Detect simple tail calls

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

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/scopes.h"
@@ skipping 509 matching lines @@
     if (instr->InputAt(4)->IsRegister()) {                       \
       Register value = i.InputRegister(4);                       \
       ASSEMBLE_CHECKED_STORE_INTEGER_IMPL(asm_instr, Register);  \
     } else {                                                     \
       Immediate value = i.InputImmediate(4);                     \
       ASSEMBLE_CHECKED_STORE_INTEGER_IMPL(asm_instr, Immediate); \
     }                                                            \
   } while (false)
 
 
+void CodeGenerator::FixFrameForTailCall() {

[Benedikt Meurer, 2015/04/29 04:06:05]

Hm, FixFrameForTailCall is not an appropriate name. How about
AssembleDeconstructActivationRecord?

[Sven Panne, 2015/04/29 10:24:18]

Done.

+  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));

[Benedikt Meurer, 2015/04/29 04:06:05]

Had to close my eyes to review these lines of code...

[Sven Panne, 2015/04/29 10:24:18]

... and I had to close my eyes to write them. :-D That's the beauty of our
current calling conventions...

+    __ addq(rsp, Immediate(bytes_to_pop));
+  }
+}
+
+
 // Assembles an instruction after register allocation, producing machine code.
 void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
   X64OperandConverter i(this, instr);
 
   switch (ArchOpcodeField::decode(instr->opcode())) {
     case kArchCallCodeObject: {
       EnsureSpaceForLazyDeopt();
       if (HasImmediateInput(instr, 0)) {
         Handle<Code> code = Handle<Code>::cast(i.InputHeapObject(0));
         __ Call(code, RelocInfo::CODE_TARGET);
       } else {
         Register reg = i.InputRegister(0);
         int entry = Code::kHeaderSize - kHeapObjectTag;
         __ Call(Operand(reg, entry));
       }
       RecordCallPosition(instr);
       break;
     }
+    case kArchTailCallCodeObject: {
+      FixFrameForTailCall();
+      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);
       if (FLAG_debug_code) {
         // Check the function's context matches the context argument.
         __ cmpp(rsi, FieldOperand(func, JSFunction::kContextOffset));
         __ Assert(equal, kWrongFunctionContext);
       }
       __ Call(FieldOperand(func, JSFunction::kCodeEntryOffset));
       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);
+      }
+      FixFrameForTailCall();
+      __ jmp(FieldOperand(func, JSFunction::kCodeEntryOffset));
+      break;
+    }
     case kArchJmp:
       AssembleArchJump(i.InputRpo(0));
       break;
     case kArchLookupSwitch:
       AssembleArchLookupSwitch(instr);
       break;
     case kArchTableSwitch:
       AssembleArchTableSwitch(instr);
       break;
     case kArchNop:
@@ skipping 1095 matching lines @@
     }
   }
   MarkLazyDeoptSite();
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace compiler
 }  // namespace v8