[turbofan]: Support using push instructions for setting up tail call parameters

src/compiler/gap-resolver.h

Index: src/compiler/gap-resolver.h
diff --git a/src/compiler/gap-resolver.h b/src/compiler/gap-resolver.h
index 19806f568a82faf27b5d6e60f12b195d1bed5208..7459b8964e5df898fd04bab84767df0d34dfb2fd 100644
--- a/src/compiler/gap-resolver.h
+++ b/src/compiler/gap-resolver.h
@@ -31,6 +31,22 @@ class GapResolver final {
   // Resolve a set of parallel moves, emitting assembler instructions.
   void Resolve(ParallelMove* parallel_move) const;
 
+  enum PushTypeFlag {
+    kImmediatePush = 0x1,
+    kScalarPush = 0x2,
+    kFloat32Push = 0x4,
+    kFloat64Push = 0x8,
+    kFloatPush = kFloat32Push | kFloat64Push
+  };
+
+  typedef base::Flags<PushTypeFlag> PushTypeFlags;
+
+  // Generate a list moves from an instruction that are candidates to be turned
+  // into push instructions on platforms that support them.
+  static void GetPushCompatibleMoves(Zone* zone, Instruction* instr,

[Mircea Trofin, 2016/06/30 15:32:34]

Is this just for tail calls cases, or in general?

Could you add a comment as to what specifically makes a move instruction a
candidate to be turned into a 
push?

[danno, 2016/07/01 07:31:57]

Eventually, I'd like to convert the "normal" call mechanism to use this too, but
there is more prep work to do this. Given how bad the code was for tail calls in
its current from, going this path sets the bar low, allowing some of the
infrastructure in place before switching everything over. I'll explain this in
the overall comment for the CL.

+                                     PushTypeFlags push_type,
+                                     ZoneVector<MoveOperands*>* pushes);
+
  private:
   // Perform the given move, possibly requiring other moves to satisfy
   // dependencies.