diff options
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 56ad856b167..584290bd0fc 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -571,6 +571,11 @@ MachineBlockPlacement::findBestLoopTop(MachineFunction &F, BlockFrequency BestExitEdgeFreq; MachineBasicBlock *ExitingBB = 0; MachineBasicBlock *LoopingBB = 0; + // If there are exits to outer loops, loop rotation can severely limit + // fallthrough opportunites unless it selects such an exit. Keep a set of + // blocks where rotating to exit with that block will reach an outer loop. + SmallPtrSet<MachineBasicBlock *, 4> BlocksExitingToOuterLoop; + DEBUG(dbgs() << "Finding best loop exit for: " << getBlockName(L.getHeader()) << "\n"); for (MachineLoop::block_iterator I = L.block_begin(), @@ -641,6 +646,10 @@ MachineBlockPlacement::findBestLoopTop(MachineFunction &F, BestExitEdgeFreq = ExitEdgeFreq; ExitingBB = *I; } + + if (MachineLoop *ExitLoop = MLI->getLoopFor(*SI)) + if (ExitLoop->contains(&L)) + BlocksExitingToOuterLoop.insert(*I); } // Restore the old exiting state, no viable looping successor was found. @@ -659,6 +668,13 @@ MachineBlockPlacement::findBestLoopTop(MachineFunction &F, if (!ExitingBB || L.getNumBlocks() == 1) return L.getHeader(); + // Also, if we have exit blocks which lead to outer loops but didn't select + // one of them as the exiting block we are rotating toward, disable loop + // rotation altogether. + if (!BlocksExitingToOuterLoop.empty() && + !BlocksExitingToOuterLoop.count(ExitingBB)) + return L.getHeader(); + assert(LoopingBB && "All successors of a loop block are exit blocks!"); DEBUG(dbgs() << " Best exiting block: " << getBlockName(ExitingBB) << "\n"); DEBUG(dbgs() << " Best top block: " << getBlockName(LoopingBB) << "\n"); |
