Detect simple tail calls

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index 9241d8355f7079691a01d1dc18e3994f93b2ae94..0f1e959adc7efd0cdacf20c38255032cdfa3cae0 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -527,6 +527,23 @@ class OutOfLineTruncateDoubleToI final : public OutOfLineCode {
   } while (false)
 
 
+void CodeGenerator::AssembleDeconstructActivationRecord() {
+  CallDescriptor* descriptor = linkage()->GetIncomingDescriptor();
+  int stack_slots = frame()->GetSpillSlotCount();
+  if (descriptor->IsJSFunctionCall() || stack_slots > 0) {
+    __ movq(rsp, rbp);
+    __ popq(rbp);
+    int32_t bytes_to_pop =
+        descriptor->IsJSFunctionCall()
+            ? static_cast<int32_t>(descriptor->JSParameterCount() *
+                                   kPointerSize)
+            : 0;
+    __ popq(Operand(rsp, bytes_to_pop));
+    __ addq(rsp, Immediate(bytes_to_pop));
+  }
+}
+
+
 // Assembles an instruction after register allocation, producing machine code.
 void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
   X64OperandConverter i(this, instr);
@@ -545,6 +562,18 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       RecordCallPosition(instr);
       break;
     }
+    case kArchTailCallCodeObject: {
+      AssembleDeconstructActivationRecord();
+      if (HasImmediateInput(instr, 0)) {
+        Handle<Code> code = Handle<Code>::cast(i.InputHeapObject(0));
+        __ jmp(code, RelocInfo::CODE_TARGET);
+      } else {
+        Register reg = i.InputRegister(0);
+        int entry = Code::kHeaderSize - kHeapObjectTag;
+        __ jmp(Operand(reg, entry));
+      }
+      break;
+    }
     case kArchCallJSFunction: {
       EnsureSpaceForLazyDeopt();
       Register func = i.InputRegister(0);
@@ -557,6 +586,17 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       RecordCallPosition(instr);
       break;
     }
+    case kArchTailCallJSFunction: {
+      Register func = i.InputRegister(0);
+      if (FLAG_debug_code) {
+        // Check the function's context matches the context argument.
+        __ cmpp(rsi, FieldOperand(func, JSFunction::kContextOffset));
+        __ Assert(equal, kWrongFunctionContext);
+      }
+      AssembleDeconstructActivationRecord();
+      __ jmp(FieldOperand(func, JSFunction::kCodeEntryOffset));
+      break;
+    }
     case kArchJmp:
       AssembleArchJump(i.InputRpo(0));
       break;