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| author | Kyle Butt <kyle+llvm@iteratee.net> | 2017-01-11 19:55:19 +0000 |
|---|---|---|
| committer | Kyle Butt <kyle+llvm@iteratee.net> | 2017-01-11 19:55:19 +0000 |
| commit | efe56fed125ead532877ae87add255e0aa14db37 (patch) | |
| tree | c625d4b0981bfa75c68e4999ecbb0c48ac7609f5 /llvm/lib/CodeGen/MachineBlockPlacement.cpp | |
| parent | de782d16160dd7c0324c0759e29e5ca0a7460387 (diff) | |
| download | bcm5719-llvm-efe56fed125ead532877ae87add255e0aa14db37.tar.gz bcm5719-llvm-efe56fed125ead532877ae87add255e0aa14db37.zip | |
Revert "CodeGen: Allow small copyable blocks to "break" the CFG."
This reverts commit ada6595a526d71df04988eb0a4b4fe84df398ded.
This needs a simple probability check because there are some cases where it is
not profitable.
llvm-svn: 291695
Diffstat (limited to 'llvm/lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 59 |
1 files changed, 7 insertions, 52 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 42ae49283a6..40e3840e6b0 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -403,10 +403,6 @@ class MachineBlockPlacement : public MachineFunctionPass { void buildCFGChains(); void optimizeBranches(); void alignBlocks(); - bool shouldTailDuplicate(MachineBasicBlock *BB); - bool canTailDuplicateUnplacedPreds( - MachineBasicBlock *BB, MachineBasicBlock *Succ, - BlockChain &Chain, const BlockFilterSet *BlockFilter); public: static char ID; // Pass identification, replacement for typeid @@ -565,45 +561,6 @@ getAdjustedProbability(BranchProbability OrigProb, return SuccProb; } -/// Check if a block should be tail duplicated. -/// \p BB Block to check. -bool MachineBlockPlacement::shouldTailDuplicate(MachineBasicBlock *BB) { - // Blocks with single successors don't create additional fallthrough - // opportunities. Don't duplicate them. TODO: When conditional exits are - // analyzable, allow them to be duplicated. - bool IsSimple = TailDup.isSimpleBB(BB); - - if (BB->succ_size() == 1) - return false; - return TailDup.shouldTailDuplicate(IsSimple, *BB); -} - -/// When the option TailDupPlacement 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. In -/// addition we keep a set of blocks that have been tail-duplicated into and -/// allow those blocks to be unplaced as well. This allows the creation of a -/// second (larger) spine and a short fallthrough spine. -/// We also identify blocks with the CFG that would have been produced by -/// tail-duplication and lay them out in the same manner. -bool MachineBlockPlacement::canTailDuplicateUnplacedPreds( - MachineBasicBlock *BB, MachineBasicBlock *Succ, BlockChain &Chain, - const BlockFilterSet *BlockFilter) { - if (!shouldTailDuplicate(Succ)) - return false; - - for (MachineBasicBlock *Pred : Succ->predecessors()) { - // Make sure all unplaced and unfiltered predecessors can be - // tail-duplicated into. - if (Pred == BB || (BlockFilter && !BlockFilter->count(Pred)) - || BlockToChain[Pred] == &Chain) - continue; - if (!TailDup.canTailDuplicate(Succ, Pred)) - return false; - } - return true; -} - /// When the option OutlineOptionalBranches is on, this method /// checks if the fallthrough candidate block \p Succ (of block /// \p BB) also has other unscheduled predecessor blocks which @@ -677,12 +634,6 @@ bool MachineBlockPlacement::hasBetterLayoutPredecessor( if (SuccChain.UnscheduledPredecessors == 0) return false; - // As a heuristic, if we can duplicate the block into all its unscheduled - // predecessors, we return false. - if (TailDupPlacement - && canTailDuplicateUnplacedPreds(BB, Succ, Chain, BlockFilter)) - return false; - // There are two basic scenarios here: // ------------------------------------- // Case 1: triangular shape CFG (if-then): @@ -1957,8 +1908,13 @@ bool MachineBlockPlacement::maybeTailDuplicateBlock( DuplicatedToLPred = false; DEBUG(dbgs() << "Redoing tail duplication for Succ#" << BB->getNumber() << "\n"); - - if (!shouldTailDuplicate(BB)) + bool IsSimple = TailDup.isSimpleBB(BB); + // Blocks with single successors don't create additional fallthrough + // opportunities. Don't duplicate them. TODO: When conditional exits are + // analyzable, allow them to be duplicated. + if (!IsSimple && BB->succ_size() == 1) + return false; + if (!TailDup.shouldTailDuplicate(IsSimple, *BB)) return false; // This has to be a callback because none of it can be done after // BB is deleted. @@ -2011,7 +1967,6 @@ bool MachineBlockPlacement::maybeTailDuplicateBlock( llvm::function_ref<void(MachineBasicBlock*)>(RemovalCallback); SmallVector<MachineBasicBlock *, 8> DuplicatedPreds; - bool IsSimple = TailDup.isSimpleBB(BB); TailDup.tailDuplicateAndUpdate(IsSimple, BB, LPred, &DuplicatedPreds, &RemovalCallbackRef); |
