forked from OSchip/llvm-project
18251842c6
An abstract call site is a wrapper that allows to treat direct, indirect, and callback calls the same. If an abstract call site represents a direct or indirect call site it behaves like a stripped down version of a normal call site object. The abstract call site can also represent a callback call, thus the fact that the initially called function (=broker) may invoke a third one (=callback callee). In this case, the abstract call side hides the middle man, hence the broker function. The result is a representation of the callback call, inside the broker, but in the context of the original instruction that invoked the broker. Again, there are up to three functions involved when we talk about callback call sites. The caller (1), which invokes the broker function. The broker function (2), that may or may not invoke the callback callee. And finally the callback callee (3), which is the target of the callback call. The abstract call site will handle the mapping from parameters to arguments depending on the semantic of the broker function. However, it is important to note that the mapping is often partial. Thus, some arguments of the call/invoke instruction are mapped to parameters of the callee while others are not. At the same time, arguments of the callback callee might be unknown, thus "null" if queried. This patch introduces also !callback metadata which describe how a callback broker maps from parameters to arguments. This metadata is directly created by clang for known broker functions, provided through source code attributes by the user, or later deduced by analyses. For motivation and additional information please see the corresponding talk (slides/video) https://llvm.org/devmtg/2018-10/talk-abstracts.html#talk20 as well as the LCPC paper http://compilers.cs.uni-saarland.de/people/doerfert/par_opt_lcpc18.pdf Differential Revision: https://reviews.llvm.org/D54498 llvm-svn: 351627 |
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