Ensure deoptimizing frames have a valid pc marker before deferred materialization.

BUG=http://dartbug.com/26131
R=fschneider@google.com

Review URL: https://codereview.chromium.org/1847623002 .

runtime/vm/code_generator.cc

@@ -1793,6 +1793,17 @@ END_LEAF_RUNTIME_ENTRY
 // materialization phase.
 DEFINE_RUNTIME_ENTRY(DeoptimizeMaterialize, 0) {
 #if !defined(DART_PRECOMPILED_RUNTIME)
+#if defined(DEBUG)
+  {
+    // We may rendezvous for a safepoint at entry or GC from the allocations
+    // below. Check the stack is walkable.
+    StackFrameIterator frames_iterator(StackFrameIterator::kValidateFrames);
+    StackFrame* frame = frames_iterator.NextFrame();
+    while (frame != NULL) {
+      frame = frames_iterator.NextFrame();
+    }
+  }
+#endif
   DeoptContext* deopt_context = isolate->deopt_context();
   intptr_t deopt_arg_count = deopt_context->MaterializeDeferredObjects();
   isolate->set_deopt_context(NULL);

runtime/vm/deopt_instructions.cc

@@ -666,9 +666,14 @@ class DeoptPcMarkerInstr : public DeoptInstr {
       return;
     }
 
-    *dest_addr = reinterpret_cast<intptr_t>(Object::null());
-    deopt_context->DeferPcMarkerMaterialization(
-        object_table_index_, dest_addr);
+    // We don't always have the Code object for the frame's corresponding
+    // unoptimized code as it may have been collected. Use a stub as the pc
+    // marker until we can recreate that Code object during deferred
+    // materialization to maintain the invariant that Dart frames always have
+    // a pc marker.
+    *reinterpret_cast<RawObject**>(dest_addr) =
+        StubCode::FrameAwaitingMaterialization_entry()->code();
+    deopt_context->DeferPcMarkerMaterialization(object_table_index_, dest_addr);
   }
 
  private:

runtime/vm/stub_code.h

@@ -63,6 +63,7 @@ class SnapshotWriter;
   V(Subtype2TestCache)                                                         \
   V(Subtype3TestCache)                                                         \
   V(CallClosureNoSuchMethod)                                                   \
+  V(FrameAwaitingMaterialization)                                              \
 
 // Is it permitted for the stubs above to refer to Object::null(), which is
 // allocated in the VM isolate and shared across all isolates.

runtime/vm/stub_code_arm.cc

@@ -2179,6 +2179,11 @@ void StubCode::GenerateICLookupThroughCodeStub(Assembler* assembler) {
   __ Ret();
 }
 
+
+void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
+  __ bkpt(0);
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM

runtime/vm/stub_code_arm64.cc

@@ -2232,6 +2232,11 @@ void StubCode::GenerateICLookupThroughCodeStub(Assembler* assembler) {
   __ ret();
 }
 
+
+void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
+  __ brk(0);
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64

runtime/vm/stub_code_ia32.cc

@@ -2093,6 +2093,12 @@ void StubCode::GenerateICLookupThroughCodeStub(Assembler* assembler) {
   __ int3();
 }
 
+
+
+void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
+  __ int3();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32

runtime/vm/stub_code_mips.cc

@@ -2345,6 +2345,11 @@ void StubCode::GenerateICLookupThroughCodeStub(Assembler* assembler) {
   __ Ret();
 }
 
+
+void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
+  __ break_(0);
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS

runtime/vm/stub_code_x64.cc

@@ -2220,6 +2220,11 @@ void StubCode::GenerateICLookupThroughCodeStub(Assembler* assembler) {
   __ ret();
 }
 
+
+void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
+  __ int3();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64