+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="dss_sparsebitvector">SparseBitVector</a>
+</div>
+
+<div class="doc_text">
+<p> The SparseBitVector container is much like BitVector, with one major
+difference: Only the bits that are set, are stored. This makes the
+SparseBitVector much more space efficient than BitVector when the set is sparse,
+as well as making set operations O(number of set bits) instead of O(size of
+universe). The downside to the SparseBitVector is that setting and testing of random bits is O(N), and on large SparseBitVectors, this can be slower than BitVector. In our implementation, setting or testing bits in sorted order
+(either forwards or reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends on size) of the current bit is also O(1). As a general statement, testing/setting bits in a SparseBitVector is O(distance away from last set bit).
+</p>
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="common">Helpful Hints for Common Operations</a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>This section describes how to perform some very simple transformations of
+LLVM code. This is meant to give examples of common idioms used, showing the
+practical side of LLVM transformations. <p> Because this is a "how-to" section,
+you should also read about the main classes that you will be working with. The
+<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
+and descriptions of the main classes that you should know about.</p>
+
+</div>
+
+<!-- NOTE: this section should be heavy on example code -->
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="inspection">Basic Inspection and Traversal Routines</a>
+</div>
+
+<div class="doc_text">
+
+<p>The LLVM compiler infrastructure have many different data structures that may
+be traversed. Following the example of the C++ standard template library, the
+techniques used to traverse these various data structures are all basically the
+same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
+method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
+function returns an iterator pointing to one past the last valid element of the
+sequence, and there is some <tt>XXXiterator</tt> data type that is common
+between the two operations.</p>
+
+<p>Because the pattern for iteration is common across many different aspects of
+the program representation, the standard template library algorithms may be used
+on them, and it is easier to remember how to iterate. First we show a few common
+examples of the data structures that need to be traversed. Other data
+structures are traversed in very similar ways.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="iterate_function">Iterating over the </a><a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
+transform in some way; in particular, you'd like to manipulate its
+<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
+the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
+an example that prints the name of a <tt>BasicBlock</tt> and the number of
+<tt>Instruction</tt>s it contains:</p>
+
+<div class="doc_code">
+<pre>
+// <i>func is a pointer to a Function instance</i>
+for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
+ // <i>Print out the name of the basic block if it has one, and then the</i>
+ // <i>number of instructions that it contains</i>
+ llvm::cerr << "Basic block (name=" << i->getName() << ") has "
+ << i->size() << " instructions.\n";
+</pre>
+</div>
+
+<p>Note that i can be used as if it were a pointer for the purposes of
+invoking member functions of the <tt>Instruction</tt> class. This is
+because the indirection operator is overloaded for the iterator
+classes. In the above code, the expression <tt>i->size()</tt> is
+exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="iterate_basicblock">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#BasicBlock"><tt>BasicBlock</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
+easy to iterate over the individual instructions that make up
+<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
+a <tt>BasicBlock</tt>:</p>
+
+<div class="doc_code">
+<pre>
+// <i>blk is a pointer to a BasicBlock instance</i>
+for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
+ // <i>The next statement works since operator<<(ostream&,...)</i>
+ // <i>is overloaded for Instruction&</i>
+ llvm::cerr << *i << "\n";
+</pre>
+</div>
+
+<p>However, this isn't really the best way to print out the contents of a
+<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
+anything you'll care about, you could have just invoked the print routine on the
+basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="iterate_institer">Iterating over the </a><a
+ href="#Instruction"><tt>Instruction</tt></a>s in a <a
+ href="#Function"><tt>Function</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
+<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
+<tt>InstIterator</tt> should be used instead. You'll need to include <a
+href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
+and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
+small example that shows how to dump all instructions in a function to the standard error stream:<p>
+
+<div class="doc_code">
+<pre>
+#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
+
+// <i>F is a pointer to a Function instance</i>
+for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ llvm::cerr << *I << "\n";
+</pre>
+</div>
+
+<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
+work list with its initial contents. For example, if you wanted to
+initialize a work list to contain all instructions in a <tt>Function</tt>
+F, all you would need to do is something like:</p>
+
+<div class="doc_code">
+<pre>
+std::set<Instruction*> worklist;
+// or better yet, SmallPtrSet<Instruction*, 64> worklist;
+
+for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
+ worklist.insert(&*I);
+</pre>
+</div>
+
+<p>The STL set <tt>worklist</tt> would now contain all instructions in the
+<tt>Function</tt> pointed to by F.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="iterate_convert">Turning an iterator into a class pointer (and
+ vice-versa)</a>
+</div>
+
+<div class="doc_text">
+
+<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
+instance when all you've got at hand is an iterator. Well, extracting
+a reference or a pointer from an iterator is very straight-forward.
+Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
+is a <tt>BasicBlock::const_iterator</tt>:</p>
+
+<div class="doc_code">
+<pre>
+Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
+Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
+const Instruction& inst = *j;
+</pre>
+</div>
+
+<p>However, the iterators you'll be working with in the LLVM framework are
+special: they will automatically convert to a ptr-to-instance type whenever they
+need to. Instead of dereferencing the iterator and then taking the address of
+the result, you can simply assign the iterator to the proper pointer type and
+you get the dereference and address-of operation as a result of the assignment
+(behind the scenes, this is a result of overloading casting mechanisms). Thus
+the last line of the last example,</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pinst = &*i;
+</pre>
+</div>
+
+<p>is semantically equivalent to</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pinst = i;
+</pre>
+</div>
+
+<p>It's also possible to turn a class pointer into the corresponding iterator,
+and this is a constant time operation (very efficient). The following code
+snippet illustrates use of the conversion constructors provided by LLVM
+iterators. By using these, you can explicitly grab the iterator of something
+without actually obtaining it via iteration over some structure:</p>
+
+<div class="doc_code">
+<pre>
+void printNextInstruction(Instruction* inst) {
+ BasicBlock::iterator it(inst);
+ ++it; // <i>After this line, it refers to the instruction after *inst</i>
+ if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
+}
+</pre>
+</div>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="iterate_complex">Finding call sites: a slightly more complex
+ example</a>
+</div>
+
+<div class="doc_text">
+
+<p>Say that you're writing a FunctionPass and would like to count all the
+locations in the entire module (that is, across every <tt>Function</tt>) where a
+certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
+learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
+much more straight-forward manner, but this example will allow us to explore how
+you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
+is what we want to do:</p>
+
+<div class="doc_code">
+<pre>
+initialize callCounter to zero
+for each Function f in the Module
+ for each BasicBlock b in f
+ for each Instruction i in b
+ if (i is a CallInst and calls the given function)
+ increment callCounter
+</pre>
+</div>
+
+<p>And the actual code is (remember, because we're writing a
+<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
+override the <tt>runOnFunction</tt> method):</p>
+
+<div class="doc_code">
+<pre>
+Function* targetFunc = ...;
+
+class OurFunctionPass : public FunctionPass {
+ public:
+ OurFunctionPass(): callCounter(0) { }
+
+ virtual runOnFunction(Function& F) {
+ for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
+ for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {
+ if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
+ href="#CallInst">CallInst</a>>(&*i)) {
+ // <i>We know we've encountered a call instruction, so we</i>
+ // <i>need to determine if it's a call to the</i>
+ // <i>function pointed to by m_func or not.</i>
+ if (callInst->getCalledFunction() == targetFunc)
+ ++callCounter;
+ }
+ }
+ }
+ }
+
+ private:
+ unsigned callCounter;
+};
+</pre>
+</div>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="calls_and_invokes">Treating calls and invokes the same way</a>
+</div>
+
+<div class="doc_text">
+
+<p>You may have noticed that the previous example was a bit oversimplified in
+that it did not deal with call sites generated by 'invoke' instructions. In
+this, and in other situations, you may find that you want to treat
+<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
+most-specific common base class is <tt>Instruction</tt>, which includes lots of
+less closely-related things. For these cases, LLVM provides a handy wrapper
+class called <a
+href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
+It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
+methods that provide functionality common to <tt>CallInst</tt>s and
+<tt>InvokeInst</tt>s.</p>
+
+<p>This class has "value semantics": it should be passed by value, not by
+reference and it should not be dynamically allocated or deallocated using
+<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
+assignable and constructable, with costs equivalents to that of a bare pointer.
