[16] RFR(S): 8251093: Improve C1 register allocator logging and debugging support

[Vladimir Kozlov]

One note. Most of the code is guarded by #ifndef PRODUCT.

But the flag is available only in DEBUG build:
   develop(intx, TraceLinearScanLevel, 0,

Should we use #ifdef ASSERT and DEBUG() instead?

Thanks,
Vladimir

On 8/14/20 5:10 AM, Christian Hagedorn wrote:
> Hi
> 
> Please review the following enhancement for C1:
> https://bugs.openjdk.java.net/browse/JDK-8251093
> http://cr.openjdk.java.net/~chagedorn/8251093/webrev.00/
> 
> While I was working on JDK-8249603 [1], I added some additional debugging and logging code which helped to figure out 
> what was going on. I think it would be useful to have this code around for the analysis of future C1 register allocator 
> bugs.
> 
> This RFE adds (everything non-product code):
> - find_interval(number): Can be called like that from gdb anywhere to find an interval with the given number.
> - Interval::print_children()/print_parent(): Useful when debugging with gdb to quickly show the split children and parent.
> - LinearScan::print_reg_num(number): Prints the register or stack location for this register number. This is useful in 
> some places (logging with TraceLinearScanLevel set) where it just printed a number which first had to be manually looked 
> up in other logs.
> 
> I additionally did some cleanup of the touched code.
> 
> We could additionally split the TraceLinearScanLevel flag into separate flags related to the different phases of the 
> register allocation algorithm. It currently just prints too much details on the higher levels. You often find yourself 
> being interested in a specific part of the algorithm and only want to know more details there. To achieve that you now 
> you have to either handle all the noise or manually disable/enable other logs. We could file an RFE to clean this up if 
> it's worth the effort - given that there are not many new issues filed for C1 register allocation today.
> 
> Thank you!
> 
> Best regards,
> Christian
> 
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8251093
>