make an anonymous proto.
	auto Proto = llvm::make_unique<PrototypeAST>("__anon_expr",
	std::vector<std::string>());
	return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
	}
	return nullptr;
	}

	/// external ::= 'extern' prototype	/// external ::= 'extern' prototype
	static std::unique_ptr<PrototypeAST> ParseExtern() {	static std::unique_ptr<PrototypeAST> ParseExtern() {
	getNextToken(); // eat extern.	getNextToken(); // eat extern.
Context not available.
	static IRBuilder<> Builder(getGlobalContext());	static IRBuilder<> Builder(getGlobalContext());
	static std::map<std::string, Value *> NamedValues;	static std::map<std::string, Value *> NamedValues;
	static std::unique_ptr<legacy::FunctionPassManager> TheFPM;	static std::unique_ptr<legacy::FunctionPassManager> TheFPM;
	static std::unique_ptr<KaleidoscopeJIT> TheJIT;
	static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;	static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;

	Value ErrorV(const char Str) {	Value ErrorV(const char Str) {
Context not available.
	return Builder.CreateCall(CalleeF, ArgsV, "calltmp");	return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
	}	}

	Value *IfExprAST::codegen() {
	Value *CondV = Cond->codegen();
	if (!CondV)
	return nullptr;

	// Convert condition to a bool by comparing equal to 0.0.
	CondV = Builder.CreateFCmpONE(
	CondV, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "ifcond");

	Function *TheFunction = Builder.GetInsertBlock()->getParent();

	// Create blocks for the then and else cases. Insert the 'then' block at the
	// end of the function.
	BasicBlock *ThenBB =
	BasicBlock::Create(getGlobalContext(), "then", TheFunction);
	BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else");
	BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont");

	Builder.CreateCondBr(CondV, ThenBB, ElseBB);

	// Emit then value.
	Builder.SetInsertPoint(ThenBB);

	Value *ThenV = Then->codegen();
	if (!ThenV)
	return nullptr;

	Builder.CreateBr(MergeBB);
	// Codegen of 'Then' can change the current block, update ThenBB for the PHI.
	ThenBB = Builder.GetInsertBlock();

	// Emit else block.
	TheFunction->getBasicBlockList().push_back(ElseBB);
	Builder.SetInsertPoint(ElseBB);

	Value *ElseV = Else->codegen();
	if (!ElseV)
	return nullptr;

	Builder.CreateBr(MergeBB);
	// Codegen of 'Else' can change the current block, update ElseBB for the PHI.
	ElseBB = Builder.GetInsertBlock();

	// Emit merge block.
	TheFunction->getBasicBlockList().push_back(MergeBB);
	Builder.SetInsertPoint(MergeBB);
	PHINode *PN =
	Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, "iftmp");

	PN->addIncoming(ThenV, ThenBB);
	PN->addIncoming(ElseV, ElseBB);
	return PN;
	}

	// Output for-loop as:
	// ...
	// start = startexpr
	// goto loop
	// loop:
	// variable = phi [start, loopheader], [nextvariable, loopend]
	// ...
	// bodyexpr
	// ...
	// loopend:
	// step = stepexpr
	// nextvariable = variable + step
	// endcond = endexpr
	// br endcond, loop, endloop
	// outloop:
	Value *ForExprAST::codegen() {
	// Emit the start code first, without 'variable' in scope.
	Value *StartVal = Start->codegen();
	if (!StartVal)
	return nullptr;

	// Make the new basic block for the loop header, inserting after current
	// block.
	Function *TheFunction = Builder.GetInsertBlock()->getParent();
	BasicBlock *PreheaderBB = Builder.GetInsertBlock();
	BasicBlock *LoopBB =
	BasicBlock::Create(getGlobalContext(), "loop", TheFunction);

	// Insert an explicit fall through from the current block to the LoopBB.
	Builder.CreateBr(LoopBB);

	// Start insertion in LoopBB.
	Builder.SetInsertPoint(LoopBB);

