Chandler Carruth ed90ed077a Add a new visitor for walking the uses of a pointer value. ... This visitor provides infrastructure for recursively traversing the use-graph of a pointer-producing instruction like an alloca or a malloc. It maintains a worklist of uses to visit, so it can handle very deep recursions. It automatically looks through instructions which simply translate one pointer to another (bitcasts and GEPs). It tracks the offset relative to the original pointer as long as that offset remains constant and exposes it during the visit as an APInt offset. Finally, it performs conservative escape analysis. However, currently it has some limitations that should be addressed going forward: 1) It doesn't handle vectors of pointers. 2) It doesn't provide a cheaper visitor when the constant offset tracking isn't needed. 3) It doesn't support non-instruction pointer values. The current functionality is exactly what is required to implement the SROA pointer-use visitors in terms of this one, rather than in terms of their own ad-hoc base visitor, which was always very poorly specified. SROA has been converted to use this, and the code there deleted which this utility now provides. Technically speaking, using this new visitor allows SROA to handle a few more cases than it previously did. It is now more aggressive in ignoring chains of instructions which look like they would defeat SROA, but in fact do not because they never result in a read or write of memory. While this is "neat", it shouldn't be interesting for real programs as any such chains should have been removed by others passes long before we get to SROA. As a consequence, I've not added any tests for these features -- it shouldn't be part of SROA's contract to perform such heroics. The goal is to extend the functionality of this visitor going forward, and re-use it from passes like ASan that can benefit from doing a detailed walk of the uses of a pointer. Thanks to Ben Kramer for the code review rounds and lots of help reviewing and debugging this patch. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169728 91177308-0d34-0410-b5e6-96231b3b80d8		2012-12-10 08:28:39 +00:00
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llvm	Add a new visitor for walking the uses of a pointer value.	2012-12-10 08:28:39 +00:00
llvm-c	Add the `lto_codegen_set_export_dynamic' function.	2012-12-08 00:18:16 +00:00