Detect simple tail calls

src/compiler/linkage.h

 // 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.
 
 #ifndef V8_COMPILER_LINKAGE_H_
 #define V8_COMPILER_LINKAGE_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/frame.h"
 #include "src/compiler/machine-type.h"
 #include "src/compiler/operator.h"
 #include "src/frames.h"
 #include "src/runtime/runtime.h"
 #include "src/zone.h"
 
 namespace v8 {
 namespace internal {
 
 class CallInterfaceDescriptor;
 
 namespace compiler {
 
 class OsrHelper;
 
 // Describes the location for a parameter or a return value to a call.
 class LinkageLocation {
  public:
   explicit LinkageLocation(int location) : location_(location) {}
 
+  bool is_register() const {
+    return 0 <= location_ && location_ <= ANY_REGISTER;
+  }
+
   static const int16_t ANY_REGISTER = 1023;
   static const int16_t MAX_STACK_SLOT = 32767;
 
   static LinkageLocation AnyRegister() { return LinkageLocation(ANY_REGISTER); }
 
+  bool operator==(const LinkageLocation& other) const {
+    return location_ == other.location_;
+  }
+
+  bool operator!=(const LinkageLocation& other) const {
+    return !(*this == other);
+  }
+
  private:
   friend class CallDescriptor;
   friend class OperandGenerator;
   //         location < 0     -> a stack slot on the caller frame
   // 0    <= location < 1023  -> a specific machine register
   // 1023 <= location < 1024  -> any machine register
   // 1024 <= location         -> a stack slot in the callee frame
   int16_t location_;
 };
 
 typedef Signature<LinkageLocation> LocationSignature;
 
 // Describes a call to various parts of the compiler. Every call has the notion
 // of a "target", which is the first input to the call.
 class CallDescriptor final : public ZoneObject {
  public:
   // Describes the kind of this call, which determines the target.
   enum Kind {
     kCallCodeObject,  // target is a Code object
     kCallJSFunction,  // target is a JSFunction object
     kCallAddress      // target is a machine pointer
   };
 
   enum Flag {
     kNoFlags = 0u,
     kNeedsFrameState = 1u << 0,
     kPatchableCallSite = 1u << 1,
     kNeedsNopAfterCall = 1u << 2,
     kHasExceptionHandler = 1u << 3,
+    kSupportsTailCalls = 1u << 4,
     kPatchableCallSiteWithNop = kPatchableCallSite | kNeedsNopAfterCall
   };
   typedef base::Flags<Flag> Flags;
 
   CallDescriptor(Kind kind, MachineType target_type, LinkageLocation target_loc,
                  const MachineSignature* machine_sig,
                  LocationSignature* location_sig, size_t js_param_count,
                  Operator::Properties properties,
                  RegList callee_saved_registers, Flags flags,
                  const char* debug_name = "")
@@ skipping 27 matching lines @@
   // The total number of inputs to this call, which includes the target,
   // receiver, context, etc.
   // TODO(titzer): this should input the framestate input too.
   size_t InputCount() const { return 1 + machine_sig_->parameter_count(); }
 
   size_t FrameStateCount() const { return NeedsFrameState() ? 1 : 0; }
 
   Flags flags() const { return flags_; }
 
   bool NeedsFrameState() const { return flags() & kNeedsFrameState; }
+  bool SupportsTailCalls() const { return flags() & kSupportsTailCalls; }
 
   LinkageLocation GetReturnLocation(size_t index) const {
     return location_sig_->GetReturn(index);
   }
 
   LinkageLocation GetInputLocation(size_t index) const {
     if (index == 0) return target_loc_;
     return location_sig_->GetParam(index - 1);
   }
 
   const MachineSignature* GetMachineSignature() const { return machine_sig_; }
 
   MachineType GetReturnType(size_t index) const {
     return machine_sig_->GetReturn(index);
   }
 
   MachineType GetInputType(size_t index) const {
     if (index == 0) return target_type_;
     return machine_sig_->GetParam(index - 1);
   }
 
   // Operator properties describe how this call can be optimized, if at all.
   Operator::Properties properties() const { return properties_; }
 
   // Get the callee-saved registers, if any, across this call.
   RegList CalleeSavedRegisters() const { return callee_saved_registers_; }
 
   const char* debug_name() const { return debug_name_; }
 
+  bool UsesOnlyRegisters() const;
+
+  bool HasSameReturnLocationsAs(const CallDescriptor* other) const;
+
  private:
   friend class Linkage;
 
   const Kind kind_;
   const MachineType target_type_;
   const LinkageLocation target_loc_;
   const MachineSignature* const machine_sig_;
   const LocationSignature* const location_sig_;
   const size_t js_param_count_;
   const Operator::Properties properties_;
@@ skipping 88 matching lines @@
   CallDescriptor* const incoming_;
 
   DISALLOW_COPY_AND_ASSIGN(Linkage);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LINKAGE_H_