	// Start the PHI node with an entry for Start.
	PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()),
	2, VarName.c_str());
	Variable->addIncoming(StartVal, PreheaderBB);

	// Within the loop, the variable is defined equal to the PHI node. If it
	// shadows an existing variable, we have to restore it, so save it now.
	Value *OldVal = NamedValues[VarName];
	NamedValues[VarName] = Variable;

	// Emit the body of the loop. This, like any other expr, can change the
	// current BB. Note that we ignore the value computed by the body, but don't
	// allow an error.
	if (!Body->codegen())
	return nullptr;

	// Emit the step value.
	Value *StepVal = nullptr;
	if (Step) {
	StepVal = Step->codegen();
	if (!StepVal)
	return nullptr;
	} else {
	// If not specified, use 1.0.
	StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0));
	}

	Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar");

	// Compute the end condition.
	Value *EndCond = End->codegen();
	if (!EndCond)
	return nullptr;

	// Convert condition to a bool by comparing equal to 0.0.
	EndCond = Builder.CreateFCmpONE(
	EndCond, ConstantFP::get(getGlobalContext(), APFloat(0.0)), "loopcond");

	// Create the "after loop" block and insert it.
	BasicBlock *LoopEndBB = Builder.GetInsertBlock();
	BasicBlock *AfterBB =
	BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction);

	// Insert the conditional branch into the end of LoopEndBB.
	Builder.CreateCondBr(EndCond, LoopBB, AfterBB);

	// Any new code will be inserted in AfterBB.
	Builder.SetInsertPoint(AfterBB);

	// Add a new entry to the PHI node for the backedge.
	Variable->addIncoming(NextVar, LoopEndBB);

	// Restore the unshadowed variable.
	if (OldVal)
	NamedValues[VarName] = OldVal;
	else
	NamedValues.erase(VarName);

	// for expr always returns 0.0.
	return Constant::getNullValue(Type::getDoubleTy(getGlobalContext()));
	}

	Function *PrototypeAST::codegen() {	Function *PrototypeAST::codegen() {
	// Make the function type: double(double,double) etc.	// Make the function type: double(double,double) etc.
	std::vector<Type *> Doubles(Args.size(),	std::vector<Type *> Doubles(Args.size(),
Context not available.
	// Validate the generated code, checking for consistency.	// Validate the generated code, checking for consistency.
	verifyFunction(*TheFunction);	verifyFunction(*TheFunction);

	// Run the optimizer on the function.
	TheFPM->run(*TheFunction);

	return TheFunction;	return TheFunction;
	}	}

Context not available.
	}	}

	//===----------------------------------------------------------------------===//	//===----------------------------------------------------------------------===//
	// Top-Level parsing and JIT Driver	// Top-Level parsing
	//===----------------------------------------------------------------------===//	//===----------------------------------------------------------------------===//

	static void InitializeModuleAndPassManager() {
	// Open a new module.
	TheModule = llvm::make_unique<Module>("my cool jit", getGlobalContext());
	TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());

	// Create a new pass manager attached to it.
	TheFPM = llvm::make_unique<legacy::FunctionPassManager>(TheModule.get());

	// Do simple "peephole" optimizations and bit-twiddling optzns.
	TheFPM->add(createInstructionCombiningPass());
	// Reassociate expressions.
	TheFPM->add(createReassociatePass());
	// Eliminate Common SubExpressions.
	TheFPM->add(createGVNPass());
	// Simplify the control flow graph (deleting unreachable blocks, etc).
	TheFPM->add(createCFGSimplificationPass());

	TheFPM->doInitialization();
	}

	static void HandleDefinition() {	static void HandleDefinition() {
	if (auto FnAST = ParseDefinition()) {	if (auto FnAST = ParseDefinition()) {
	if (auto *FnIR = FnAST->codegen()) {	if (auto *FnIR = FnAST->codegen()) {
	fprintf(stderr, "Read function definition:");	fprintf(stderr, "Read function definition:");
	FnIR->dump();	FnIR->dump();
	TheJIT->addModule(std::move(TheModule));
	InitializeModuleAndPassManager();
	}	}
	} else {	} else {
	// Skip token for error recovery.	// Skip token for error recovery.
Context not available.
	}	}
	}	}

	static void HandleTopLevelExpression() {
	// Evaluate a top-level expression into an anonymous function.
	if (auto FnAST = ParseTopLevelExpr()) {
	if (FnAST->codegen()) {

