Previously, BranchProbabilityInfo::calcLoopBranchHeuristics would determine the weights of basic blocks inside loops even when it didn't have enough information to estimate the branch probabilities correctly. This patch fixes the function to exit early if it doesn't see any exit edges or back edges and let the later heuristics determine the weights.
This fixes PR18705 and <rdar://problem/15991090>.
Differential Revision: http://reviews.llvm.org/D3363
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206194 91177308-0d34-0410-b5e6-96231b3b80d8
classifying many edges as exiting which were in fact not. These mainly
formed edges into sub-loops. It was also not correctly classifying all
returning edges out of loops as leaving the loop. With this match most
of the loop heuristics are more rational.
Several serious regressions on loop-intesive benchmarks like perlbench's
loop tests when built with -enable-block-placement are fixed by these
updated heuristics. Unfortunately they in turn uncover some other
regressions. There are still several improvemenst that should be made to
loop heuristics including trip-count, and early back-edge management.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142917 91177308-0d34-0410-b5e6-96231b3b80d8
