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73 lines
3.4 KiB
73 lines
3.4 KiB
4 months ago
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Changes:
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* Change the casting code to be const correct. Now, doing this is invalid:
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const Value *V = ...;
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Instruction *I = dyn_cast<Instruction>(V);
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instead, the second line should be:
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const Instruction *I = dyn_cast<Instruction>(V);
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* Change the casting code to allow casting a reference value thus:
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const Value &V = ...;
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Instruction &I = cast<Instruction>(V);
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dyn_cast does not work with references, because it must return a null pointer
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on failure.
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* Fundamentally change how instructions and other values are represented.
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Before, every llvm container was an instance of the ValueHolder template,
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instantiated for each container type. This ValueHolder was effectively a
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wrapper around a vector of pointers to the sub-objects.
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Now, instead of having a vector to pointers of objects, the objects are
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maintained in a doubly linked list of values (ie each Instruction now has
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Next & Previous fields). The containers are now instances of ilist (intrusive
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linked list class), which use the next and previous fields to chain them
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together. The advantage of this implementation is that iterators can be
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formed directly from pointers to the LLVM value, and invalidation is much
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easier to handle.
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* As part of the above change, dereferencing an iterator (for example:
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BasicBlock::iterator) now produces a reference to the underlying type (same
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example: Instruction&) instead of a pointer to the underlying object. This
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makes it much easier to write nested loops that iterator over things, changing
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this:
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for (Function::iterator BI = Func->begin(); BI != Func->end(); ++BI)
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for (BasicBlock::iterator II = (*BI)->begin(); II != (*BI)->end(); ++II)
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(*II)->dump();
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into:
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for (Function::iterator BI = Func->begin(); BI != Func->end(); ++BI)
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for (BasicBlock::iterator II = BI->begin(); II != BI->end(); ++II)
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II->dump();
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which is much more natural and what users expect.
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* Simplification of #include's: Before, it was necessary for a .cpp file to
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include every .h file that it used. Now things are batched a little bit more
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to make it easier to use. Specifically, the include graph now includes these
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edges:
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Module.h -> Function.h, GlobalVariable.h
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Function.h -> BasicBlock.h, Argument.h
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BasicBlock.h -> Instruction.h
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Which means that #including Function.h is usually sufficient for getting the
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lower level #includes.
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* Printing out a Value* has now changed: Printing a Value* will soon print out
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the address of the value instead of the contents of the Value. To print out
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the contents, you must convert it to a reference with (for example)
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'cout << *I' instead of 'cout << I;'. This conversion is not yet complete,
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but will be eventually. In the mean time, both forms print out the contents.
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* References are used much more throughout the code base. In general, if a
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pointer is known to never be null, it is passed in as a reference instead of a
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pointer. For example, the instruction visitor class uses references instead
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of pointers, and that Pass subclasses now all receive references to Values
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instead of pointers, because they may never be null.
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* The Function class now has helper functions for accessing the Arguments list.
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Instead of having to go through getArgumentList for simple things like
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iterator over the arguments, now the a*() methods can be used to access them.
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