	// JIT the module containing the anonymous expression, keeping a handle so
	// we can free it later.
	auto H = TheJIT->addModule(std::move(TheModule));
	InitializeModuleAndPassManager();

	// Search the JIT for the __anon_expr symbol.
	auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
	assert(ExprSymbol && "Function not found");

	// Get the symbol's address and cast it to the right type (takes no
	// arguments, returns a double) so we can call it as a native function.
	double (FP)() = (double ()())(intptr_t)ExprSymbol.getAddress();
	fprintf(stderr, "Evaluated to %f\n", FP());

	// Delete the anonymous expression module from the JIT.
	TheJIT->removeModule(H);
	}
	} else {
	// Skip token for error recovery.
	getNextToken();
	}
	}

	/// top ::= definition \| external \| expression \| ';'	/// top ::= definition \| external \| expression \| ';'
	static void MainLoop() {	static void MainLoop() {
	while (1) {	while (1) {
Context not available.
	case tok_extern:	case tok_extern:
	HandleExtern();	HandleExtern();
	break;	break;
	default:
	HandleTopLevelExpression();
	break;
	}	}
	}	}
	}	}
Context not available.
	//===----------------------------------------------------------------------===//	//===----------------------------------------------------------------------===//

	int main() {	int main() {
	InitializeNativeTarget();
	InitializeNativeTargetAsmPrinter();
	InitializeNativeTargetAsmParser();

	// Install standard binary operators.	// Install standard binary operators.
	// 1 is lowest precedence.	// 1 is lowest precedence.
	BinopPrecedence['<'] = 10;	BinopPrecedence['<'] = 10;
Context not available.
	fprintf(stderr, "ready> ");	fprintf(stderr, "ready> ");
	getNextToken();	getNextToken();

	TheJIT = llvm::make_unique<KaleidoscopeJIT>();	// Make the module, which holds all the code.
		TheModule = llvm::make_unique<Module>("my cool module", getGlobalContext());

	InitializeModuleAndPassManager();	auto TargetTriple = sys::getDefaultTargetTriple();
		TheModule->setTargetTriple(TargetTriple);

	// Run the main "interpreter loop" now.	// Run the main "interpreter loop" now.
	MainLoop();	MainLoop();

		// Initialize the target registry etc.
		InitializeAllTargetInfos();
		InitializeAllTargets();
		InitializeAllTargetMCs();
		InitializeAllAsmParsers();
		InitializeAllAsmPrinters();

		std::string Error;
		auto Target = TargetRegistry::lookupTarget(TargetTriple, Error);

		// Print an error and exit if we couldn't find the requested target.
		// This generally occurs if we've forgotten to initialise the
		// TargetRegistry or we have a bogus target triple.
		if (!Target) {
		errs() << Error;
		return 1;
		}

		auto CPU = "generic";
		auto Features = "";

		TargetOptions opt;
		auto TargetMachine =
		Target->createTargetMachine(TargetTriple, CPU, Features, opt);

		TheModule->setDataLayout(TargetMachine->createDataLayout());

		auto Filename = "output.o";
		std::error_code EC;
		raw_fd_ostream dest(Filename, EC, sys::fs::F_None);

		if (EC) {
		errs() << "Could not open file: " << EC.message();
		return 1;
		}

		legacy::PassManager pass;
		auto FileType = TargetMachine::CGFT_ObjectFile;

		if (TargetMachine->addPassesToEmitFile(pass, dest, FileType)) {
		errs() << "TargetMachine can't emit a file of this type";
		return 1;
		}

		pass.run(*TheModule);
		dest.flush();

		outs() << "Wrote " << Filename << "\n";

	return 0;	return 0;
	}	}
Context not available.

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