A question about bytecodes

[John Rose]

On Jan 10, 2009, at 1:00 PM, Florian Weimer wrote:

> * John Rose:
>
>> The only way to tell for certain whether the optimizer has performed
>> escape analysis (or any other desired optimization) is to examine the
>> assembly code.  See:
>>   http://wikis.sun.com/display/HotSpotInternals/PrintAssembly
>
> Is there a reason why PrintOptoAssembly appears to be deprecated?
> Doesn't it contain additional type information which might be useful
> for debugging purposes (or just figuring out what's going on)?

I don't get "appears deprecated".  Do you mean that  
the .hotspot_compiler directive "print" is now called  
"printOptoAssembly", while "print" uses the PrintAssembly plugin if  
available?

PrintOptoAssembly still works and there are no plans for removing  
it.  It is a useful tool if you want a dump from the late stages of  
the server compiler.  It is not a true disassembler, however.  It  
prints scheduled machine-level graph nodes, not true assembly code.

Try PrintAssembly; it prints the real machine code as emitted after  
the compiler has finished.  It includes many interesting annotations,  
and it would be easy to add more.  If there is some type annotation  
in POA missing from PA, let's add it.

Caveat:  PrintAssembly requires you to create a separate module,  
based on Gnu binutils or an equivalent, which Sun people can't build  
for you, because the OpenJDK has to stay arms-length from any GPL-ed  
code that Sun do not own the rights to.  Some civic-minded non-Sun  
webmaster could build and host suitable PrintAssembly plugins, but  
Sun can't.  Alternatively, someone could cobble together an  
implementation of the plugin (for x86) which does not depend on  
binutils and contribute it to OpenJDK.  The plugin interface is  
beautifully simple, IMHO.  But that seems like more trouble than it's  
worth, given that binutils is freely available.

Best,
-- John