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Update a bunch of stale comments that dated from when this folled the

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very first (and worst) placement algorithm. These should now more
accurately reflect the reality of the pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159185 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2012-06-26 05:16:37 +00:00
parent 952caee4f6
commit c04f816afd
1 changed files with 11 additions and 14 deletions
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25
lib/CodeGen/MachineBlockPlacement.cpp
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@ -63,17 +63,13 @@ namespace {
/// ///
/// This is the datastructure representing a chain of consecutive blocks that /// This is the datastructure representing a chain of consecutive blocks that
/// are profitable to layout together in order to maximize fallthrough /// are profitable to layout together in order to maximize fallthrough
/// probabilities. We also can use a block chain to represent a sequence of /// probabilities and code locality. We also can use a block chain to represent
/// basic blocks which have some external (correctness) requirement for /// a sequence of basic blocks which have some external (correctness)
/// sequential layout. /// requirement for sequential layout.
/// ///
/// Eventually, the block chains will form a directed graph over the function. /// Chains can be built around a single basic block and can be merged to grow
/// We provide an SCC-supporting-iterator in order to quicky build and walk the /// them. They participate in a block-to-chain mapping, which is updated
/// SCCs of block chains within a function. /// automatically as chains are merged together.
///
/// The block chains also have support for calculating and caching probability
/// information related to the chain itself versus other chains. This is used
/// for ranking during the final layout of block chains.
class BlockChain { class BlockChain {
/// \brief The sequence of blocks belonging to this chain. /// \brief The sequence of blocks belonging to this chain.
/// ///
@ -179,10 +175,11 @@ class MachineBlockPlacement : public MachineFunctionPass {
/// \brief Allocator and owner of BlockChain structures. /// \brief Allocator and owner of BlockChain structures.
/// ///
/// We build BlockChains lazily by merging together high probability BB /// We build BlockChains lazily while processing the loop structure of
/// sequences according to the "Algo2" in the paper mentioned at the top of /// a function. To reduce malloc traffic, we allocate them using this
/// the file. To reduce malloc traffic, we allocate them using this slab-like /// slab-like allocator, and destroy them after the pass completes. An
/// allocator, and destroy them after the pass completes. /// important guarantee is that this allocator produces stable pointers to
/// the chains.
SpecificBumpPtrAllocator<BlockChain> ChainAllocator; SpecificBumpPtrAllocator<BlockChain> ChainAllocator;
/// \brief Function wide BasicBlock to BlockChain mapping. /// \brief Function wide BasicBlock to BlockChain mapping.