38a5ec5fca
The primary motivation for the change is that FindMatchLength is likely to discover a difference in the first 8 bytes it compares. If that occurs then we know the length of the match is less than 12, because FindMatchLength is invoked after a 4-byte match is found. When emitting a copy, it is useful to know that the length is less than 12 because the two-byte variant of an emitted copy requires that. This is a performance-tuning change that should not affect the library's behavior. With FDO on perflab/Haswell the geometric mean for ZFlat/* went from 47,290ns to 45,741ns, an improvement of 3.4%. SAMPLE (before) BM_ZFlat/0 102824 102650 40691 951.4MB/s html (22.31 %) BM_ZFlat/1 1293512 1290442 3225 518.9MB/s urls (47.78 %) BM_ZFlat/2 10373 10353 417959 11.1GB/s jpg (99.95 %) BM_ZFlat/3 268 268 15745324 712.4MB/s jpg_200 (73.00 %) BM_ZFlat/4 12137 12113 342462 7.9GB/s pdf (83.30 %) BM_ZFlat/5 430672 429720 9724 909.0MB/s html4 (22.52 %) BM_ZFlat/6 420541 419636 9833 345.6MB/s txt1 (57.88 %) BM_ZFlat/7 373829 373158 10000 319.9MB/s txt2 (61.91 %) BM_ZFlat/8 1119014 1116604 3755 364.5MB/s txt3 (54.99 %) BM_ZFlat/9 1544203 1540657 2748 298.3MB/s txt4 (66.26 %) BM_ZFlat/10 91041 90866 46002 1.2GB/s pb (19.68 %) BM_ZFlat/11 332766 331990 10000 529.5MB/s gaviota (37.72 %) BM_ZFlat/12 39960 39886 100000 588.3MB/s cp (48.12 %) BM_ZFlat/13 14493 14465 287181 735.1MB/s c (42.47 %) BM_ZFlat/14 4447 4440 947927 799.3MB/s lsp (48.37 %) BM_ZFlat/15 1316362 1313350 3196 747.7MB/s xls (41.23 %) BM_ZFlat/16 312 311 10000000 613.0MB/s xls_200 (78.00 %) BM_ZFlat/17 388471 387502 10000 1.2GB/s bin (18.11 %) BM_ZFlat/18 65 64 64838208 2.9GB/s bin_200 (7.50 %) BM_ZFlat/19 65900 65787 63099 554.3MB/s sum (48.96 %) BM_ZFlat/20 6188 6177 681951 652.6MB/s man (59.21 %) SAMPLE (after) Benchmark Time(ns) CPU(ns) Iterations -------------------------------------------- BM_ZFlat/0 99259 99044 42428 986.0MB/s html (22.31 %) BM_ZFlat/1 1257039 1255276 3341 533.4MB/s urls (47.78 %) BM_ZFlat/2 10044 10030 405781 11.4GB/s jpg (99.95 %) BM_ZFlat/3 268 267 15732282 713.3MB/s jpg_200 (73.00 %) BM_ZFlat/4 11675 11657 358629 8.2GB/s pdf (83.30 %) BM_ZFlat/5 420951 419818 9739 930.5MB/s html4 (22.52 %) BM_ZFlat/6 415460 414632 10000 349.8MB/s txt1 (57.88 %) BM_ZFlat/7 367191 366436 10000 325.8MB/s txt2 (61.91 %) BM_ZFlat/8 1098345 1096036 3819 371.3MB/s txt3 (54.99 %) BM_ZFlat/9 1508701 1505306 2758 305.3MB/s txt4 (66.26 %) BM_ZFlat/10 87195 87031 47289 1.3GB/s pb (19.68 %) BM_ZFlat/11 322338 321637 10000 546.5MB/s gaviota (37.72 %) BM_ZFlat/12 36739 36668 100000 639.9MB/s cp (48.12 %) BM_ZFlat/13 13646 13618 304009 780.9MB/s c (42.47 %) BM_ZFlat/14 4249 4240 992456 837.0MB/s lsp (48.37 %) BM_ZFlat/15 1262925 1260012 3314 779.4MB/s xls (41.23 %) BM_ZFlat/16 308 308 10000000 619.8MB/s xls_200 (78.00 %) BM_ZFlat/17 379750 378944 10000 1.3GB/s bin (18.11 %) BM_ZFlat/18 62 62 67443280 3.0GB/s bin_200 (7.50 %) BM_ZFlat/19 61706 61587 67645 592.1MB/s sum (48.96 %) BM_ZFlat/20 5968 5958 698974 676.6MB/s man (59.21 %)
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