diff options
Diffstat (limited to 'llvm/lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 06cc7ba..86a4922 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -74,6 +74,12 @@ static cl::opt<bool> OutlineOptionalBranches( "post dominator, out of line."), cl::init(false), cl::Hidden); +static cl::opt<unsigned> OutlineOptionalThreshold( + "outline-optional-threshold", + cl::desc("Don't outline optional branches that are a single block with an " + "instruction count below this threshold"), + cl::init(4), cl::Hidden); + namespace { class BlockChain; /// \brief Type for our function-wide basic block -> block chain mapping. @@ -377,8 +383,25 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB, // dominates all terminators of the MachineFunction. If it does, other // successors must be optional. Don't do this for cold branches. if (OutlineOptionalBranches && SuccProb > HotProb.getCompl() && - UnavoidableBlocks.count(Succ) > 0) - return Succ; + UnavoidableBlocks.count(Succ) > 0) { + auto HasShortOptionalBranch = [&]() { + for (MachineBasicBlock *Pred : Succ->predecessors()) { + // Check whether there is an unplaced optional branch. + if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) || + BlockToChain[Pred] == &Chain) + continue; + // Check whether the optional branch has exactly one BB. + if (Pred->pred_size() > 1 || *Pred->pred_begin() != BB) + continue; + // Check whether the optional branch is small. + if (Pred->size() < OutlineOptionalThreshold) + return true; + } + return false; + }; + if (!HasShortOptionalBranch()) + return Succ; + } // Only consider successors which are either "hot", or wouldn't violate // any CFG constraints. |