Give uses within a loop a greater weight when doing representation inference.

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
===================================================================
--- src/hydrogen-instructions.cc	(revision 9619)
+++ src/hydrogen-instructions.cc	(working copy)
@@ -67,6 +67,19 @@
 }
 
 
+template<class T> inline const T& min(const T& a, const T& b) {
+  return (a < b) ? a : b;
+}
+
+
+int HValue::LoopWeight() const {
+  const int w = FLAG_loop_weight;
+  static const int weights[] = { 1, w, w*w, w*w*w, w*w*w*w };

[fschneider, 2012/01/27 22:33:24]

I think no need for static here. Actually, I'd also be fine with hard-coding the
weight to 10 here, so that the compiler can inline the constants. Once set, we
probably don't need to change it often.

[Sven Panne, 2012/01/30 07:51:04]

Well, initializing the array every time wouldn't be very cool, either, so I went
for a 'static' (What I really wanted to write is 'iterate (*w) 1' ;-).  But
you're right, when we figured out a sensible weight, we should probably change
this to a simple switch on block()->LoopNestingDepth() and use a real constant.

+  return weights[min(block()->LoopNestingDepth(),
+                     static_cast<int>(ARRAY_SIZE(weights)-1))];
+}
+
+
 void HValue::AssumeRepresentation(Representation r) {
   if (CheckFlag(kFlexibleRepresentation)) {
     ChangeRepresentation(r);
@@ -1117,7 +1130,7 @@
     HValue* value = it.value();
     if (!value->IsPhi()) {
       Representation rep = value->RequiredInputRepresentation(it.index());
-      ++non_phi_uses_[rep.kind()];
+      non_phi_uses_[rep.kind()] += value->LoopWeight();
     }
   }
 }