Refactored HInferRepresenation::TryChange a bit, making the heuristics a bit clearer.

Removed an unneeded check for phis: There are never HValues in the work list
which are not convertible to integer and are not a phi. (But even if they were,
ignoring IsConvertibleToInteger() then looks like the wrong thing to do.)
Review URL: http://codereview.chromium.org/7857033

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9225 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 070a927..a453651 100644 (file)
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -1649,18 +1649,20 @@ Representation HInferRepresentation::TryChange(HValue* value) {
   int non_tagged_count = double_count + int32_count;
 
   // If a non-loop phi has tagged uses, don't convert it to untagged.
-  if (value->IsPhi() && !value->block()->IsLoopHeader()) {
-    if (tagged_count > 0) return Representation::None();
+  if (value->IsPhi() && !value->block()->IsLoopHeader() && tagged_count > 0) {
+    return Representation::None();
   }
 
-  if (non_tagged_count >= tagged_count) {
-    if (int32_count > 0) {
-      if (!value->IsPhi() || value->IsConvertibleToInteger()) {
-        return Representation::Integer32();
-      }
-    }
-    if (double_count > 0) return Representation::Double();
+  // Prefer unboxing over boxing, the latter is more expensive.
+  if (tagged_count > non_tagged_count) Representation::None();
+
+  // Prefer Integer32 over Double, if possible.
+  if (int32_count > 0 && value->IsConvertibleToInteger()) {
+    return Representation::Integer32();
   }
+
+  if (double_count > 0) return Representation::Double();
+
   return Representation::None();
 }