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Summary: This is part 1 of fixes to address the problems described in https://llvm.org/bugs/show_bug.cgi?id=22719. The restriction to limit loop scales to 4,096 does not really prevent overflows anymore, as the underlying algorithm has changed and does not seem to suffer from this problem. Additionally, artificially restricting loop scales to such a low number skews frequency information, making loops of equal hotness appear to have very different hotness properties. The only loops that are artificially restricted to a scale of 4096 are infinite loops (those loops with an exit mass of 0). This prevents infinite loops from skewing the frequencies of other regions in the CFG. At the end of propagation, frequencies are scaled to values that take no more than 64 bits to represent. When the range of frequencies to be represented fits within 61 bits, it pushes up the scaling factor to a minimum of 8 to better distinguish small frequency values. Otherwise, small frequency values are all saturated down at 1. Tested on x86_64. Reviewers: dexonsmith Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D8718 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233826 91177308-0d34-0410-b5e6-96231b3b80d8
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