Author: tstellar Date: Tue May 29 15:55:51 2018 New Revision: 333474 URL: http://llvm.org/viewvc/llvm-project?rev=333474&view=rev Log: Merging r328884:
------------------------------------------------------------------------ r328884 | timshen | 2018-03-30 10:51:00 -0700 (Fri, 30 Mar 2018) | 19 lines [BlockPlacement] Disable block placement tail duplciation in structured CFG. Summary: Tail duplication easily breaks the structure of CFG, e.g. duplicating on a region entry. If the structure is intended to be preserved, then we may want to configure tail duplication, or disable it for structured CFG. From our benchmark results disabling it doesn't cause performance regression. Notice that this currently affects AMDGPU backend. In the next patch, I also plan to turn on requiresStructuredCFG for NVPTX. All unit tests still pass. Reviewers: jlebar, arsenm Subscribers: jholewinski, sanjoy, wdng, tpr, hiraditya, llvm-commits Differential Revision: https://reviews.llvm.org/D45008 ------------------------------------------------------------------------ Modified: llvm/branches/release_60/lib/CodeGen/MachineBlockPlacement.cpp Modified: llvm/branches/release_60/lib/CodeGen/MachineBlockPlacement.cpp URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_60/lib/CodeGen/MachineBlockPlacement.cpp?rev=333474&r1=333473&r2=333474&view=diff ============================================================================== --- llvm/branches/release_60/lib/CodeGen/MachineBlockPlacement.cpp (original) +++ llvm/branches/release_60/lib/CodeGen/MachineBlockPlacement.cpp Tue May 29 15:55:51 2018 @@ -513,6 +513,11 @@ public: bool runOnMachineFunction(MachineFunction &F) override; + bool allowTailDupPlacement() const { + assert(F); + return TailDupPlacement && !F->getTarget().requiresStructuredCFG(); + } + void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired<MachineBranchProbabilityInfo>(); AU.addRequired<MachineBlockFrequencyInfo>(); @@ -1018,7 +1023,7 @@ MachineBlockPlacement::getBestTrellisSuc MachineBasicBlock *Succ1 = BestA.Dest; MachineBasicBlock *Succ2 = BestB.Dest; // Check to see if tail-duplication would be profitable. - if (TailDupPlacement && shouldTailDuplicate(Succ2) && + if (allowTailDupPlacement() && shouldTailDuplicate(Succ2) && canTailDuplicateUnplacedPreds(BB, Succ2, Chain, BlockFilter) && isProfitableToTailDup(BB, Succ2, MBPI->getEdgeProbability(BB, Succ1), Chain, BlockFilter)) { @@ -1044,7 +1049,7 @@ MachineBlockPlacement::getBestTrellisSuc return Result; } -/// When the option TailDupPlacement is on, this method checks if the +/// When the option allowTailDupPlacement() is on, this method checks if the /// fallthrough candidate block \p Succ (of block \p BB) can be tail-duplicated /// into all of its unplaced, unfiltered predecessors, that are not BB. bool MachineBlockPlacement::canTailDuplicateUnplacedPreds( @@ -1493,7 +1498,7 @@ MachineBlockPlacement::selectBestSuccess if (hasBetterLayoutPredecessor(BB, Succ, SuccChain, SuccProb, RealSuccProb, Chain, BlockFilter)) { // If tail duplication would make Succ profitable, place it. - if (TailDupPlacement && shouldTailDuplicate(Succ)) + if (allowTailDupPlacement() && shouldTailDuplicate(Succ)) DupCandidates.push_back(std::make_tuple(SuccProb, Succ)); continue; } @@ -1702,7 +1707,7 @@ void MachineBlockPlacement::buildChain( auto Result = selectBestSuccessor(BB, Chain, BlockFilter); MachineBasicBlock* BestSucc = Result.BB; bool ShouldTailDup = Result.ShouldTailDup; - if (TailDupPlacement) + if (allowTailDupPlacement()) ShouldTailDup |= (BestSucc && shouldTailDuplicate(BestSucc)); // If an immediate successor isn't available, look for the best viable @@ -1724,7 +1729,7 @@ void MachineBlockPlacement::buildChain( // Placement may have changed tail duplication opportunities. // Check for that now. - if (TailDupPlacement && BestSucc && ShouldTailDup) { + if (allowTailDupPlacement() && BestSucc && ShouldTailDup) { // If the chosen successor was duplicated into all its predecessors, // don't bother laying it out, just go round the loop again with BB as // the chain end. @@ -2758,7 +2763,7 @@ bool MachineBlockPlacement::runOnMachine TailDupSize = TailDupPlacementAggressiveThreshold; } - if (TailDupPlacement) { + if (allowTailDupPlacement()) { MPDT = &getAnalysis<MachinePostDominatorTree>(); if (MF.getFunction().optForSize()) TailDupSize = 1; _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
