[llvm-branch-commits] [llvm] [LoopVectorizer] Prune VFs based on plan register pressure (PR #132190)

[Luke Lau via llvm-branch-commits]

lukel97 wrote:

I collected some more data on RISC-V on SPEC CPU 2017, this improves code size by up to 7% on some benchmarks, and no regressions were found: https://lnt.lukelau.me/db_default/v4/nts/399?show_delta=yes&show_previous=yes&show_stddev=yes&show_mad=yes&show_all=yes&show_all_samples=yes&show_sample_counts=yes&show_small_diff=yes&num_comparison_runs=0&test_filter=&test_min_value_filter=&aggregation_fn=min&MW_confidence_lv=0.05&compare_to=401&submit=Update

There's also a significant decrease in vector spilling and reloading. It removes all the spilling entirely on one benchmark so the geomean result is stuck at 100%:

```
Program                                       riscv-instr-info.NumVRegReloaded                 riscv-instr-info.NumVRegSpilled                
                                              lhs                              rhs     diff    lhs                             rhs     diff   
FP2017rate/508.namd_r/508.namd_r                 6.00                             6.00    0.0%    1.00                            1.00    0.0%
INT2017rat...00.perlbench_r/500.perlbench_r      8.00                             8.00    0.0%    4.00                            4.00    0.0%
INT2017speed/625.x264_s/625.x264_s              35.00                            35.00    0.0%   39.00                           39.00    0.0%
INT2017spe...23.xalancbmk_s/623.xalancbmk_s      6.00                             6.00    0.0%    6.00                            6.00    0.0%
INT2017spe...ed/620.omnetpp_s/620.omnetpp_s      5.00                             5.00    0.0%    4.00                            4.00    0.0%
INT2017speed/602.gcc_s/602.gcc_s                70.00                            70.00    0.0%   64.00                           64.00    0.0%
INT2017spe...00.perlbench_s/600.perlbench_s      8.00                             8.00    0.0%    4.00                            4.00    0.0%
INT2017rate/525.x264_r/525.x264_r               35.00                            35.00    0.0%   39.00                           39.00    0.0%
INT2017rat...23.xalancbmk_r/523.xalancbmk_r      6.00                             6.00    0.0%    6.00                            6.00    0.0%
INT2017rate/520.omnetpp_r/520.omnetpp_r          5.00                             5.00    0.0%    4.00                            4.00    0.0%
INT2017rate/502.gcc_r/502.gcc_r                 70.00                            70.00    0.0%   64.00                           64.00    0.0%
FP2017speed/644.nab_s/644.nab_s                 24.00                            24.00    0.0%   24.00                           24.00    0.0%
FP2017rate/544.nab_r/544.nab_r                  24.00                            24.00    0.0%   24.00                           24.00    0.0%
FP2017rate/511.povray_r/511.povray_r           131.00                           131.00    0.0%   74.00                           74.00    0.0%
FP2017rate/510.parest_r/510.parest_r          1490.00                          1484.00   -0.4% 1231.00                         1225.00   -0.5%
INT2017rat...31.deepsjeng_r/531.deepsjeng_r    248.00                           218.00  -12.1%  134.00                          102.00  -23.9%
INT2017spe...31.deepsjeng_s/631.deepsjeng_s    248.00                           218.00  -12.1%  134.00                          102.00  -23.9%
FP2017rate/526.blender_r/526.blender_r        1210.00                           703.00  -41.9% 1033.00                          654.00  -36.7%
FP2017speed/638.imagick_s/638.imagick_s       7524.00                          1486.00  -80.2% 4813.00                          925.00  -80.8%
FP2017rate/538.imagick_r/538.imagick_r        7524.00                          1486.00  -80.2% 4813.00                          925.00  -80.8%
FP2017speed/619.lbm_s/619.lbm_s                 42.00                             0.00 -100.0%   42.00                                 -100.0%
FP2017rate/519.lbm_r/519.lbm_r                  42.00                             0.00 -100.0%   42.00                                 -100.0%
FP2017rate...97.specrand_fr/997.specrand_fr      0.00                             0.00                                                        
FP2017spee...96.specrand_fs/996.specrand_fs      0.00                             0.00                                                        
INT2017rate/505.mcf_r/505.mcf_r                  0.00                             0.00                                                        
INT2017rate/541.leela_r/541.leela_r              0.00                             0.00                                                        
INT2017rate/557.xz_r/557.xz_r                    0.00                             0.00                                                        
INT2017rat...99.specrand_ir/999.specrand_ir      0.00                             0.00                                                        
INT2017speed/605.mcf_s/605.mcf_s                 0.00                             0.00                                                        
INT2017speed/641.leela_s/641.leela_s             0.00                             0.00                                                        
INT2017speed/657.xz_s/657.xz_s                   0.00                             0.00                                                        
INT2017spe...98.specrand_is/998.specrand_is      0.00                             0.00                                                        
                           Geomean difference                                          -100.0%                                          -19.4%
```


https://github.com/llvm/llvm-project/pull/132190