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author | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2013-07-01 23:36:37 +0000 |
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committer | Jakob Stoklund Olesen <stoklund@2pi.dk> | 2013-07-01 23:36:37 +0000 |
commit | 7babb052a68a35a7b21906280e67f06502846f9d (patch) | |
tree | fedc0aeaee5df4772f66fd160351a5fbce0e1397 /lib/CodeGen/SpillPlacement.cpp | |
parent | 228e0afcfd0d5f167a95c6ddbec2c6a4a90b6d2b (diff) | |
download | llvm-7babb052a68a35a7b21906280e67f06502846f9d.tar.gz llvm-7babb052a68a35a7b21906280e67f06502846f9d.tar.bz2 llvm-7babb052a68a35a7b21906280e67f06502846f9d.tar.xz |
Tweak some comments that referred to the old bias computations.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185395 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen/SpillPlacement.cpp')
-rw-r--r-- | lib/CodeGen/SpillPlacement.cpp | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/lib/CodeGen/SpillPlacement.cpp b/lib/CodeGen/SpillPlacement.cpp index 8fda626ef5..10a93b7fa4 100644 --- a/lib/CodeGen/SpillPlacement.cpp +++ b/lib/CodeGen/SpillPlacement.cpp @@ -79,17 +79,14 @@ struct SpillPlacement::Node { BlockFrequency BiasP; /// Value - Output value of this node computed from the Bias and links. - /// This is always in the range [-1;1]. A positive number means the variable - /// should go in a register through this bundle. + /// This is always on of the values {-1, 0, 1}. A positive number means the + /// variable should go in a register through this bundle. int Value; typedef SmallVector<std::pair<BlockFrequency, unsigned>, 4> LinkVector; /// Links - (Weight, BundleNo) for all transparent blocks connecting to other - /// bundles. The weights are all positive and add up to at most 2, weights - /// from ingoing and outgoing nodes separately add up to a most 1. The weight - /// sum can be less than 2 when the variable is not live into / out of some - /// connected basic blocks. + /// bundles. The weights are all positive block frequencies. LinkVector Links; /// SumLinkWeights - Cached sum of the weights of all links + ThresHold. @@ -162,12 +159,14 @@ struct SpillPlacement::Node { SumP += I->first; } - // The weighted sum is going to be in the range [-2;2]. Ideally, we should - // simply set Value = sign(Sum), but we will add a dead zone around 0 for - // two reasons: + // Each weighted sum is going to be less than the total frequency of the + // bundle. Ideally, we should simply set Value = sign(SumP - SumN), but we + // will add a dead zone around 0 for two reasons: + // // 1. It avoids arbitrary bias when all links are 0 as is possible during // initial iterations. // 2. It helps tame rounding errors when the links nominally sum to 0. + // bool Before = preferReg(); if (SumN >= SumP + Threshold) Value = -1; @@ -215,10 +214,11 @@ void SpillPlacement::activate(unsigned n) { // landing pads, or loops with many 'continue' statements. It is difficult to // allocate registers when so many different blocks are involved. // - // Give a small negative bias to large bundles such that 1/32 of the - // connected blocks need to be interested before we consider expanding the - // region through the bundle. This helps compile time by limiting the number - // of blocks visited and the number of links in the Hopfield network. + // Give a small negative bias to large bundles such that a substantial + // fraction of the connected blocks need to be interested before we consider + // expanding the region through the bundle. This helps compile time by + // limiting the number of blocks visited and the number of links in the + // Hopfield network. if (bundles->getBlocks(n).size() > 100) { nodes[n].BiasP = 0; nodes[n].BiasN = (BlockFrequency::getEntryFrequency() / 16); |