Introduce bitset metadata format and bitset lowering pass.
This patch introduces a new mechanism that allows IR modules to co-operatively
build pointer sets corresponding to addresses within a given set of
globals. One particular use case for this is to allow a C++ program to
efficiently verify (at each call site) that a vtable pointer is in the set
of valid vtable pointers for the class or its derived classes. One way of
doing this is for a toolchain component to build, for each class, a bit set
that maps to the memory region allocated for the vtables, such that each 1
bit in the bit set maps to a valid vtable for that class, and lay out the
vtables next to each other, to minimize the total size of the bit sets.
The patch introduces a metadata format for representing pointer sets, an
'@llvm.bitset.test' intrinsic and an LTO lowering pass that lays out the globals
and builds the bitsets, and documents the new feature.
Differential Revision: http://reviews.llvm.org/D7288
llvm-svn: 230054
diff --git a/llvm/lib/Transforms/IPO/IPO.cpp b/llvm/lib/Transforms/IPO/IPO.cpp
index 1605efa..fcacec3 100644
--- a/llvm/lib/Transforms/IPO/IPO.cpp
+++ b/llvm/lib/Transforms/IPO/IPO.cpp
@@ -36,6 +36,7 @@
initializeLoopExtractorPass(Registry);
initializeBlockExtractorPassPass(Registry);
initializeSingleLoopExtractorPass(Registry);
+ initializeLowerBitSetsPass(Registry);
initializeMergeFunctionsPass(Registry);
initializePartialInlinerPass(Registry);
initializePruneEHPass(Registry);