Hi, RFC Im adding 2 new functions to the AliasAnalysis interface: 1) ModRefSameBufferCheck: this function will receive 2 memoryLocation as parameters, and returns true if the parameters are modifying or refering the same buffer or same memory block, false otherwise. 2) getAddressesDistance: the function will recieve 2 memoryLocation, if they are mod/ref-ing the same buffer/memory block, the function will return the distance between those locations at the memory. None otherwise (Optional<int64_t>) interface change: [https://reviews.llvm.org/D46864](https://reviews.llvm.org/D46864) those 2 function can be impelemented easly in AlisAnalysis and can help alot of users, a usage example is for detecting bank conflicts (using the distance between memoryLoc and the number and size of the banks you can know if you have a conflict). implementation and usage example (with code duplication for a first implementation, lets discuss the idea first): [https://reviews.llvm.org/D46928](https://reviews.llvm.org/D46928) I saw one bad implemntation for detecting bank conflicts in Hexagon open-source, but it wont realy work for most of examples, they only check if the registers are equal.. in my implamentation I check the real distance between locations... thanks, Atheel Massalha Compiler Engineer
I’m not completely sure what “same buffer” means; is it just that given MemoryLocations with addresses A and B, an offset N exists such that gep(A,N) is mustalias with B? What happens if alias can’t prove whether the two locations point to the “same buffer”? Is that actually the property you care about? DependenceAnalysis would probably be more appropriate if you’re trying to analyze cross-iteration dependencies in loops. Could you implement this by just calling alias() with the sizes set to UnknownSize? If I’m following correctly, given two values A and B, if a small constant offset N is known such that A+N==B, N is returned; if the distance is unknown or not a constant, None is returned. Not sure why the API takes memoryLocations, instead of just two Value*. Not sure this really belongs in AliasAnalysis. -Eli
thanks for your reply,
what is Im trying to analyze is the 2 memory instructions are using the same “Bank” of memory, Bank is a column in the physical memory rows of a memory block, for that I need to known if 2 instructions are using same block (usually, 2 different arrays are mapped to different blocks, but for [int* a=b+1], ‘a’ and ‘b’ will be in the same block, do oyu mean that “unkownSize” will always return “mayAlias”/“noAlias” for same/different blocks? sounds good idea, I will try it.
true. because it needs the size and the pointerInfo
another use fir this 2 interfaces is for “merging” load instructions registers, as for today, LLVM generates different register names for ld instructions with same base pointer but different offset, this can be optimized using the knowledge of the distance between them.
*any suggestions for improving this?
sorry for the late response,