[9] RFR(S): 8072398: assert fails in L1RGenerator::increment_event_counter_impl

[Zoltán Majó]

Hi,


please review the following small patch.

Bug: https://bugs.openjdk.java.net/browse/JDK-8072398

Problem: The reported assert is triggered because the method 
LIRGenerator::increment_event_counter_impl is called with parameter 
'frequency' set to -1.

The value originates from Arguments::scaled_freq_log(): If both 
variables 'freq_log' and 'scale' are small, 'scaled_freq' can become 0 
and the function log2_intptr returns -1 for the value 0. A similar 
problem appears if freq_log == 0.


Solution:

To treat the above mentioned cases graciously, this patch:

- Changes Arguments::scaled_freq_log() and 
Arguments::scaled_compile_threshold() to allow scaling the 
frequency/threshold by 0.0 and return 0.0 in these cases without calling 
log2_intptr().

- Adds a new condition to Arguments::set_tiered_flags(): Threshold 
values are *not scaled* if 'CompileThresholdScaling' is 0.0 (behavior 
equivalent to -Xint). Previously, this functionality was encoded in 
scaled_freq_log() and scaled_compile_threshold(). Handling this case in 
set_tiered_flags() results in clearer code.

- Improves comments.


Webrev: http://cr.openjdk.java.net/~zmajo/8072398/webrev.00/

Testing:
- manual testing with failing test cases
- compiler/arguments/CheckCompileThresholdScaling.java
- JPRT

Thank you and best regards,


Zoltan