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division and make the private scale in BlockFrequency more performant.
This change is the first in a series of changes improving LLVM's Block
Frequency propogation implementation to not lose probability mass in
branchy code when propogating block frequency information from a basic
block to its successors. This patch is a simple infrastructure
improvement that does not actually modify the block frequency
algorithm. The specific changes are:
1. Changes the division algorithm used when scaling block frequencies by
branch probabilities to a short division algorithm. This gives us the
remainder for free as well as provides a nice speed boost. When I
benched the old routine and the new routine on a Sandy Bridge iMac with
disabled turbo mode performing 8192 iterations on an array of length
32768, I saw ~600% increase in speed in mean/median performance.
2. Exposes a scale method that returns a remainder. This is important so
we can ensure that when we scale a block frequency by some branch
probability BP = N/D, the remainder from the division by D can be
retrieved and propagated to other children to ensure no probability mass
is lost (more to come on this).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194950 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185226 91177308-0d34-0410-b5e6-96231b3b80d8
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Hopefully, this fixes the PPC64 buildbots.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185218 91177308-0d34-0410-b5e6-96231b3b80d8
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- Use static functions instead of anonymous namespace.
- Appease the Doxygen lobby.
- Use 0-based induction variable.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185185 91177308-0d34-0410-b5e6-96231b3b80d8
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Allow a BlockFrequency to be divided by a non-zero BranchProbability
with saturating arithmetic. This will be used to compute the frequency
of a loop header given the probability of leaving the loop.
Our long division algorithm already saturates on overflow, so that was a
freebie.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185184 91177308-0d34-0410-b5e6-96231b3b80d8
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This is easier to read than the internal fixed-point representation.
If anybody knows the correct algorithm for converting fixed-point
numbers to base 10, feel free to fix it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184881 91177308-0d34-0410-b5e6-96231b3b80d8
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frequency with a branch probability."
This reverts commit r184584. Breaks PPC selfhost.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184590 91177308-0d34-0410-b5e6-96231b3b80d8
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a branch probability.
Zero is used by BlockFrequencyInfo as a special "don't know" value. It also
causes a sink for frequencies as you can't ever get off a zero frequency with
more multiplies.
This recovers a 10% regression on MultiSource/Benchmarks/7zip. A zero frequency
was propagated into an inner loop causing excessive spilling.
PR16402.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184584 91177308-0d34-0410-b5e6-96231b3b80d8
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This trades one 64 bit div for one 64 bit mul and some arithmetic.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143106 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136222 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136221 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135992 91177308-0d34-0410-b5e6-96231b3b80d8
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