Age code to allow reclaiming old unexecuted functions

src/x64/assembler-x64-inl.h

Index: src/x64/assembler-x64-inl.h
diff --git a/src/x64/assembler-x64-inl.h b/src/x64/assembler-x64-inl.h
index d022340c10a636ac66b2816690c4d24dc718512e..63ba58bcb18a3d4cb9d13dd3e728886321dddf2e 100644
--- a/src/x64/assembler-x64-inl.h
+++ b/src/x64/assembler-x64-inl.h
@@ -42,6 +42,9 @@ namespace internal {
 // Implementation of Assembler
 
 
+static const byte kCallOpcode = 0xE8;
+
+
 void Assembler::emitl(uint32_t x) {
   Memory::uint32_at(pc_) = x;
   pc_ += sizeof(uint32_t);
@@ -217,6 +220,12 @@ void RelocInfo::apply(intptr_t delta) {
   } else if (IsCodeTarget(rmode_)) {
     Memory::int32_at(pc_) -= static_cast<int32_t>(delta);
     CPU::FlushICache(pc_, sizeof(int32_t));
+  } else if (rmode_ == CODE_AGE_SEQUENCE) {
+    if (*pc_ == kCallOpcode) {
+      int32_t* p = reinterpret_cast<int32_t*>(pc_ + 1);
+      *p -= delta;  // Relocate entry.
+      CPU::FlushICache(p, sizeof(uint32_t));
+    }
   }
 }
 
@@ -355,6 +364,21 @@ bool RelocInfo::IsPatchedDebugBreakSlotSequence() {
 }
 
 
+Code* RelocInfo::code_age_stub() {
+  ASSERT(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
+  ASSERT(*pc_ == kCallOpcode);
+  return Code::GetCodeFromTargetAddress(
+      Assembler::target_address_at(pc_ + 1));
+}
+
+
+void RelocInfo::set_code_age_stub(Code* stub) {
+  ASSERT(*pc_ == kCallOpcode);
+  ASSERT(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
+  Assembler::set_target_address_at(pc_ + 1, stub->instruction_start());
+}
+
+
 Address RelocInfo::call_address() {
   ASSERT((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
          (IsDebugBreakSlot(rmode()) && IsPatchedDebugBreakSlotSequence()));
@@ -408,6 +432,8 @@ void RelocInfo::Visit(ObjectVisitor* visitor) {
   } else if (mode == RelocInfo::EXTERNAL_REFERENCE) {
     visitor->VisitExternalReference(this);
     CPU::FlushICache(pc_, sizeof(Address));
+  } else if (RelocInfo::IsCodeAgeSequence(mode)) {
+    visitor->VisitCodeAgeSequence(this);
 #ifdef ENABLE_DEBUGGER_SUPPORT
   // TODO(isolates): Get a cached isolate below.
   } else if (((RelocInfo::IsJSReturn(mode) &&
@@ -436,6 +462,8 @@ void RelocInfo::Visit(Heap* heap) {
   } else if (mode == RelocInfo::EXTERNAL_REFERENCE) {
     StaticVisitor::VisitExternalReference(this);
     CPU::FlushICache(pc_, sizeof(Address));
+  } else if (RelocInfo::IsCodeAgeSequence(mode)) {
+    StaticVisitor::VisitCodeAgeSequence(heap, this);
 #ifdef ENABLE_DEBUGGER_SUPPORT
   } else if (heap->isolate()->debug()->has_break_points() &&
              ((RelocInfo::IsJSReturn(mode) &&