mboehme added a comment. To add to the points that @yurai007 pointed out, I’ve done some more investigation of my own.
**Compile-time regression does not seem to reproduce locally** Unfortunately, I still haven’t been able to get the test suite running locally. However, I’ve looked at some individual lencod input files which I’m able to compile and which still show a slowdown on http://llvm-compile-time-tracker.com/ even after https://reviews.llvm.org/D128097. What is confusing to me is that I am not able to reproduce the slowdown. For comparison, here are the instruction counts from http://llvm-compile-time-tracker.com/ and the counts I am measuring locally. At 7acc88be0312c721bc082ed9934e381d297f4707 <https://reviews.llvm.org/rG7acc88be0312c721bc082ed9934e381d297f4707> (the commit directly before https://reviews.llvm.org/D126061): | Input file | Tracker | Own measurement | | lencod/mb_access.c | 139M | 162,006,571 | | lencod/md_low.c | 227M | 264,179,977 | | At 0d300da799b06931eb6b974198d683548a8c8392 <https://reviews.llvm.org/rG0d300da799b06931eb6b974198d683548a8c8392> (the commit that landed https://reviews.llvm.org/D128097): | Input file | Tracker | Own measurement | | lencod/mb_access.c | 141M (+0.88%) | 161,322,974 (-0.42%) | | lencod/md_low.c | 228M (+0.57%) | 263,455,713 (-0.27%) | | Note that not only the direction of change is different, but also the absolute magnitude of instruction counts. I built Clang with `-DCMAKE_BUILD_TYPE=Release` and ran Clang with `-O0 -g -c -o /dev/null`. Maybe http://llvm-compile-time-tracker.com/ is doing something slightly different here? However, I suspect the more important factor for the direction of the change may be my local system headers, which are likely different to what http://llvm-compile-time-tracker.com/ is using. At any rate, this is frustrating because I’m not able to reproduce the issue. If it comes to it, would it be possible to obtain a preprocessed version of the input files (i.e. run with `-E`)? **Overall, compile times have //improved// in terms of cycle count (though not instruction count)** All of the above may be a moot point because I’ve noticed that the picture looks significantly different when looking at instructions versus cycle counts. The numbers I quoted in an earlier comment are for instruction counts (which is also the metric that @nikic used when originally raising this issue on https://reviews.llvm.org/D126061). Here are the same comparisons I showed earlier, with numbers taken from http://llvm-compile-time-tracker.com, but looking at cycle counts in addition to instruction counts (geomean for -O0 compiles in each case, titles link to the compile time tracker): Compile-time regression caused by D126061 <http://llvm-compile-time-tracker.com/compare.php?from=7acc88be0312c721bc082ed9934e381d297f4707&to=8c7b64b5ae2a09027c38db969a04fc9ddd0cd6bb&stat=instructions> Instructions: +0.35% Cycles: +0.30% Improvement due to this patch (D128097) <http://llvm-compile-time-tracker.com/compare.php?from=1c2b756cd6f9f9408863fb0e91f55731f81b46d9&to=0d300da799b06931eb6b974198d683548a8c8392&stat=instructions> Instructions: -0.18% Cycles: -1.54% Cumulative change from before D126061 landed until after this patch (D128097) landed <http://llvm-compile-time-tracker.com/compare.php?from=7acc88be0312c721bc082ed9934e381d297f4707&to=0d300da799b06931eb6b974198d683548a8c8392&stat=instructions> Instructions: +0.22% Cycles: -1.09% So in terms of cycle count, which is arguably the more important metric, the overall effect of the two changes is over 1% improvement in compile times. It would of course be great if we could reduce the regression on instruction counts too, but given that we have a marked improvement in cycle count, I think that may already be an acceptable result? @nikic, I would appreciate your input here. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D128097/new/ https://reviews.llvm.org/D128097 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
