RFR: 8346888: [ubsan] block.cpp:1617:30: runtime error: 9.97582e+36 is outside the range of representable values of type 'int'

[Roberto Castañeda Lozano]

On Thu, 20 Mar 2025 15:44:31 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> There may be a bug in frequency propagation.  I don't understand the connector/non-connector logic, but when I reproduce this, the successor has a loop block with high _freq, but then we use non_connector_successor() to get the successor, and that gives us instead a different block which originally had 0 _freq, but got changed to MIN_BLOCK_FREQUENCY by CFGLoop::scale_freq().
>
> Could the problem be inconsistent use of non_connector_successor?  Isn't there some logic which forces deopt blocks to have low frequencies?  It it's only setting the non_connector_successor frequency then you'd get inconsistent results if you didn't use non_connector_successor for examining successors.  Maybe it should be adjusting the frequency of all blocks leading to the non_connector_successor?

> There may be a bug in frequency propagation.

I haven't looked at these failures but could it have to do with irreducible loops? This is a known reason of frequency propagation inaccuracy in C2, see [JDK-8258895](https://bugs.openjdk.org/browse/JDK-8258895).

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PR Review Comment: https://git.openjdk.org/jdk/pull/23962#discussion_r2006175477