[LLVMdev] InstCombine adds bit masks, confuses self, others

[Jakob Stoklund Olesen]

On Apr 16, 2012, at 3:30 PM, Chandler Carruth <chandlerc at google.com> wrote:

> Does sinking these into the DAGCombine layer help? How much does it break?

I tried disabling just the InstCombine transforms that hide shl instructions behind bitmasks. Even though DAGCombine has the same transforms, it causes some pretty bad regressions:

External/SPEC/CINT95/147_vortex/147_vortex                                   0.294   0.322   +9.6%  +40mB
MultiSource/Benchmarks/Olden/tsp/tsp                                         0.680   0.748   +9.9%  +41mB
SingleSource/Benchmarks/Shootout-C++/except                                  0.116   0.128  +10.8%  +45mB
SingleSource/Benchmarks/Shootout/strcat                                      0.102   0.113  +11.1%  +46mB
SingleSource/Benchmarks/Shootout-C++/hash                                    0.455   0.507  +11.4%  +47mB
External/Povray/povray                                                       2.015   2.246  +11.5%  +47mB
External/SPEC/CINT2000/255_vortex/255_vortex                                 1.814   2.044  +12.7%  +52mB
SingleSource/Benchmarks/Shootout-C++/heapsort                                1.871   2.132  +13.9%  +57mB
SingleSource/Benchmarks/Shootout-C++/ary3                                    1.087   1.264  +16.3%  +65mB
MultiSource/Benchmarks/SciMark2-C/scimark2                                  27.491  23.596  -14.2%  -66mB
MultiSource/Benchmarks/Olden/bisort/bisort                                   0.360   0.428  +19.0%  +75mB
MultiSource/Benchmarks/Olden/bh/bh                                           1.074   1.287  +19.9%  +79mB

(Running on Sandy Bridge, x86-64)

I'll try to figure out why.

/jakob

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