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16e2f0ef1a
We now only allow breaking source order if the exit block frequency is significantly higher than the other exit block. The actual bias is currently under a flag so the best cut-off can be found; the flag defaults to the old behavior. The idea is to get some benchmark coverage over different values for the flag and pick the best one. When we require the new frequency to be at least 20% higher than the old frequency I see a 5% speedup on zlib's deflate when compressing a random file on x86_64/westmere. Hal reported a small speedup on Fhourstones on a BG/Q and no regressions in the test suite. The test case is the full long_match function from zlib's deflate. I was reluctant to add it for previous tweaks to branch probabilities because it's large and potentially fragile, but changed my mind since it's an important use case and more likely to break with all the current work going into the PGO infrastructure. Differential Revision: http://llvm-reviews.chandlerc.com/D2202 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195265 91177308-0d34-0410-b5e6-96231b3b80d8
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