Eli Friedman 88e2bac94d [MemorySSA] Fix exponential compile-time updating MemorySSA. ... MemorySSAUpdater::getPreviousDefRecursive is a recursive algorithm, for each block, it computes the previous definition for each predecessor, then takes those definitions and combines them. But currently it doesn't remember results which it already computed; this means it can visit the same block multiple times, which adds up to exponential time overall. To fix this, this patch adds a cache. If we computed the result for a block already, we don't need to visit it again because we'll come up with the same result. Well, unless we RAUW a MemoryPHI; in that case, the TrackingVH will be updated automatically. This matches the original source paper for this algorithm. The testcase isn't really a test for the bug, but it adds coverage for the case where tryRemoveTrivialPhi erases an existing PHI node. (It's hard to write a good regression test for a performance issue.) Differential Revision: https://reviews.llvm.org/D44715 llvm-svn: 328577		2018-03-26 19:52:54 +00:00
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llvm	[MemorySSA] Fix exponential compile-time updating MemorySSA.	2018-03-26 19:52:54 +00:00
llvm-c	Reapply Support layering fixes.	2018-03-21 17:31:49 +00:00