#7782: flag to run the demand analysis a second time ----------------------------+---------------------------------------------- Reporter: nfrisby | Owner: nfrisby Type: task | Status: new Priority: normal | Milestone: 7.8.1 Component: | Version: 7.7 Compiler | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: #4941, #5302, #6087, #4962 None/Unknown | Test Case: | Blocking: | ----------------------------+---------------------------------------------- Description changed by nfrisby: Old description:

There are some tickets documenting runtime bugs that can be cleaned up by running the demand analyzer (followed by a simplifier run) a second time at the end of the pipeline: #4941, #5302, #6087. #6070 ? Others?

Here's the effects on nofib. Run time didn't seem to change as drastically. The "X/Y" column headers mean "library-flags/test-flags" given to GHC when compiling the respective bit.

{{{ Allocations

------------------------------------------------------------------------------- Program O2/O2 late-dmd+O2/O2 late-dmd+O2 /late-dmd+O2 ------------------------------------------------------------------------------- cryptarithm2 25078168 +0.0% +8.0% nucleic2 98331744 +0.0% +3.2%

cichelli 80310632 +0.0% -22.9% fasta 401159024 -9.1% -9.1% fulsom 321427240 +0.0% -2.6% k-nucleotide 4125102928 -0.0% -4.8% knights 2037984 +0.0% -3.7% mandel2 1041840 +0.0% -21.4% parstof 3103208 +0.0% -1.4% reverse-complem 155188304 -12.8% -12.8% simple 226412800 -0.0% -1.0% }}} All other changes less than 1% allocation. