Remove prototype checks for leaf maps in optimized code.

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
diff --git a/src/ia32/lithium-codegen-ia32.cc b/src/ia32/lithium-codegen-ia32.cc
index dfced7c221335f060f7c333e02c0ec38bb7516d8..36168130b29b020a1f977c8e11c8965c6f838d8e 100644
--- a/src/ia32/lithium-codegen-ia32.cc
+++ b/src/ia32/lithium-codegen-ia32.cc
@@ -100,6 +100,10 @@ void LCodeGen::FinishCode(Handle<Code> code) {
   if (!info()->IsStub()) {
     Deoptimizer::EnsureRelocSpaceForLazyDeoptimization(code);
   }
+  for (int i = 0 ; i < prototype_maps_.length(); i++) {
+    prototype_maps_.at(i)->AddDependentCode(
+        DependentCodes::kPrototypeCheckGroup, code);
+  }
 }
 
 
@@ -5332,9 +5336,16 @@ void LCodeGen::DoCheckPrototypeMaps(LCheckPrototypeMaps* instr) {
 
   ASSERT(prototypes->length() == maps->length());
 
-  for (int i = 0; i < prototypes->length(); i++) {
-    __ LoadHeapObject(reg, prototypes->at(i));
-    DoCheckMapCommon(reg, maps->at(i), ALLOW_ELEMENT_TRANSITION_MAPS, instr);
+  if (instr->hydrogen()->CanOmitPrototypeChecks()) {
+    for (int i = 0; i < maps->length(); i++) {
+      prototype_maps_.Add(maps->at(i), info()->zone());
+    }

[Toon Verwaest, 2013/02/13 10:40:07]

Is there a reason you copy the maps list, rather than just storing the pointer?

[ulan, 2013/02/13 12:27:38]

Yep, the prototype_maps_ list collects maps from many instr->maps().

+    __ LoadHeapObject(reg, prototypes->at(prototypes->length() - 1));

[Toon Verwaest, 2013/02/13 10:40:07]

Do all clients depend on this object being loaded? If not, we may want to look
into a way to remove this load as well. Perhaps in a different CL though.

[ulan, 2013/02/13 12:27:38]

The result is the holder and it is used in all callsites.

+  } else {
+    for (int i = 0; i < prototypes->length(); i++) {
+      __ LoadHeapObject(reg, prototypes->at(i));
+      DoCheckMapCommon(reg, maps->at(i), ALLOW_ELEMENT_TRANSITION_MAPS, instr);
+    }
   }
 }