IR: Fix BasicBlock::phis for empty blocks

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321567 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 8 insertions, 1 deletions

diff --git a/lib/IR/BasicBlock.cpp b/lib/IR/BasicBlock.cpp
index 22513924a96..938c40182b9 100644
--- a/lib/IR/BasicBlock.cpp
+++ b/lib/IR/BasicBlock.cpp
@@ -264,7 +264,8 @@ const BasicBlock *BasicBlock::getUniqueSuccessor() const {
 }
 
 iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
-  return make_range<phi_iterator>(dyn_cast<PHINode>(&front()), nullptr);
+  PHINode *P = empty() ? nullptr : dyn_cast<PHINode>(&*begin());
+  return make_range<phi_iterator>(P, nullptr);
 }
 
 /// This method is used to notify a BasicBlock that the
diff --git a/unittests/IR/BasicBlockTest.cpp b/unittests/IR/BasicBlockTest.cpp
index f1777e35b82..08a41ff3693 100644
--- a/unittests/IR/BasicBlockTest.cpp
+++ b/unittests/IR/BasicBlockTest.cpp
@@ -33,6 +33,12 @@ TEST(BasicBlockTest, PhiRange) {
   std::unique_ptr<BasicBlock> BB2(BasicBlock::Create(Context));
   BranchInst::Create(BB.get(), BB2.get());
 
+  // Make sure this doesn't crash if there are no phis.
+  for (auto &PN : BB->phis()) {
+    (void)PN;
+    EXPECT_TRUE(false) << "empty block should have no phis";
+  }
+
   // Make it a cycle.
   auto *BI = BranchInst::Create(BB.get(), BB.get());