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- Problem One program takes ~3min to compile under -O2. This happens after a certain function A is inlined ~700 times in a function B, inserting thousands of new BBs. This leads to 80% of the compilation time spent in GVN::processNonLocalLoad and MemoryDependenceAnalysis::getNonLocalPointerDependency, while searching for nonlocal information for basic blocks. Usually, to avoid spending a long time to process nonlocal loads, GVN bails out if it gets more than 100 deps as a result from MD->getNonLocalPointerDependency. However this only happens *after* all nonlocal information for BBs have been computed, which is the bottleneck in this scenario. For instance, there are 8280 times where getNonLocalPointerDependency returns deps with more than 100 bbs and from those, 600 times it returns more than 1000 blocks. - Solution Bail out early during the nonlocal info computation whenever we reach a specified threshold. This patch proposes a 100 BBs threshold, it also reduces the compile time from 3min to 23s. - Testing The test-suite presented no compile nor execution time regressions. Some numbers from my machine (x86_64 darwin): - 17s under -Oz (which avoids inlining). - 1.3s under -O1. - 2m51s under -O2 ToT *** 23s under -O2 w/ Result.size() > 100 - 1m54s under -O2 w/ Result.size() > 500 With NumResultsLimit = 100, GVN yields the same outcome as in the unlimited 3min version. http://reviews.llvm.org/D5532 rdar://problem/18188041 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218792 91177308-0d34-0410-b5e6-96231b3b80d8
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