VM: Improve receiver class check in polymorphic inlining.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 33059)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -84,10 +84,17 @@
 }
 
 
+static int LowestFirst(const intptr_t* a, const intptr_t* b) {
+  return *a - *b;
+}
+
+
 CheckClassInstr::CheckClassInstr(Value* value,
                                  intptr_t deopt_id,
                                  const ICData& unary_checks)
-    : unary_checks_(unary_checks), licm_hoisted_(false) {
+    : unary_checks_(unary_checks),
+      cids_(unary_checks.NumberOfChecks()),
+      licm_hoisted_(false) {
   ASSERT(unary_checks.IsZoneHandle());
   // Expected useful check data.
   ASSERT(!unary_checks_.IsNull());
@@ -98,6 +105,10 @@
   // Otherwise use CheckSmiInstr.
   ASSERT((unary_checks_.NumberOfChecks() != 1) ||
          (unary_checks_.GetReceiverClassIdAt(0) != kSmiCid));
+  for (intptr_t i = 0; i < unary_checks.NumberOfChecks(); ++i) {
+    cids_.Add(unary_checks.GetReceiverClassIdAt(i));
+  }
+  cids_.Sort(LowestFirst);
 }
 
 
@@ -140,6 +151,13 @@
 }
 
 
+bool CheckClassInstr::IsDenseSwitch() const {
+  return unary_checks().GetReceiverClassIdAt(0) != kSmiCid
+      && cids_.length() > 2
+      && cids_[cids_.length() - 1] - cids_[0] < kBitsPerWord;
+}
+
+
 bool LoadFieldInstr::IsUnboxedLoad() const {
   return FLAG_unbox_numeric_fields
       && (field() != NULL)