Track JS allocations as they arrive with no affection on performance when tracking is switched off

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 8f27374af5f156b9c6e85ef2f6622f4fd0821ec2..cc44f19383af2388741d325f3b9b465f0dbb3879 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -4941,9 +4941,19 @@ void SubStringStub::Generate(MacroAssembler* masm) {
     STATIC_ASSERT((kStringEncodingMask & kOneByteStringTag) != 0);
     STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
     __ testb(rbx, Immediate(kStringEncodingMask));
-    __ j(zero, &two_byte_slice, Label::kNear);
+    if (masm->isolate()->heap_profiler()->is_tracking_allocations()) {
+      // Make a long jump due to RecordObjectAllocation inside

[yurys, 2013/09/25 10:41:12]

You could calculate

Label::Distance distance =
masm->isolate()->heap_profiler()->is_tracking_allocations() ? Label::kFar :
Label::kNear;

once and use it in the two jumps below.

[Alexandra Mikhaylova, 2013/09/25 14:33:40]

Done.

+      // MacroAssembler::Allocate
+      __ j(zero, &two_byte_slice);
+    } else {
+      __ j(zero, &two_byte_slice, Label::kNear);
+    }
     __ AllocateAsciiSlicedString(rax, rbx, r14, &runtime);
-    __ jmp(&set_slice_header, Label::kNear);
+    if (masm->isolate()->heap_profiler()->is_tracking_allocations()) {
+      __ jmp(&set_slice_header);
+    } else {
+      __ jmp(&set_slice_header, Label::kNear);
+    }
     __ bind(&two_byte_slice);
     __ AllocateTwoByteSlicedString(rax, rbx, r14, &runtime);
     __ bind(&set_slice_header);