[es6] Further fixing of tail Calls.

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 2ccd288048ebce1e15d48a86fb1cf4ace4e3aebf..057af184b279ae826f61b341d0441f966e7fdee2 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -389,6 +389,30 @@ void FullCodeGenerator::EmitBackEdgeBookkeeping(IterationStatement* stmt,
   PrepareForBailoutForId(stmt->OsrEntryId(), NO_REGISTERS);
 }
 
+void FullCodeGenerator::EmitProfilingCounterHandlingForReturnSequence(
+    bool is_tail_call) {
+  // Pretend that the exit is a backwards jump to the entry.
+  int weight = 1;
+  if (info_->ShouldSelfOptimize()) {
+    weight = FLAG_interrupt_budget / FLAG_self_opt_count;
+  } else {
+    int distance = masm_->pc_offset();
+    weight = Min(kMaxBackEdgeWeight, Max(1, distance / kCodeSizeMultiplier));
+  }
+  EmitProfilingCounterDecrement(weight);
+  Label ok;
+  __ j(positive, &ok, Label::kNear);
+  // Don't need to save result register if we are going to do a tail call.
+  if (!is_tail_call) {
+    __ Push(rax);
+  }
+  __ call(isolate()->builtins()->InterruptCheck(), RelocInfo::CODE_TARGET);
+  if (!is_tail_call) {
+    __ Pop(rax);
+  }
+  EmitProfilingCounterReset();
+  __ bind(&ok);
+}
 
 void FullCodeGenerator::EmitReturnSequence() {
   Comment cmnt(masm_, "[ Return sequence");
@@ -400,24 +424,7 @@ void FullCodeGenerator::EmitReturnSequence() {
       __ Push(rax);
       __ CallRuntime(Runtime::kTraceExit);
     }
-    // Pretend that the exit is a backwards jump to the entry.
-    int weight = 1;
-    if (info_->ShouldSelfOptimize()) {
-      weight = FLAG_interrupt_budget / FLAG_self_opt_count;
-    } else {
-      int distance = masm_->pc_offset();
-      weight = Min(kMaxBackEdgeWeight,
-                   Max(1, distance / kCodeSizeMultiplier));
-    }
-    EmitProfilingCounterDecrement(weight);
-    Label ok;
-    __ j(positive, &ok, Label::kNear);
-    __ Push(rax);
-    __ call(isolate()->builtins()->InterruptCheck(),
-            RelocInfo::CODE_TARGET);
-    __ Pop(rax);
-    EmitProfilingCounterReset();
-    __ bind(&ok);
+    EmitProfilingCounterHandlingForReturnSequence(false);
 
     SetReturnPosition(literal());
     __ leave();
@@ -2626,6 +2633,14 @@ void FullCodeGenerator::EmitCall(Call* expr, ConvertReceiverMode mode) {
 
   PrepareForBailoutForId(expr->CallId(), NO_REGISTERS);
   SetCallPosition(expr);
+  if (expr->tail_call_mode() == TailCallMode::kAllow) {
+    if (FLAG_trace) {
+      __ CallRuntime(Runtime::kTraceTailCall);
+    }
+    // Update profiling counters before the tail call since we will
+    // not return to this function.
+    EmitProfilingCounterHandlingForReturnSequence(true);
+  }
   Handle<Code> ic =
       CodeFactory::CallIC(isolate(), arg_count, mode, expr->tail_call_mode())
           .code();