Detect simple tail calls

src/compiler/linkage.cc

Index: src/compiler/linkage.cc
diff --git a/src/compiler/linkage.cc b/src/compiler/linkage.cc
index 29d4388857fdf781f8b614c9f32a37adca859b19..f117f9f076d298bd16d51c48c89e7f7298b89ba3 100644
--- a/src/compiler/linkage.cc
+++ b/src/compiler/linkage.cc
@@ -34,7 +34,7 @@ std::ostream& operator<<(std::ostream& os, const CallDescriptor& d) {
   // TODO(svenpanne) Output properties etc. and be less cryptic.
   return os << d.kind() << ":" << d.debug_name() << ":r" << d.ReturnCount()
             << "j" << d.JSParameterCount() << "i" << d.InputCount() << "f"
-            << d.FrameStateCount();
+            << d.FrameStateCount() << "t" << d.IsTailCallAllowed();
 }
 
 
@@ -141,6 +141,17 @@ bool Linkage::NeedsFrameState(Runtime::FunctionId function) {
 }
 
 
+bool CallDescriptor::UsesOnlyRegisters() const {
+  for (size_t i = 0; i < InputCount(); ++i) {
+    if (!GetInputLocation(i).is_register()) return false;
+  }
+  for (size_t i = 0; i < ReturnCount(); ++i) {
+    if (!GetReturnLocation(i).is_register()) return false;
+  }
+  return true;
+}
+
+
 //==============================================================================
 // Provide unimplemented methods on unsupported architectures, to at least link.
 //==============================================================================