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Simon Peyton Jones authored
See Note [Do not eta-expand PAPs] in SimplUtils. This has a tremendously good effect on compile times for some simple benchmarks. The test is now where it belongs, in perf/compiler/T9020 (instead of simpl015). I did a nofib run and got essentially zero change except for cacheprof which gets 4% more allocation. I investigated. Turns out that we have instance PP Reg where pp ppm ST_0 = "%st" pp ppm ST_1 = "%st(1)" pp ppm ST_2 = "%st(2)" pp ppm ST_3 = "%st(3)" pp ppm ST_4 = "%st(4)" pp ppm ST_5 = "%st(5)" pp ppm ST_6 = "%st(6)" pp ppm ST_7 = "%st(7)" pp ppm r = "%" ++ map toLower (show r) That (map toLower (show r) does a lot of map/toLowers. But if we inline show we get something like pp ppm ST_0 = "%st" pp ppm ST_1 = "%st(1)" pp ppm ST_2 = "%st(2)" pp ppm ST_3 = "%st(3)" pp ppm ST_4 = "%st(4)" pp ppm ST_5 = "%st(5)" pp ppm ST_6 = "%st(6)" pp ppm ST_7 = "%st(7)" pp ppm EAX = map toLower (show EAX) pp ppm EBX = map toLower (show EBX) ...etc... and all those map/toLower calls can now be floated to top level. This gives a 4% decrease in allocation. But it depends on inlining a pretty big 'show' function. With this new patch we get slightly better eta-expansion, which makes a function look slightly bigger, which just stops it being inlined. The previous behaviour was luck, so I'm not going to worry about losing it. I've added some notes to nofib/Simon-nofib-notes
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