[turbofan] Implement tail calls with differing stack parameter counts

src/compiler/linkage.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/code-stubs.h"
 #include "src/compiler.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/node.h"
 #include "src/compiler/pipeline.h"
@@ skipping 34 matching lines @@
 bool CallDescriptor::HasSameReturnLocationsAs(
     const CallDescriptor* other) const {
   if (ReturnCount() != other->ReturnCount()) return false;
   for (size_t i = 0; i < ReturnCount(); ++i) {
     if (GetReturnLocation(i) != other->GetReturnLocation(i)) return false;
   }
   return true;
 }
 
 
-bool CallDescriptor::CanTailCall(const Node* node) const {
+bool CallDescriptor::CanTailCall(const Node* node, size_t* stack_parameters_in,
+                                 size_t* preserved_stack_parameters_in,
+                                 size_t* stack_parameters_out,
+                                 size_t* register_parameters_out) const {
+  *stack_parameters_in = 0;
+  *stack_parameters_out = 0;
+  *preserved_stack_parameters_in = 0;
+  *register_parameters_out = 0;
+
   // Determine the number of stack parameters passed in
-  size_t stack_params = 0;
   for (size_t i = 0; i < InputCount(); ++i) {
     if (!GetInputLocation(i).is_register()) {
-      ++stack_params;
+      ++(*stack_parameters_in);
     }
   }
   // Ensure the input linkage contains the stack parameters in the right order
   size_t current_stack_param = 0;
   for (size_t i = 0; i < InputCount(); ++i) {
     if (!GetInputLocation(i).is_register()) {
       if (GetInputLocation(i) !=
           LinkageLocation(static_cast<int>(current_stack_param) -
-                          static_cast<int>(stack_params))) {
+                          static_cast<int>(*stack_parameters_in))) {
         return false;
       }
       ++current_stack_param;
     }
   }
   // Tail calling is currently allowed if return locations match and all
   // parameters are either in registers or on the stack but match exactly in
   // number and content.
   CallDescriptor const* other = OpParameter<CallDescriptor const*>(node);
   if (!HasSameReturnLocationsAs(other)) return false;
+
   size_t current_input = 0;
   size_t other_input = 0;
+  bool stack_param_match = true;
   while (true) {
     if (other_input >= other->InputCount()) {
-      while (current_input < InputCount()) {
-        if (!GetInputLocation(current_input).is_register()) {
-          return false;
-        }
-        ++current_input;
-      }
       return true;
     }
     if (current_input >= InputCount()) {
       while (other_input < other->InputCount()) {
         if (!other->GetInputLocation(other_input).is_register()) {
-          return false;
+          (*stack_parameters_out)++;
+        } else {
+          ++(*register_parameters_out);
         }
         ++other_input;
       }
+      // Allow adding stack parameters for the tail call
       return true;
     }
     if (GetInputLocation(current_input).is_register()) {
       ++current_input;
       continue;
     }
     if (other->GetInputLocation(other_input).is_register()) {
       ++other_input;
+      ++(*register_parameters_out);
       continue;
     }
-    if (GetInputLocation(current_input) !=
-        other->GetInputLocation(other_input)) {
-      return false;
-    }
     Node* input = node->InputAt(static_cast<int>(other_input));
     if (input->opcode() != IrOpcode::kParameter) {
-      return false;
+      stack_param_match = false;
+    } else {
+      // Make sure that the parameter input passed through to the tail call
+      // corresponds to the correct stack slot.
+      size_t param_index = ParameterIndexOf(input->op());
+      if (param_index != current_input - 1) {
+        stack_param_match = false;
+      }
     }
-    // Make sure that the parameter input passed through to the tail call
-    // corresponds to the correct stack slot.
-    size_t param_index = ParameterIndexOf(input->op());
-    if (param_index != current_input - 1) {
-      return false;
+    if (stack_param_match) {
+      (*preserved_stack_parameters_in)++;
     }
+    (*stack_parameters_out)++;
     ++current_input;
     ++other_input;
   }
   UNREACHABLE();
   return false;
 }
 
 
 CallDescriptor* Linkage::ComputeIncoming(Zone* zone, CompilationInfo* info) {
   if (info->code_stub() != NULL) {
@@ skipping 149 matching lines @@
 
 CallDescriptor* Linkage::GetSimplifiedCDescriptor(Zone* zone,
                                                   const MachineSignature* sig) {
   UNIMPLEMENTED();
   return NULL;
 }
 #endif  // !V8_TURBOFAN_BACKEND
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8