From 66189212bbb0351ae98bbda70bd2cd819e86fd17 Mon Sep 17 00:00:00 2001 From: Roman Lebedev Date: Fri, 8 Jan 2021 00:51:29 +0300 Subject: [PATCH] [SimplifyCFG] MergeBlockIntoPredecessor(): switch to non-permissive DomTree updates ... which requires not deleting edges that were just deleted already, by not processing the same successor more than once. --- llvm/lib/Transforms/Utils/BasicBlockUtils.cpp | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp index 09888db..4d99067 100644 --- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp +++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp @@ -230,19 +230,21 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU, // These dominator edges will be redirected from Pred. std::vector Updates; if (DTU) { - Updates.reserve(1 + (2 * succ_size(BB))); + SmallSetVector UniqueSuccessors(succ_begin(BB), + succ_end(BB)); + Updates.reserve(1 + (2 * UniqueSuccessors.size())); // Add insert edges first. Experimentally, for the particular case of two // blocks that can be merged, with a single successor and single predecessor // respectively, it is beneficial to have all insert updates first. Deleting // edges first may lead to unreachable blocks, followed by inserting edges // making the blocks reachable again. Such DT updates lead to high compile // times. We add inserts before deletes here to reduce compile time. - for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) + for (BasicBlock *UniqueSuccessor : UniqueSuccessors) // This successor of BB may already have PredBB as a predecessor. - if (!llvm::is_contained(successors(PredBB), *I)) - Updates.push_back({DominatorTree::Insert, PredBB, *I}); - for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) - Updates.push_back({DominatorTree::Delete, BB, *I}); + if (!llvm::is_contained(successors(PredBB), UniqueSuccessor)) + Updates.push_back({DominatorTree::Insert, PredBB, UniqueSuccessor}); + for (BasicBlock *UniqueSuccessor : UniqueSuccessors) + Updates.push_back({DominatorTree::Delete, BB, UniqueSuccessor}); Updates.push_back({DominatorTree::Delete, PredBB, BB}); } @@ -303,7 +305,7 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU, isa(BB->getTerminator()) && "The successor list of BB isn't empty before " "applying corresponding DTU updates."); - DTU->applyUpdatesPermissive(Updates); + DTU->applyUpdates(Updates); DTU->deleteBB(BB); } else { BB->eraseFromParent(); // Nuke BB if DTU is nullptr. -- 2.7.4