#14951: SpecConstr needs two runs when one should suffice -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: task | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #14844 | Differential Rev(s): Phab:D4519 Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): Ok, here is some very motivation data: If I run !SpecConstr twice, with simplification in between (and without the patch in Phab:D4519), then there are significant performance improvements: {{{ Nofib allocations Benchmark name previous change now nofib/allocs/event 129683224 + 8.44% 140627312 bytes nofib/allocs/fulsom 243329632 - 7.83% 224287920 bytes nofib/allocs/mandel2 922640 - 13.89% 794448 bytes nofib/allocs/minimax 5371584 - 8.73% 4902576 bytes nofib/allocs/parstof 3038584 - 3.63% 2928248 bytes Nofib instruction Benchmark name previous change now nofib/instr/compress2 549006516 - 6.36% 514104497 nofib/instr/fulsom 755145483 - 3.41% 729394470 nofib/instr/ida 261218740 - 3.98% 250820469 nofib/instr/k-nucleotide 2140743692 - 3.97% 2055743369 nofib/instr/minimax 9099200 - 4.38% 8700706 }}} I checked that these are really due to the second !SpecConstr (and not due to the extra simplification). I did not investigate them individually, and unfortunately, Phab:D4519 does _not_ achieve any of these improvements. Is there a reasonably simple way to make !SpecConstr more idempotent? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14951#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler