VM: [Kernel] Implement CatchBlockEntryInstr::should_restore_closure_context on all platforms.

runtime/vm/flow_graph_compiler_dbc.cc

Index: runtime/vm/flow_graph_compiler_dbc.cc
diff --git a/runtime/vm/flow_graph_compiler_dbc.cc b/runtime/vm/flow_graph_compiler_dbc.cc
index 4450561dddf7cbe65856ed954d4ae8cd8119d24a..5e0f8bce871702bc31336f5531f12c7461e89934 100644
--- a/runtime/vm/flow_graph_compiler_dbc.cc
+++ b/runtime/vm/flow_graph_compiler_dbc.cc
@@ -400,17 +400,23 @@ void FlowGraphCompiler::EmitFrameEntry() {
   }
 
   if (function.IsClosureFunction()) {
-    Register reg =
+    // In optimized mode the register allocator expects CurrentContext in the
+    // flow_graph_.num_copied_params() register at function entry.
+    // (see FlowGraphAllocator::ProcessInitialDefinition)
+    Register context_reg =
         is_optimizing() ? flow_graph_.num_copied_params() : context_index;
-    Register closure_reg = reg;
     LocalScope* scope = parsed_function().node_sequence()->scope();
     LocalVariable* local = scope->VariableAt(0);
+
+    Register closure_reg;
     if (local->index() > 0) {
-      __ Move(reg, -local->index());
+      __ Move(context_reg, -local->index());
+      closure_reg = context_reg;
     } else {
       closure_reg = -local->index() - 1;
     }
-    __ LoadField(reg, closure_reg, Closure::context_offset() / kWordSize);
+    __ LoadField(context_reg, closure_reg,
+                 Closure::context_offset() / kWordSize);
   } else if (has_optional_params && !is_optimizing()) {
     __ LoadConstant(context_index, Object::empty_context());
   }
@@ -440,6 +446,14 @@ uint16_t FlowGraphCompiler::ToEmbeddableCid(intptr_t cid,
 }
 
 
+intptr_t FlowGraphCompiler::CatchEntryRegForVariable(const LocalVariable& var) {
+  ASSERT(is_optimizing());
+  ASSERT(var.index() <= 0);
+  return kNumberOfCpuRegisters -
+         (flow_graph().num_non_copied_params() - var.index());
+}
+
+
 #undef __
 #define __ compiler_->assembler()->