review request (S): 6981788 GC map generator sometimes picks up the wrong kind of instruction operand

[Tom Rodriguez]

On Oct 23, 2010, at 12:04 AM, John Rose wrote:

> 6981788: GC map generator sometimes picks up the wrong kind of instruction operand
> Summary: Distinguish pool indexes from cache indexes in recently changed code.
> http://cr.openjdk.java.net/~jrose/6981788/webrev.00

I don't understand this line:

+        int idx = currentBC->has_index_u4() ? currentBC->get_index_u4() : currentBC->get_index_u2_cpcache();

idx is used to index into the constant pool immediately after, so why is it asking for cpcache?

Also why is this right?

+  bool            ref = ldc->has_cache_index() || cp->is_pointer_entry(ldc->pool_index());

What does has_cache_index have to do with ref'ness?

tom

> 
> The bug reproduces with ScavengeALot on an invokedynamic instruction and on a fast_aldc instruction (ldc/MH).  
> 
> Verified the fix.  Tried it with and without TraceNewOopMapGeneration.
> 
> -- John