Detect simple tail calls

src/compiler/instruction-selector.cc

 // Copyright 2014 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/instruction-selector.h"
 
 #include <limits>
 
 #include "src/base/adapters.h"
 #include "src/compiler/instruction-selector-impl.h"
@@ skipping 498 matching lines @@
 #endif
 
   Node* input = block->control_input();
   switch (block->control()) {
     case BasicBlock::kGoto:
       return VisitGoto(block->SuccessorAt(0));
     case BasicBlock::kCall: {
       DCHECK_EQ(IrOpcode::kCall, input->opcode());
       BasicBlock* success = block->SuccessorAt(0);
       BasicBlock* exception = block->SuccessorAt(1);
-      return VisitCall(input, exception), VisitGoto(success);
+      return VisitCall(input, exception, NORMAL_CALL), VisitGoto(success);
     }
     case BasicBlock::kBranch: {
       DCHECK_EQ(IrOpcode::kBranch, input->opcode());
       BasicBlock* tbranch = block->SuccessorAt(0);
       BasicBlock* fbranch = block->SuccessorAt(1);
       if (tbranch == fbranch) return VisitGoto(tbranch);
       // Treat special Branch(Always, IfTrue, IfFalse) as Goto(IfTrue).
       Node* const condition = input->InputAt(0);
       if (condition->opcode() == IrOpcode::kAlways) return VisitGoto(tbranch);
       return VisitBranch(input, tbranch, fbranch);
@@ skipping 22 matching lines @@
       DCHECK_LE(sw.min_value, sw.max_value);
       // Note that {value_range} can be 0 if {min_value} is -2^31 and
       // {max_value}
       // is 2^31-1, so don't assume that it's non-zero below.
       sw.value_range = 1u + bit_cast<uint32_t>(sw.max_value) -
                        bit_cast<uint32_t>(sw.min_value);
       return VisitSwitch(input, sw);
     }
     case BasicBlock::kReturn: {
       DCHECK_EQ(IrOpcode::kReturn, input->opcode());
-      return VisitReturn(input->InputAt(0));
+      return VisitReturn(input);
     }
     case BasicBlock::kDeoptimize: {
       // If the result itself is a return, return its input.
       Node* value =
           (input != nullptr && input->opcode() == IrOpcode::kDeoptimize)
               ? input->InputAt(0)
               : input;
       return VisitDeoptimize(value);
     }
     case BasicBlock::kThrow:
@@ skipping 56 matching lines @@
     case IrOpcode::kFloat64Constant:
       return MarkAsDouble(node), VisitConstant(node);
     case IrOpcode::kHeapConstant:
       return MarkAsReference(node), VisitConstant(node);
     case IrOpcode::kNumberConstant: {
       double value = OpParameter<double>(node);
       if (!IsSmiDouble(value)) MarkAsReference(node);
       return VisitConstant(node);
     }
     case IrOpcode::kCall:
-      return VisitCall(node, nullptr);
+      return VisitCall(node, nullptr, NORMAL_CALL);
     case IrOpcode::kFrameState:
     case IrOpcode::kStateValues:
       return;
     case IrOpcode::kLoad: {
       LoadRepresentation rep = OpParameter<LoadRepresentation>(node);
       MarkAsRepresentation(rep, node);
       return VisitLoad(node);
     }
     case IrOpcode::kStore:
       return VisitStore(node);
@@ skipping 384 matching lines @@
 }
 
 
 void InstructionSelector::VisitGoto(BasicBlock* target) {
   // jump to the next block.
   OperandGenerator g(this);
   Emit(kArchJmp, g.NoOutput(), g.Label(target));
 }
 
 
-void InstructionSelector::VisitReturn(Node* value) {
+// Returns the call node if the given return node is part of a tail call,
+// nullptr otherwise.
+static Node* DetectTailCall(Node* ret) {

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

Nit: Use anonymous namespace instead of static, and rename to something like
TryMatchTailCall.

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

Done.

+  // The value which is returned must be the result of a potential tail call,
+  // there must be no try/catch/finally around the call, and there must be no
+  // effects between the call and the return.
+  Node* call = NodeProperties::GetValueInput(ret, 0);
+  if (call->opcode() != IrOpcode::kCall ||
+      !OpParameter<const CallDescriptor*>(call)->IsTailCallAllowed() ||
+      NodeProperties::IsExceptionalCall(call) ||
+      NodeProperties::GetEffectInput(ret, 0) != call) {
+    return nullptr;
+  }
+  // Furthermore, control has to flow via an IfSuccess from the call (for calls
+  // which can throw), or the return and the call have to use the same control
+  // input (for calls which can't throw).
+  Node* control = NodeProperties::GetControlInput(ret, 0);
+  return ((control->opcode() == IrOpcode::kIfSuccess)
+              ? (NodeProperties::GetControlInput(control, 0) == call)

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

Urghs, can we please not nest tenary operators?

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

Booh! Functional programming FTW! ;-) Nevertheless: Done... :-/

+              : (control == NodeProperties::GetControlInput(call, 0)))
+             ? call
+             : nullptr;
+}
+
+
+void InstructionSelector::VisitReturn(Node* node) {
+  if (FLAG_turbo_tail_calls) {
+    Node* call = DetectTailCall(node);
+    if (call != nullptr &&
+        OpParameter<const CallDescriptor*>(call)->UsesOnlyRegisters()) {
+      return VisitCall(call, nullptr, TAIL_CALL);
+    }
+  }
+  Node* value = NodeProperties::GetValueInput(node, 0);
   DCHECK_NOT_NULL(value);
   OperandGenerator g(this);
   Emit(kArchRet, g.NoOutput(),
        g.UseLocation(value, linkage()->GetReturnLocation(),
                      linkage()->GetReturnType()));
 }
 
 
 void InstructionSelector::VisitDeoptimize(Node* value) {
   OperandGenerator g(this);
@@ skipping 137 matching lines @@
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {
   return MachineOperatorBuilder::Flag::kNoFlags;
 }
 
 #endif  // !V8_TURBOFAN_BACKEND
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8