[15] RFR(M): 8244207: Simplify usage of Compile::print_method() when debugging with gdb and enable its use with rr

[Christian Hagedorn]

Thank you Vladimir and Tobias for your reviews!

On 08.05.20 08:24, Tobias Hartmann wrote:
> looks good to me too but please use (jio_)snprintf instead of unsafe sprintf.

Thinking of which, we could probably directly use the phase_name 
parameter and call print_method() without allocating a char array and 
using jio_snprintf. However, it might be a good idea to change sprintf 
into jio_snprintf in Compile::print_method (where I got this code from). 
There it makes sense to use an additional char array to concatenate two 
strings.

I included those changes together with the typo fix in a new webrev:
http://cr.openjdk.java.net/~chagedorn/8244207/webrev.01/

Best regards,
Christian

> On 07.05.20 20:38, Vladimir Kozlov wrote:
>> Looks good.
>>
>> Thanks,
>> Vladimir
>>
>> On 5/7/20 5:09 AM, Christian Hagedorn wrote:
>>> Hi
>>>
>>> Please review the following debugging enhancement:
>>> https://bugs.openjdk.java.net/browse/JDK-8244207
>>> http://cr.openjdk.java.net/~chagedorn/8244207/webrev.00/
>>>
>>> This enhancement simplifies the usage for printing the ideal graph for visualization with the
>>> Ideal Graph Visualizer when debugging with gdb and enables graph printing with rr [1].
>>>
>>> Instead of calling Compile::current()->print_method(PHASE_X, y, z) from gdb, one can now just call
>>> igv_print() or igv_print(phase_name) with a custom phase name. There are multiple options
>>> depending on where the graph should be printed to (file or over network/locally to an opened Ideal
>>> Graph Visualizer). When choosing file, the output is always printed to a file named
>>> custom_debug.xml. I think the flexibility to choose another file name is not really required since
>>> it's only used while debugging. These new igv_print() methods can also be called from gdb without
>>> setting any flags required for the usual calls to Compile::current()->print_method(PHASE_X, y, z)
>>> to work.
>>>
>>> The standard Compile::current()->print_method(PHASE_X, y, z) call does not work while debugging a
>>> program trace with rr (and is probably also problematic with related replay tools). The call gets
>>> stuck somewhere. rr allows to alter some data at a breakpoint but as soon as execution continues
>>> on the replayed trace, the modifications are undone (except for file writes). This enhancement
>>> also addresses this such that the new igv_print() methods can be used with rr. However, when
>>> printing to a file is chosen, igv_print() will overwrite custom_debug.xml again at the next
>>> execution stop. To avoid that I added additional rr-specific igv_append() and
>>> igv_append(phase_name) methods that simply append a graph to the existing custom_debug.xml file
>>> without setting up a file header again. This allows all printed graphs to be kept in one file
>>> which makes it easier to navigate through them.
>>>
>>> Thank you!
>>>
>>> Best regards,
>>> Christian
>>>
>>>
>>> [1] https://rr-project.org/