Request for reviews (M): 7170463: C2 should recognize "obj.getClass() == A.class" code pattern

[John Rose]

On May 23, 2012, at 4:47 PM, Vladimir Kozlov wrote:

> I updated webrev:
> 
> http://cr.openjdk.java.net/~kvn/7170463/webrev.01
> 
> I found additional issue with original changes. They accidentally removed optimization which replaces LoadKlass node with ConP (klass type) in map. Next code will not be executed:
> 
>   cast = con;  // Replace non-constant val by con.
> 
> New code should do separate map update of object which klass is compared.

That's fine; I like it.

New question:  Can the following call return Top?
  obj_type->join(con_type)

E.g.,
  Number x = 5;
  if (x.getClass() == String.class)
    System.out.println("fail!");

Perhaps the compare will short-circuit before that happens.  If it doesn't, we'll get assertion failures or worse.

— John
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