+If you look at its definition, it has only a single pointer member.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="iterate_chains">Iterating over def-use & use-def chains</a>
+</div>
+
+<div class="doc_text">
+
+<p>Frequently, we might have an instance of the <a
+href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
+determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
+<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
+For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
+particular function <tt>foo</tt>. Finding all of the instructions that
+<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
+of <tt>F</tt>:</p>
+
+<div class="doc_code">
+<pre>
+Function *F = ...;
+
+for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
+ if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
+ llvm::cerr << "F is used in instruction:\n";
+ llvm::cerr << *Inst << "\n";
+ }
+</pre>
+</div>
+
+<p>Alternately, it's common to have an instance of the <a
+href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
+<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
+<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
+<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
+all of the values that a particular instruction uses (that is, the operands of
+the particular <tt>Instruction</tt>):</p>
+
+<div class="doc_code">
+<pre>
+Instruction *pi = ...;
+
+for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
+ Value *v = *i;
+ // <i>...</i>
+}
+</pre>
+</div>
+
+<!--
+ def-use chains ("finding all users of"): Value::use_begin/use_end
+ use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
+-->
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="iterate_preds">Iterating over predecessors &
+successors of blocks</a>
+</div>
+
+<div class="doc_text">
+
+<p>Iterating over the predecessors and successors of a block is quite easy
+with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
+this to iterate over all predecessors of BB:</p>
+
+<div class="doc_code">
+<pre>
+#include "llvm/Support/CFG.h"
+BasicBlock *BB = ...;
+
+for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *Pred = *PI;
+ // <i>...</i>
+}
+</pre>
+</div>
+
+<p>Similarly, to iterate over successors use
+succ_iterator/succ_begin/succ_end.</p>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="simplechanges">Making simple changes</a>
+</div>
+
+<div class="doc_text">
+
+<p>There are some primitive transformation operations present in the LLVM
+infrastructure that are worth knowing about. When performing
+transformations, it's fairly common to manipulate the contents of basic
+blocks. This section describes some of the common methods for doing so
+and gives example code.</p>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="schanges_creating">Creating and inserting new
+ <tt>Instruction</tt>s</a>
+</div>
+
+<div class="doc_text">
+
+<p><i>Instantiating Instructions</i></p>
+
+<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
+constructor for the kind of instruction to instantiate and provide the necessary
+parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
+(const-ptr-to) <tt>Type</tt>. Thus:</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* ai = new AllocaInst(Type::Int32Ty);
+</pre>
+</div>
+
+<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
+one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
+subclass is likely to have varying default parameters which change the semantics
+of the instruction, so refer to the <a
+href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
+Instruction</a> that you're interested in instantiating.</p>
+
+<p><i>Naming values</i></p>
+
+<p>It is very useful to name the values of instructions when you're able to, as
+this facilitates the debugging of your transformations. If you end up looking
+at generated LLVM machine code, you definitely want to have logical names
+associated with the results of instructions! By supplying a value for the
+<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
+associate a logical name with the result of the instruction's execution at
+run time. For example, say that I'm writing a transformation that dynamically
+allocates space for an integer on the stack, and that integer is going to be
+used as some kind of index by some other code. To accomplish this, I place an
+<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
+<tt>Function</tt>, and I'm intending to use it within the same
+<tt>Function</tt>. I might do:</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
+</pre>
+</div>
+
+<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
+execution value, which is a pointer to an integer on the run time stack.</p>
+
+<p><i>Inserting instructions</i></p>
+
+<p>There are essentially two ways to insert an <tt>Instruction</tt>
+into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
+
+<ul>
+ <li>Insertion into an explicit instruction list
+
+ <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
+ <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
+ before <tt>*pi</tt>, we do the following: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
+</pre>
+</div>
+
+ <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
+ the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
+ classes provide constructors which take a pointer to a
+ <tt>BasicBlock</tt> to be appended to. For example code that
+ looked like: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(...);
+
+pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
+</pre>
+</div>
+
+ <p>becomes: </p>
+
+<div class="doc_code">
+<pre>
+BasicBlock *pb = ...;
+Instruction *newInst = new Instruction(..., pb);
+</pre>
+</div>
+
+ <p>which is much cleaner, especially if you are creating
+ long instruction streams.</p></li>
+
+ <li>Insertion into an implicit instruction list
+
+ <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
+ are implicitly associated with an existing instruction list: the instruction
