Bug 154207 – Load + Register Extend should be simplified into Load

• Component: JavaScriptCore
• Status: NEW

[Benjamin Poulain]

This:
@1 = Load(@x);
@2 = SExt8(@1)

should be transformed as:
@3 = Load8(@x)

This must be done at B3 level instead of lowering in order to have the address go through legalizeMemoryOffsets().

[Filip Pizlo]

(In reply to comment #0)
> This:
> @1 = Load(@x);
> @2 = SExt8(@1)
> 
> should be transformed as:
> @3 = Load8(@x)
> 
> This must be done at B3 level instead of lowering in order to have the
> address go through legalizeMemoryOffsets().

Seems like we "just" need use counts to do this, so we prove that the Load is not used for anything else.  reduceStrength() could almost do it, but it would be dangerous, since that phase modifies the IR as it goes - so it will probably mess up any use count calculations.

That implies that we should add a new phase to do this.  This phase should probably also get other things that require use counts.

[Benjamin Poulain]

Created attachment 272741 [details]
Patch

[WebKit Commit Bot]

Attachment 272741 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/b3/testb3.cpp:5560:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5578:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5620:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5621:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5635:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5636:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5651:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5653:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5667:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5668:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5682:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5683:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5697:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5698:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5713:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5715:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5729:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:5730:  Consider using CHECK_EQ instead of CHECK(a == b)  [readability/check] [2]
Total errors found: 18 in 9 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Alex Christensen]

Comment on attachment 272741 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=272741&action=review

> Source/JavaScriptCore/b3/B3ReduceLoadStrength.cpp:2
> + * Copyright (C) 2015 Apple Inc. All rights reserved.

nit: 2016

[Benjamin Poulain]

Oddly, this looks neutral on ARM64.

                                                  Conf#1                    Conf#2                                      
SunSpider:
   3d-cube                                   10.4225+-0.0819     ?     10.4328+-0.0886        ?
   3d-morph                                   8.3399+-0.1316            8.3179+-0.0621        
   3d-raytrace                                9.5516+-0.3255            9.5405+-0.3488        
   access-binary-trees                        4.3262+-0.2322     ?      4.3801+-0.0600        ? might be 1.0125x slower
   access-fannkuch                           11.5094+-0.3124           11.4914+-0.2874        
   access-nbody                               4.7831+-0.0301            4.7522+-0.0290        
   access-nsieve                              3.4041+-0.0409     ?      3.4456+-0.0558        ? might be 1.0122x slower
   bitops-3bit-bits-in-byte                   1.7092+-0.0215     ?      1.7697+-0.1189        ? might be 1.0354x slower
   bitops-bits-in-byte                        4.1934+-0.0406            4.1794+-0.0285        
   bitops-bitwise-and                         3.2763+-0.0777            3.2463+-0.0582        
   bitops-nsieve-bits                         5.9133+-0.0633            5.9008+-0.0456        
   controlflow-recursive                      3.7743+-0.2521            3.7358+-0.3400          might be 1.0103x faster
   crypto-aes                                 6.4744+-0.0808            6.4397+-0.0534        
   crypto-md5                                 4.0788+-0.1389     ?      4.2801+-0.3735        ? might be 1.0494x slower
   crypto-sha1                                3.7694+-0.0639     ?      3.7959+-0.1367        ?
   date-format-tofte                         11.2938+-0.0841     ?     11.3011+-0.0991        ?
   date-format-xparb                          7.3490+-0.1118     ?      7.3584+-0.1007        ?
   math-cordic                                5.4631+-0.0912            5.4425+-0.1090        
   math-partial-sums                         11.6965+-0.1031     ?     11.7500+-0.0898        ?
   math-spectral-norm                         3.5078+-0.2203            3.3322+-0.2333          might be 1.0527x faster
   regexp-dna                                 9.7854+-0.0681            9.7693+-0.0664        
   string-base64                              6.5219+-0.0450            6.5099+-0.0299        
   string-fasta                               9.6279+-0.3293     ?      9.6350+-0.2924        ?
   string-tagcloud                           11.0055+-0.2440     ?     11.0197+-0.1790        ?
   string-unpack-code                        23.4390+-0.0882           23.3442+-0.0803        
   string-validate-input                      6.4305+-0.1878     ?      6.5413+-0.1407        ? might be 1.0172x slower

   <arithmetic>                               7.3710+-0.0179     ?      7.3735+-0.0319        ? might be 1.0003x slower

