Foundation for the use of informative definitions in Crankshaft.

src/hydrogen-instructions.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 756 matching lines @@
 }
 
 
 void HBoundsCheck::PrintDataTo(StringStream* stream) {
   index()->PrintNameTo(stream);
   stream->Add(" ");
   length()->PrintNameTo(stream);
 }
 
 
+void HBoundsCheck::InferRepresentation(HInferRepresentation* h_infer) {
+  ASSERT(CheckFlag(kFlexibleRepresentation));
+  Representation r;
+  if (key_mode_ == DONT_ALLOW_SMI_KEY ||
+      !length()->representation().IsTagged()) {
+    r = Representation::Integer32();
+  } else if (index()->representation().IsTagged() ||
+      (index()->IsConstant() &&
+       HConstant::cast(index())->HasInteger32Value() &&
+       Smi::IsValid(HConstant::cast(index())->Integer32Value()))) {
+    // If the index is tagged, or a constant that holds a Smi, allow the length
+    // to be tagged, since it is usually already tagged from loading it out of
+    // the length field of a JSArray. This allows for direct comparison without
+    // untagging.
+    r = Representation::Tagged();
+  } else {
+    r = Representation::Integer32();
+  }
+  UpdateRepresentation(r, h_infer, "boundscheck");
+}
+
+
 void HCallConstantFunction::PrintDataTo(StringStream* stream) {
   if (IsApplyFunction()) {
     stream->Add("optimized apply ");
   } else {
     stream->Add("%o ", function()->shared()->DebugName());
   }
   stream->Add("#%d", argument_count());
 }
 
 
@@ skipping 2052 matching lines @@
 
 
 void HCheckFunction::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal