Tail call from TurboFan into select runtime calls

src/compiler/linkage-impl.h

Index: src/compiler/linkage-impl.h
diff --git a/src/compiler/linkage-impl.h b/src/compiler/linkage-impl.h
index 6641ef130982cc39de530c23d4243179ec6904d4..4694dd7dbd0baf514b195cf22cb5c2fb714b409c 100644
--- a/src/compiler/linkage-impl.h
+++ b/src/compiler/linkage-impl.h
@@ -7,6 +7,7 @@
 
 #include "src/code-stubs.h"
 #include "src/compiler/osr.h"
+#include "src/runtime/runtime.h"
 
 namespace v8 {
 namespace internal {
@@ -119,6 +120,9 @@ class LinkageHelper {
     CallDescriptor::Flags flags = Linkage::FrameStateInputCount(function_id) > 0
                                       ? CallDescriptor::kNeedsFrameState
                                       : CallDescriptor::kNoFlags;
+    if (Runtime::SupportsTailCall(function_id)) {

[Michael Starzinger, 2015/08/04 15:01:54]

This new predicate on {Runtime} is similar to Linkage::FrameStateInputCount. Can
we move it to {Linkage} into the linkage.cc file for consistency? I agree that
this decouples it from the list of runtime functions (which might be
controversial), but we already went with that for the frame states, and I would
rather keep it consistent. WDYT?

+      flags |= CallDescriptor::kSupportsTailCalls;
+    }
 
     // The target for runtime calls is a code object.
     MachineType target_type = kMachAnyTagged;