diff options
Diffstat (limited to 'llvm/lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 25 |
1 files changed, 11 insertions, 14 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 9ca0ad2e241..5a15f92a182 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -63,17 +63,13 @@ namespace { /// /// This is the datastructure representing a chain of consecutive blocks that /// are profitable to layout together in order to maximize fallthrough -/// probabilities. We also can use a block chain to represent a sequence of -/// basic blocks which have some external (correctness) requirement for -/// sequential layout. +/// probabilities and code locality. We also can use a block chain to represent +/// a sequence of basic blocks which have some external (correctness) +/// requirement for sequential layout. /// -/// Eventually, the block chains will form a directed graph over the function. -/// We provide an SCC-supporting-iterator in order to quicky build and walk the -/// SCCs of block chains within a function. -/// -/// 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. +/// Chains can be built around a single basic block and can be merged to grow +/// them. They participate in a block-to-chain mapping, which is updated +/// automatically as chains are merged together. class BlockChain { /// \brief The sequence of blocks belonging to this chain. /// @@ -179,10 +175,11 @@ class MachineBlockPlacement : public MachineFunctionPass { /// \brief Allocator and owner of BlockChain structures. /// - /// We build BlockChains lazily by merging together high probability BB - /// sequences according to the "Algo2" in the paper mentioned at the top of - /// the file. To reduce malloc traffic, we allocate them using this slab-like - /// allocator, and destroy them after the pass completes. + /// We build BlockChains lazily while processing the loop structure of + /// a function. To reduce malloc traffic, we allocate them using this + /// slab-like allocator, and destroy them after the pass completes. An + /// important guarantee is that this allocator produces stable pointers to + /// the chains. SpecificBumpPtrAllocator<BlockChain> ChainAllocator; /// \brief Function wide BasicBlock to BlockChain mapping. |
