[PATCH] Introduce bitset metadata format and bitset lowering pass.

[Kostya Serebryany]

Few comments in random places, more to go


================
Comment at: lib/Transforms/IPO/LowerBitSets.cpp:10
@@ +9,3 @@
+//
+// This pass lowers bitset metadata and calls to the llvm.bitset.test intrinsic.
+// See http://llvm.org/docs/LangRef.html#bitsets for more information.
----------------
are we going to handle InvokeInst?
Check llvm/IR/CallSite.h

================
Comment at: lib/Transforms/IPO/LowerBitSets.cpp:55
@@ +54,3 @@
+  // Mapping from bitset mdstrings to the call sites that test them.
+  DenseMap<MDString *, std::vector<CallInst *>> BitSetTestCallSites;
+
----------------
SmallVector maybe

================
Comment at: lib/Transforms/IPO/LowerBitSets.cpp:106
@@ +105,3 @@
+  if (DL)
+    IntPtrTy = DL->getIntPtrType(M.getContext(), 0);
+
----------------
I'd prefer if we report_fatal_error w/o DL, just like in AddressSanitizer.cpp

http://reviews.llvm.org/D7288

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