Better range information for logical shift right >>>.

src/hydrogen-instructions.cc

 // Copyright 2011 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 1212 matching lines @@
           ? left()->range()->Copy()
           : new Range();
       result->Sar(c->Integer32Value());
       return result;
     }
   }
   return HValue::InferRange();
 }
 
 
+Range* HShr::InferRange() {
+  if (right()->IsConstant()) {
+    HConstant* c = HConstant::cast(right());
+    if (c->HasInteger32Value()) {
+      int shift_count = c->Integer32Value() & 0x1f;
+      if (left()->range()->CanBeNegative()) {
+        // Only compute bounds if the result always fits into an int32.
+        return (shift_count >= 1)
+            ? new Range(0, static_cast<uint32_t>(0xffffffff) >> shift_count)
+            : new Range();
+      } else {
+        // For positive inputs we can use the >> operator.
+        Range* result = (left()->range() != NULL)
+            ? left()->range()->Copy()
+            : new Range();
+        result->Sar(c->Integer32Value());
+        return result;
+      }
+    }
+  }
+  return HValue::InferRange();
+}
+
+
 Range* HShl::InferRange() {
   if (right()->IsConstant()) {
     HConstant* c = HConstant::cast(right());
     if (c->HasInteger32Value()) {
       Range* result = (left()->range() != NULL)
           ? left()->range()->Copy()
           : new Range();
       result->Shl(c->Integer32Value());
       return result;
     }
@@ skipping 574 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal