Disconnects code objects from infrequently used unoptimized functions.

runtime/vm/flow_graph_compiler_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM.
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
+#include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/deopt_instructions.h"
 #include "vm/il_printer.h"
 #include "vm/locations.h"
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/stack_frame.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
 
@@ skipping 1340 matching lines @@
   __ cmp(R4, ShifterOperand(R0));
   __ b(&update, NE);
 
   __ Bind(&call_target_function);
   // Call the target found in the cache.  For a class id match, this is a
   // proper target for the given name and arguments descriptor.  If the
   // illegal class id was found, the target is a cache miss handler that can
   // be invoked as a normal Dart function.
   __ add(IP, R2, ShifterOperand(R3, LSL, 2));
   __ ldr(R0, FieldAddress(IP, base + kWordSize));
-  __ ldr(R0, FieldAddress(R0, Function::code_offset()));
-  __ ldr(R0, FieldAddress(R0, Code::instructions_offset()));
+  __ ldr(R1, FieldAddress(R0, Function::code_offset()));
+  if (FLAG_collect_code) {
+    // If we are collecting code, the code object may be null.
+    Label is_compiled;
+    __ CompareImmediate(R1, reinterpret_cast<intptr_t>(Object::null()));
+    __ b(&is_compiled, NE);
+    __ EnterStubFrame();

[srdjan, 2013/10/23 15:58:13]

I am not sure that we can do EnterStubFrame in compiled code. Typically we call
to a stub which does EnterStubFrame. This means that there must be a PC of
compiled code on the stack before doing EnterStubFrame.

Also: megamorphic calls are emitted only in optimized code, i.e., you will never
hit this since code is not cleared if optimized code exists.

[zra, 2013/10/23 17:39:37]

Can the megamorphic call be a call to unoptimized code? Because I am getting a
null code pointer here.

Either way, I've updated to use GenerateCallRuntime. It seems no new frame is
needed here, following the example of other runtime calls from generated code.

[zra, 2013/10/23 23:27:52]

Moved call to a stub.

+    // Preserve arg desc. and IC data object.
+    __ PushList((1 << R4) | (1 << R5));
+    __ Push(R0);  // Pass function.
+    __ CallRuntime(kCompileFunctionRuntimeEntry, 1);
+    __ Pop(R0);  // Discard argument.
+    __ PopList((1 << R4) | (1 << R5));  // Restore arg desc. and IC data.
+    __ LeaveStubFrame();
+    // R0: target function.
+    __ ldr(R1, FieldAddress(R0, Function::code_offset()));
+    __ Bind(&is_compiled);
+  }
+  __ ldr(R0, FieldAddress(R1, Code::instructions_offset()));
   __ LoadObject(R5, ic_data);
   __ LoadObject(R4, arguments_descriptor);
   __ AddImmediate(R0, Instructions::HeaderSize() - kHeapObjectTag);
   __ blx(R0);
   AddCurrentDescriptor(PcDescriptors::kOther, Isolate::kNoDeoptId, token_pos);
   RecordSafepoint(locs);
   AddDeoptIndexAtCall(Isolate::ToDeoptAfter(deopt_id), token_pos);
   __ Drop(argument_count);
 }
 
@@ skipping 528 matching lines @@
   DRegister dreg = EvenDRegisterOf(reg);
   __ vldrd(dreg, Address(SP, kDoubleSize, Address::PostIndex));
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM