From 55a68a24003a08f37e0d4704c8d89cd2c3f9f095 Mon Sep 17 00:00:00 2001 From: Wei Mi Date: Fri, 26 Jul 2019 20:59:22 +0000 Subject: [JumpThreading] Stop searching predecessor when the current bb is in a unreachable loop. updatePredecessorProfileMetadata in jumpthreading tries to find the first dominating predecessor block for a PHI value by searching upwards the predecessor block chain. But jumpthreading may see some temporary IR state which contains unreachable bb not being cleaned up. If an unreachable loop happens to be on the predecessor block chain, keeping chasing the predecessor block will run into an infinite loop. The patch fixes it. Differential Revision: https://reviews.llvm.org/D65310 llvm-svn: 367154 --- llvm/lib/Transforms/Scalar/JumpThreading.cpp | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'llvm/lib') diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp index b86bf2fefbe..459be213bd7 100644 --- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp +++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp @@ -224,13 +224,21 @@ static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) { BasicBlock *PhiBB) -> std::pair { auto *PredBB = IncomingBB; auto *SuccBB = PhiBB; + SmallPtrSet Visited; while (true) { BranchInst *PredBr = dyn_cast(PredBB->getTerminator()); if (PredBr && PredBr->isConditional()) return {PredBB, SuccBB}; + Visited.insert(PredBB); auto *SinglePredBB = PredBB->getSinglePredecessor(); if (!SinglePredBB) return {nullptr, nullptr}; + + // Stop searching when SinglePredBB has been visited. It means we see + // an unreachable loop. + if (Visited.count(SinglePredBB)) + return {nullptr, nullptr}; + SuccBB = PredBB; PredBB = SinglePredBB; } @@ -253,7 +261,9 @@ static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) { return; BasicBlock *PredBB = PredOutEdge.first; - BranchInst *PredBr = cast(PredBB->getTerminator()); + BranchInst *PredBr = dyn_cast(PredBB->getTerminator()); + if (!PredBr) + return; uint64_t PredTrueWeight, PredFalseWeight; // FIXME: We currently only set the profile data when it is missing. -- cgit v1.2.3