+ list of the enclosing basic block. Thus, we could have accomplished the same
+ thing as the above code without being given a <tt>BasicBlock</tt> by doing:
+ </p>
+
+<div class="doc_code">
+<pre>
+Instruction *pi = ...;
+Instruction *newInst = new Instruction(...);
+
+pi->getParent()->getInstList().insert(pi, newInst);
+</pre>
+</div>
+
+ <p>In fact, this sequence of steps occurs so frequently that the
+ <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
+ constructors which take (as a default parameter) a pointer to an
+ <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
+ precede. That is, <tt>Instruction</tt> constructors are capable of
+ inserting the newly-created instance into the <tt>BasicBlock</tt> of a
+ provided instruction, immediately before that instruction. Using an
+ <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
+ parameter, the above code becomes:</p>
+
+<div class="doc_code">
+<pre>
+Instruction* pi = ...;
+Instruction* newInst = new Instruction(..., pi);
+</pre>
+</div>
+
+ <p>which is much cleaner, especially if you're creating a lot of
+ instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
+</ul>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
+</div>
+
+<div class="doc_text">
+
+<p>Deleting an instruction from an existing sequence of instructions that form a
+<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
+you must have a pointer to the instruction that you wish to delete. Second, you
+need to obtain the pointer to that instruction's basic block. You use the
+pointer to the basic block to get its list of instructions and then use the
+erase function to remove your instruction. For example:</p>
+
+<div class="doc_code">
+<pre>
+<a href="#Instruction">Instruction</a> *I = .. ;
+I->eraseFromParent();
+</pre>
+</div>
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
+ <tt>Value</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p><i>Replacing individual instructions</i></p>
+
+<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
+permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
+and <tt>ReplaceInstWithInst</tt>.</p>
+
+<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
+
+<ul>
+ <li><tt>ReplaceInstWithValue</tt>
+
+ <p>This function replaces all uses (within a basic block) of a given
+ instruction with a value, and then removes the original instruction. The
+ following example illustrates the replacement of the result of a particular
+ <tt>AllocaInst</tt> that allocates memory for a single integer with a null
+ pointer to an integer.</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
+ Constant::getNullValue(PointerType::get(Type::Int32Ty)));
+</pre></div></li>
+
+ <li><tt>ReplaceInstWithInst</tt>
+
+ <p>This function replaces a particular instruction with another
+ instruction. The following example illustrates the replacement of one
+ <tt>AllocaInst</tt> with another.</p>
+
+<div class="doc_code">
+<pre>
+AllocaInst* instToReplace = ...;
+BasicBlock::iterator ii(instToReplace);
+
+ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
+ new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
+</pre></div></li>
+</ul>
+
+<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
+
+<p>You can use <tt>Value::replaceAllUsesWith</tt> and
+<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
+doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
+and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
+information.</p>
+
+<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
+include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
+ReplaceInstWithValue, ReplaceInstWithInst -->
+
+</div>
+
+<!--_______________________________________________________________________-->
+<div class="doc_subsubsection">
+ <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
+</div>
+
+<div class="doc_text">
+
+<p>Deleting a global variable from a module is just as easy as deleting an
+Instruction. First, you must have a pointer to the global variable that you wish
+ to delete. You use this pointer to erase it from its parent, the module.
+ For example:</p>
+
+<div class="doc_code">
+<pre>
+<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
+
+GV->eraseFromParent();
+</pre>
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="advanced">Advanced Topics</a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+<p>
+This section describes some of the advanced or obscure API's that most clients
+do not need to be aware of. These API's tend manage the inner workings of the
+LLVM system, and only need to be accessed in unusual circumstances.
+</p>
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="TypeResolve">LLVM Type Resolution</a>
+</div>
+
+<div class="doc_text">
+
+<p>
+The LLVM type system has a very simple goal: allow clients to compare types for
+structural equality with a simple pointer comparison (aka a shallow compare).
+This goal makes clients much simpler and faster, and is used throughout the LLVM
+system.
+</p>
+
+<p>
+Unfortunately achieving this goal is not a simple matter. In particular,
+recursive types and late resolution of opaque types makes the situation very
+difficult to handle. Fortunately, for the most part, our implementation makes
+most clients able to be completely unaware of the nasty internal details. The
+primary case where clients are exposed to the inner workings of it are when
+building a recursive type. In addition to this case, the LLVM bitcode reader,
+assembly parser, and linker also have to be aware of the inner workings of this
+system.
+</p>
+
+<p>
+For our purposes below, we need three concepts. First, an "Opaque Type" is
+exactly as defined in the <a href="LangRef.html#t_opaque">language
+reference</a>. Second an "Abstract Type" is any type which includes an
+opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
+Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
+float }</tt>").
