[LLVMdev] Adding variants of some instructions

[Hans Vandierendonck]

Hi,

I need to have special variants of some instructions, e.g. a special  
MallocInst that carries some additional information. Besides having  
this additional information, I want all of LLVM to recognize this  
instruction as a regular MallocInst. This special MallocInst need only  
exist inside LLVM; it need not be written out to bytecode. How to best  
implement this?

This is what I was thinking:
* Not to introduce a new instruction, but to represent special  
MallocInst as a derived class from MallocInst
* Introduce the special MallocInst instructions during a pass that  
decides to replace some original MallocInsts or some other code by  
special MallocInst
* Apply LLVM analysis and transformations assuming that when new  
MallocInsts are created, the proper clone() function is called
* Apply my own passes that use the special MallocInst. This requires  
to recognize that some MallocInst are special MallocInst, but the  
isa<> interface won't be usable for that
* Revert the special MallocInst instructions to whatever code was  
there before

Is this a good approach or are there better alternatives?

Thanks for the help
Hans Vandierendonck.