IR: Make stripDebugInfo robust against (invalid) empty basic blocks

Since stripDebugInfo runs before the verifier when reading IR, we can
end up in a situation where we read some invalid IR but don't know its
invalid yet. Before this patch we would crash in stripDebugInfo when
given IR with a completely empty basic block, and after we get a nice
error from the verifier instead.

llvm-svn: 311202

llvm/lib/IR/DebugInfo.cpp

@@ -311,6 +311,9 @@ bool llvm::stripDebugInfo(Function &F) {
     }
 
     auto *TermInst = BB.getTerminator();
+    if (!TermInst)
+      // This is invalid IR, but we may not have run the verifier yet
+      continue;
     if (auto *LoopID = TermInst->getMetadata(LLVMContext::MD_loop)) {
       auto *NewLoopID = LoopIDsMap.lookup(LoopID);
       if (!NewLoopID)