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

[Vladimir Kozlov]

Good.

Thanks,
Vladimir

On 5/8/20 1:45 AM, Christian Hagedorn wrote:
> 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/