[PATCH] [asan] Speed up interesting alloca checks

[Kostya Serebryany]

This looks fine, but I would slightly prefer to compute the map beforehand instead of caching, if possible. 
I.e. instead of a map of  ProcessedAllocas have a set of InterestingAllocas that is computed in visitAllocaInst


================
Comment at: lib/Transforms/Instrumentation/AddressSanitizer.cpp:811
@@ +810,3 @@
+
+  if (PreviouslySeenAllocaInfo != ProcessedAllocas.end()) {
+    return PreviouslySeenAllocaInfo->getSecond();
----------------
we tend to not write {} in such cases

http://reviews.llvm.org/D8639

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