文档地址：
http://llvm.org/docs/ProgrammersManual.html
The isa<> operator works exactly like the Java "instanceof" operator. It returns true or false depending on whether a reference or pointer points to an instance of the specified class.
The cast<> operator is a "checked cast" operation. It converts a pointer or reference from a base class to a derived class, causing an assertion failure if it is not really an instance of the right type.
The dyn_cast<> operator is a "checking cast" operation. It checks to see if the operand is of the specified type, and if so, returns a pointer to it (this operator does not work with references). If the operand is not of the correct type, a null
pointer is returned.
passing strings efficiently.
the common operations available on std:string, but does not require heap allocation.
The Statistic class & -stats option
The "llvm/ADT/Statistic.h" file provides a class named Statistic that is used as a unified way to keep track of what the LLVM compiler is doing and how effective various optimizations are. It is useful to see what optimizations are contributing to making a
particular program run faster.
Turning an iterator into a class pointer (and vice-versa)
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). It's also possible to turn a class pointer into the corresponding iterator, and this is a constant time operation (very efficient).
Function *F = ...;
for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
errs() << "F is used in instruction:\n";
errs() << *Inst << "\n";
}
Instruction *pi = ...;
for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
Value *v = *i;
// ...
}
其实这个文档的目的比较简单，就是介绍一些常用的API和类。虽然在用的时候会发现，这些介绍的东西在LLVM所有的类和API中就是九牛一毛，但是有总胜于无。在实际的编码过程中，只能依赖的就是源码。所以，读源码是必不可少的。