https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84402
--- Comment #69 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Tamar Christina <tnfch...@gcc.gnu.org>: https://gcc.gnu.org/g:703417a030b3d80f55ba1402adc3f1692d3631e5 commit r14-500-g703417a030b3d80f55ba1402adc3f1692d3631e5 Author: Tamar Christina <tamar.christ...@arm.com> Date: Fri May 5 13:38:50 2023 +0100 match.pd: automatically partition *-match.cc files. Following on from Richi's RFC[1] this is another attempt to split up match.pd into multiple gimple-match and generic-match files. This version is fully automated and requires no human intervention. First things first, some perf numbers. The following shows the effect of the patch on my desktop doing parallel compilation of gimple-match: +--------+------------------+--------+------------------+ | splits | rel. improvement | splits | rel. improvement | +--------+------------------+--------+------------------+ | 1 | 0.00% | 33 | 91.03% | | 2 | 71.77% | 34 | 84.02% | | 3 | 100.71% | 35 | 83.42% | | 4 | 143.08% | 36 | 78.80% | | 5 | 176.18% | 37 | 74.06% | | 6 | 174.40% | 38 | 55.76% | | 7 | 176.62% | 39 | 66.90% | | 8 | 168.35% | 40 | 18.25% | | 9 | 189.80% | 41 | 16.55% | | 10 | 171.77% | 42 | 47.02% | | 11 | 152.82% | 43 | 15.29% | | 12 | 112.20% | 44 | 21.63% | | 13 | 158.57% | 45 | 41.53% | | 14 | 158.57% | 46 | 21.98% | | 15 | 152.07% | 47 | -42.74% | | 16 | 151.70% | 48 | -32.62% | | 17 | 131.52% | 49 | 11.81% | | 18 | 133.11% | 50 | 34.07% | | 19 | 137.33% | 51 | 2.71% | | 20 | 103.83% | 52 | -22.23% | | 21 | 132.47% | 53 | 32.30% | | 22 | 116.52% | 54 | 21.45% | | 23 | 112.73% | 55 | 40.02% | | 24 | 111.94% | 56 | 42.83% | | 25 | 112.73% | 57 | -9.98% | | 26 | 104.07% | 58 | 18.01% | | 27 | 113.27% | 59 | -4.91% | | 28 | 96.77% | 60 | 22.94% | | 29 | 93.42% | 61 | -3.73% | | 30 | 87.67% | 62 | -27.43% | | 31 | 89.54% | 63 | -1.05% | | 32 | 84.42% | 64 | -5.44% | +--------+------------------+--------+------------------+ As can be seen there seems to be a point of diminishing returns in doing splits. This comes from the fact that these match files consume a sizeable amount of headers. At a certain point the parsing overhead of the headers dominate and you start losing in gains. As such from this I've made the default 10 splits per file to allow for some room for growth in the future without needing changes to the split amount. Since 5-10 show roughly the same gains it means we can afford to double the file sizes before we need to up the split amount. This can be controlled by the configure parameter --with-matchpd-partitions=. At 10 splits the sizes of the files are: 1.2M gimple-match-1.cc 490K gimple-match-2.cc 459K gimple-match-3.cc 462K gimple-match-4.cc 466K gimple-match-5.cc 690K gimple-match-6.cc 517K gimple-match-7.cc 693K gimple-match-8.cc 1011K gimple-match-9.cc 490K gimple-match-10.cc 210K gimple-match-auto.h The reason gimple-match-1.cc is so large is because it got allocated a very large function: gimple_simplify_NE_EXPR. Because of these sporadically large functions the allocation to a split happens based on the amount of data already written to a split instead of just a simple round robin allocation (though the patch supports that too.). This means that once gimple_simplify_NE_EXPR is allocated to gimple-match-1.cc nothing uses it again until the rest of the files catch up. To support this split a new header file *-match-auto.h is generated to allow the individual files to compile separately. Lastly for the auto generated files I use pragmas to silence the unused predicate warnings instead of the previous Makefile way because I couldn't find a way to set them without knowing the number of split files beforehand. Finally with this change, bootstrap time has dropped 8 minutes on AArch64. [1] https://gcc.gnu.org/legacy-ml/gcc-patches/2018-04/msg01125.html gcc/ChangeLog: PR bootstrap/84402 * genmatch.cc (emit_func, SIZED_BASED_CHUNKS, get_out_file): New. (decision_tree::gen): Accept list of files instead of single and update to write function definition to header and main file. (write_predicate): Likewise. (write_header): Emit pragmas and new includes. (main): Create file buffers and cleanup. (showUsage, write_header_includes): New.
