Merge r8237 to V8 3.2 branch. Fix bug v8:1434, optimized compare of undefined can fail.

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 8253)
+++ src/hydrogen.cc	(working copy)
@@ -1765,6 +1765,7 @@
   // change instructions for them.
   HInstruction* new_value = NULL;
   bool is_truncating = use->CheckFlag(HValue::kTruncatingToInt32);
+  bool deoptimize_on_undefined = use->CheckFlag(HValue::kDeoptimizeOnUndefined);
   if (value->IsConstant()) {
     HConstant* constant = HConstant::cast(value);
     // Try to create a new copy of the constant with the new representation.
@@ -1774,8 +1775,8 @@
   }
 
   if (new_value == NULL) {
-    new_value =
-        new(zone()) HChange(value, value->representation(), to, is_truncating);
+    new_value = new(zone()) HChange(value, value->representation(), to,
+                                    is_truncating, deoptimize_on_undefined);
   }
 
   new_value->InsertBefore(next);
@@ -1916,6 +1917,41 @@
 }
 
 
+void HGraph::RecursivelyMarkPhiDeoptimizeOnUndefined(HPhi* phi) {
+  if (phi->CheckFlag(HValue::kDeoptimizeOnUndefined)) return;
+  phi->SetFlag(HValue::kDeoptimizeOnUndefined);
+  for (int i = 0; i < phi->OperandCount(); ++i) {
+    HValue* input = phi->OperandAt(i);
+    if (input->IsPhi()) {
+      RecursivelyMarkPhiDeoptimizeOnUndefined(HPhi::cast(input));
+    }
+  }
+}
+
+
+void HGraph::MarkDeoptimizeOnUndefined() {
+  HPhase phase("MarkDeoptimizeOnUndefined", this);
+  // Compute DeoptimizeOnUndefined flag for phis.
+  // Any phi that can reach a use with DeoptimizeOnUndefined set must
+  // have DeoptimizeOnUndefined set.  Currently only HCompare, with
+  // double input representation, has this flag set.
+  // The flag is used by HChange tagged->double, which must deoptimize
+  // if one of its uses has this flag set.
+  for (int i = 0; i < phi_list()->length(); i++) {
+    HPhi* phi = phi_list()->at(i);
+    if (phi->representation().IsDouble()) {
+      for (int j = 0; j < phi->uses()->length(); j++) {
+        HValue* use = phi->uses()->at(j);
+        if (use->CheckFlag(HValue::kDeoptimizeOnUndefined)) {
+          RecursivelyMarkPhiDeoptimizeOnUndefined(phi);
+          break;
+        }
+      }
+    }
+  }
+}
+
+
 void HGraph::ComputeMinusZeroChecks() {
   BitVector visited(GetMaximumValueID());
   for (int i = 0; i < blocks_.length(); ++i) {
@@ -2234,6 +2270,7 @@
 
   graph()->InitializeInferredTypes();
   graph()->Canonicalize();
+  graph()->MarkDeoptimizeOnUndefined();
   graph()->InsertRepresentationChanges();
   graph()->ComputeMinusZeroChecks();