[PATCH] D140635: Enabled DFAJumpThreading by Default

Thu Dec 29 13:42:29 PST 2022

nikic requested changes to this revision.
nikic added a comment.
This revision now requires changes to proceed.

In D140635#4019565 <https://reviews.llvm.org/D140635#4019565>, @amehsan wrote:

>> This is much more expensive than when I tested this the last time on August 2nd, 2021: https://llvm-compile-time-tracker.com/compare.php?from=380b8a603c6e8997819726b15a76b8f6c94aa21a&to=abb759c879725b7bc09a466e92c9b9eca7f8f483&stat=instructions:u At that time, the pass was pretty cheap, and as such a reasonable tradeoff. Now this doesn't seem to be the case anymore.
>
> Taking the geomean of compile time change in the above table shows 0.23% increase in compile time. That is not acceptable?

Not sure how you arrived at that number (isn't it 0.44% geomean across optimized builds?), but no, these regressions are not acceptable for what the pass does, especially if we already know that it can be much faster.

Some of the regressions might be due to second-order effects (i.e. the transform triggers, and this affects compile-time of other transforms), but there are some really large regressions without code size changes, which indicate that the pass itself is slow. For example libclamav_regex_regexec.c has a 16% regression, configfile.c has a 12% regression and header.c has a 17% regression, all without changes in code size.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140635/new/

https://reviews.llvm.org/D140635