diff options
Diffstat (limited to 'llvm/lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 17 |
1 files changed, 13 insertions, 4 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 4b0f7f3..00a3099 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -58,6 +58,13 @@ static cl::opt<unsigned> AlignAllBlock("align-all-blocks", "blocks in the function."), cl::init(0), cl::Hidden); +// FIXME: Find a good default for this flag and remove the flag. +static cl::opt<unsigned> +ExitBlockBias("block-placement-exit-block-bias", + cl::desc("Block frequency percentage a loop exit block needs " + "over the original exit to be considered the new exit."), + cl::init(0), cl::Hidden); + namespace { class BlockChain; /// \brief Type for our function-wide basic block -> block chain mapping. @@ -691,13 +698,15 @@ MachineBlockPlacement::findBestLoopExit(MachineFunction &F, DEBUG(dbgs() << " exiting: " << getBlockName(*I) << " -> " << getBlockName(*SI) << " [L:" << SuccLoopDepth << "] (" << ExitEdgeFreq << ")\n"); - // Note that we slightly bias this toward an existing layout successor to - // retain incoming order in the absence of better information. - // FIXME: Should we bias this more strongly? It's pretty weak. + // Note that we bias this toward an existing layout successor to retain + // incoming order in the absence of better information. The exit must have + // a frequency higher than the current exit before we consider breaking + // the layout. + BranchProbability Bias(100 - ExitBlockBias, 100); if (!ExitingBB || BestExitLoopDepth < SuccLoopDepth || ExitEdgeFreq > BestExitEdgeFreq || ((*I)->isLayoutSuccessor(*SI) && - !(ExitEdgeFreq < BestExitEdgeFreq))) { + !(ExitEdgeFreq < BestExitEdgeFreq * Bias))) { BestExitEdgeFreq = ExitEdgeFreq; ExitingBB = *I; } |