+</p>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="BuildRecType">Basic Recursive Type Construction</a>
+</div>
+
+<div class="doc_text">
+
+<p>
+Because the most common question is "how do I build a recursive type with LLVM",
+we answer it now and explain it as we go. Here we include enough to cause this
+to be emitted to an output .ll file:
+</p>
+
+<div class="doc_code">
+<pre>
+%mylist = type { %mylist*, i32 }
+</pre>
+</div>
+
+<p>
+To build this, use the following LLVM APIs:
+</p>
+
+<div class="doc_code">
+<pre>
+// <i>Create the initial outer struct</i>
+<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
+std::vector<const Type*> Elts;
+Elts.push_back(PointerType::get(StructTy));
+Elts.push_back(Type::Int32Ty);
+StructType *NewSTy = StructType::get(Elts);
+
+// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
+// <i>the struct and the opaque type are actually the same.</i>
+cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
+
+// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
+// <i>kept up-to-date</i>
+NewSTy = cast<StructType>(StructTy.get());
+
+// <i>Add a name for the type to the module symbol table (optional)</i>
+MyModule->addTypeName("mylist", NewSTy);
+</pre>
+</div>
+
+<p>
+This code shows the basic approach used to build recursive types: build a
+non-recursive type using 'opaque', then use type unification to close the cycle.
+The type unification step is performed by the <tt><a
+href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
+described next. After that, we describe the <a
+href="#PATypeHolder">PATypeHolder class</a>.
+</p>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
+</div>
+
+<div class="doc_text">
+<p>
+The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
+While this method is actually a member of the DerivedType class, it is most
+often used on OpaqueType instances. Type unification is actually a recursive
+process. After unification, types can become structurally isomorphic to
+existing types, and all duplicates are deleted (to preserve pointer equality).
+</p>
+
+<p>
+In the example above, the OpaqueType object is definitely deleted.
+Additionally, if there is an "{ \2*, i32}" type already created in the system,
+the pointer and struct type created are <b>also</b> deleted. Obviously whenever
+a type is deleted, any "Type*" pointers in the program are invalidated. As
+such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
+live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
+types can never move or be deleted). To deal with this, the <a
+href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
+reference to a possibly refined type, and the <a
+href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
+complex datastructures.
+</p>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="PATypeHolder">The PATypeHolder Class</a>
+</div>
+
+<div class="doc_text">
+<p>
+PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
+happily goes about nuking types that become isomorphic to existing types, it
+automatically updates all PATypeHolder objects to point to the new type. In the
+example above, this allows the code to maintain a pointer to the resultant
+resolved recursive type, even though the Type*'s are potentially invalidated.
+</p>
+
+<p>
+PATypeHolder is an extremely light-weight object that uses a lazy union-find
+implementation to update pointers. For example the pointer from a Value to its
+Type is maintained by PATypeHolder objects.
+</p>
+
+</div>
+
+<!-- ______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
+</div>
+
+<div class="doc_text">
+
+<p>
+Some data structures need more to perform more complex updates when types get
+resolved. To support this, a class can derive from the AbstractTypeUser class.
+This class
+allows it to get callbacks when certain types are resolved. To register to get
+callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
+methods can be called on a type. Note that these methods only work for <i>
+ abstract</i> types. Concrete types (those that do not include any opaque
+objects) can never be refined.
+</p>
+</div>
+
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
+ <tt>TypeSymbolTable</tt> classes</a>
+</div>
+
+<div class="doc_text">
+<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
+ValueSymbolTable</a></tt> class provides a symbol table that the <a
+href="#Function"><tt>Function</tt></a> and <a href="#Module">
+<tt>Module</tt></a> classes use for naming value definitions. The symbol table
+can provide a name for any <a href="#Value"><tt>Value</tt></a>.
+The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
+TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
+names for types.</p>
+
+<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
+by most clients. It should only be used when iteration over the symbol table
+names themselves are required, which is very special purpose. Note that not
+all LLVM
+<a href="#Value">Value</a>s have names, and those without names (i.e. they have
+an empty name) do not exist in the symbol table.
+</p>
+
+<p>These symbol tables support iteration over the values/types in the symbol
+table with <tt>begin/end/iterator</tt> and supports querying to see if a
+specific name is in the symbol table (with <tt>lookup</tt>). The
+<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
+simply call <tt>setName</tt> on a value, which will autoinsert it into the
+appropriate symbol table. For types, use the Module::addTypeName method to
+insert entries into the symbol table.</p>
+
+</div>
+
+
+
+<!-- *********************************************************************** -->
+<div class="doc_section">
+ <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
+</div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
+<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
+
+<p>The Core LLVM classes are the primary means of representing the program
+being inspected or transformed. The core LLVM classes are defined in
+header files in the <tt>include/llvm/</tt> directory, and implemented in
+the <tt>lib/VMCore</tt> directory.</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="Type">The <tt>Type</tt> class and Derived Types</a>
+</div>
+
+<div class="doc_text">