Author: Guozhi Wei Date: 2020-12-14T12:48:55-08:00 New Revision: d50d7c37a159802c89454a6c53c0ec2e7949d84a
URL: https://github.com/llvm/llvm-project/commit/d50d7c37a159802c89454a6c53c0ec2e7949d84a DIFF: https://github.com/llvm/llvm-project/commit/d50d7c37a159802c89454a6c53c0ec2e7949d84a.diff LOG: [MBP] Prevent rotating a chain contains entry block The entry block should always be the first BB in a function. So we should not rotate a chain contains the entry block. Differential Revision: https://reviews.llvm.org/D92882 Added: Modified: llvm/lib/CodeGen/MachineBlockPlacement.cpp Removed: ################################################################################ diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index bd4640822a63..42586cbe06e0 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -2306,6 +2306,10 @@ void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain, if (Bottom == ExitingBB) return; + // The entry block should always be the first BB in a function. + if (Top->isEntryBlock()) + return; + bool ViableTopFallthrough = hasViableTopFallthrough(Top, LoopBlockSet); // If the header has viable fallthrough, check whether the current loop @@ -2380,6 +2384,11 @@ void MachineBlockPlacement::rotateLoopWithProfile( BlockChain &LoopChain, const MachineLoop &L, const BlockFilterSet &LoopBlockSet) { auto RotationPos = LoopChain.end(); + MachineBasicBlock *ChainHeaderBB = *LoopChain.begin(); + + // The entry block should always be the first BB in a function. + if (ChainHeaderBB->isEntryBlock()) + return; BlockFrequency SmallestRotationCost = BlockFrequency::getMaxFrequency(); @@ -2398,7 +2407,6 @@ void MachineBlockPlacement::rotateLoopWithProfile( // chain head is not the loop header. As we only consider natural loops with // single header, this computation can be done only once. BlockFrequency HeaderFallThroughCost(0); - MachineBasicBlock *ChainHeaderBB = *LoopChain.begin(); for (auto *Pred : ChainHeaderBB->predecessors()) { BlockChain *PredChain = BlockToChain[Pred]; if (!LoopBlockSet.count(Pred) && _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