                                                  Conf#1                    Conf#2                                      
Octane:
   encrypt                                   0.19687+-0.00067    ?     0.19781+-0.00148       ?
   decrypt                                   3.72317+-0.00911          3.71527+-0.00690       
   deltablue                        x2       0.17056+-0.00089    ?     0.17340+-0.00418       ? might be 1.0167x slower
   earley                                    0.42355+-0.00966    ?     0.42556+-0.01110       ?
   boyer                                     7.39531+-0.12680    ?     7.54110+-0.26902       ? might be 1.0197x slower
   navier-stokes                    x2       7.18109+-0.00599          7.17997+-0.00690       
   raytrace                         x2       1.28817+-0.00785    ?     1.30752+-0.03433       ? might be 1.0150x slower
   richards                         x2       0.11298+-0.00289    ?     0.11326+-0.00194       ?
   splay                            x2       0.72602+-0.01767    ?     0.72802+-0.01090       ?
   regexp                           x2      34.90936+-0.12731         34.81403+-0.12786       
   pdfjs                            x2      57.28040+-0.24741         57.15629+-0.34824       
   mandreel                         x2      71.03873+-0.86106         70.69574+-1.02180       
   gbemu                            x2      46.46087+-3.14811    ?    51.50368+-5.56189       ? might be 1.1085x slower
   closure                                   0.65471+-0.00954          0.65139+-0.00274       
   jquery                                    9.62274+-0.02646          9.62142+-0.04047       
   box2d                            x2      16.09526+-0.16333         16.02558+-0.09420       
   zlib                             x2     683.23024+-31.72146       672.21808+-37.34598        might be 1.0164x faster
   typescript                       x2    1141.30809+-4.78125    ?  1144.27098+-8.93657       ?

   <geometric>                               8.07399+-0.04610    ?     8.13484+-0.06335       ? might be 1.0075x slower

                                                  Conf#1                    Conf#2                                      
Kraken:
   ai-astar                                  156.768+-2.865            156.533+-2.479         
   audio-beat-detection                       77.603+-5.235      ?      79.476+-4.149         ? might be 1.0241x slower
   audio-dft                                 150.311+-6.566            142.803+-5.301           might be 1.0526x faster
   audio-fft                                  41.889+-0.106      ?      41.990+-0.211         ?
   audio-oscillator                           54.419+-0.656             54.144+-0.163         
   imaging-darkroom                           69.249+-0.222             69.208+-0.174         
   imaging-desaturate                         78.500+-0.796      ?      78.953+-1.253         ?
   imaging-gaussian-blur                      98.852+-0.486             98.127+-1.138         
   json-parse-financial                       47.499+-0.216             47.251+-0.261         
   json-stringify-tinderbox                   27.298+-0.118             27.089+-0.144         
   stanford-crypto-aes                        58.808+-0.255      ?      59.165+-0.511         ?
   stanford-crypto-ccm                        46.773+-0.881             46.543+-0.780         
   stanford-crypto-pbkdf2                    141.222+-0.537      ?     141.414+-1.004         ?
   stanford-crypto-sha256-iterative           51.213+-0.142             51.042+-0.168         

   <arithmetic>                               78.600+-0.522             78.124+-0.530           might be 1.0061x faster

                                                  Conf#1                    Conf#2                                      
AsmBench:
   bigfib.cpp                               725.7208+-29.8290    ?    734.5102+-20.2056       ? might be 1.0121x slower
   cray.c                                   559.5356+-4.5890     ?    563.1744+-5.9183        ?
   dry.c                                    471.0161+-3.8902     ?    472.3592+-2.9768        ?
   FloatMM.c                                810.2771+-8.9211          805.1089+-9.3111        
   gcc-loops.cpp                           4675.4980+-24.6400        4661.7415+-3.5747        
   n-body.c                                1762.1646+-2.4270     ?   1762.2233+-3.8443        ?
   Quicksort.c                              561.8582+-2.4384          560.1319+-3.1790        
   stepanov_container.cpp                  5636.6802+-23.4988    ?   5639.4599+-17.3435       ?
   Towers.c                                 277.4103+-1.1818     ?    277.5199+-1.6721        ?

   <geometric>                             1012.6144+-5.2120     ?   1013.8331+-3.6487        ? might be 1.0012x slower

                                                  Conf#1                    Conf#2                                      
Geomean of preferred means:
   <scaled-result>                           46.6509+-0.0970     ?     46.6853+-0.1113        ? might be 1.0007x slower