Change heuristics for deciding phi-representation types to use int32 more frequently.

src/hydrogen.cc

Index: src/hydrogen.cc
===================================================================
--- src/hydrogen.cc	(revision 7737)
+++ src/hydrogen.cc	(working copy)
@@ -1575,14 +1575,13 @@
   }
 
   if (non_tagged_count >= tagged_count) {
-    // More untagged than tagged.
-    if (double_count > 0) {
-      // There is at least one usage that is a double => guess that the
-      // correct representation is double.
-      return Representation::Double();
+    if (int32_count > 0 && value->IsPhi()) {

[Kevin Millikin (Chromium), 2011/05/03 07:58:32]

if (int32_count > 0) {
  if (!value->IsPhi() || value->IsConvertibleToInteger()) {
    return Representation::Integer32();
  }
}
if (double_count > 0) ...
    

+      HPhi* phi = HPhi::cast(value);
+      if (phi->IsConvertibleToInteger()) return Representation::Integer32();
     } else if (int32_count > 0) {
       return Representation::Integer32();
     }
+    if (double_count > 0) return Representation::Double();
   }
   return Representation::None();
 }
@@ -1595,7 +1594,7 @@
   // bit-vector of length <number of phis>.
   const ZoneList<HPhi*>* phi_list = graph_->phi_list();
   int phi_count = phi_list->length();
-  ScopedVector<BitVector*> connected_phis(phi_count);
+  ZoneList<BitVector*> connected_phis(phi_count);
   for (int i = 0; i < phi_count; ++i) {
     phi_list->at(i)->InitRealUses(i);
     connected_phis[i] = new(zone()) BitVector(phi_count);
@@ -1636,6 +1635,25 @@
     }
   }
 
+  // (4) Compute phis that definitely can't be converted to integer
+  // without deoptimization and mark them to avoid unnecessary deoptimization.
+  change = true;
+  while (change) {
+    change = false;
+    for (int i = 0; i < phi_count; i++) {

[Kevin Millikin (Chromium), 2011/05/03 07:58:32]

All the other loops in this function use new-school ++i :)

+      HPhi* phi = phi_list->at(i);
+      for (int i = 0; i < phi->OperandCount(); i++) {

[Kevin Millikin (Chromium), 2011/05/03 07:58:32]

Please don't shadow the outer loop index even if you don't need it in the inner
loop!

+        if (phi->IsConvertibleToInteger() &&
+            !phi->OperandAt(i)->IsConvertibleToInteger()) {
+          phi->set_is_convertible_to_integer(false);
+          change = true;
+          break;
+        }
+      }
+    }
+  }
+
+
   for (int i = 0; i < graph_->blocks()->length(); ++i) {
     HBasicBlock* block = graph_->blocks()->at(i);
     const ZoneList<HPhi*>* phis = block->phis();