Reapply "Initial implementation of on-stack replacement (OSR)."

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index 0ffb7f069370614b490e2ca9945c816bac7f8fa9..7366821de3841e7c18876a65f21d28b81c46b331 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -691,8 +691,14 @@ CompileType ParameterInstr::ComputeType() const {
   // However there are parameters that are known to match their declared type:
   // for example receiver and construction phase.
   GraphEntryInstr* graph_entry = block_->AsGraphEntry();
-  // Parameters at catch-blocks have type dynamic.
-  if (graph_entry == NULL) return CompileType::Dynamic();
+  // Parameters at catch blocks and OSR entries have type dynamic.
+  //
+  // TODO(kmillikin): Use the actual type of the parameter at OSR entry.
+  // The code below is not safe for OSR because it doesn't necessarily use
+  // the correct scope.
+  if ((graph_entry == NULL) || graph_entry->IsCompiledForOsr()) {
+    return CompileType::Dynamic();
+  }
 
   const Function& function = graph_entry->parsed_function().function();
   LocalScope* scope = graph_entry->parsed_function().node_sequence()->scope();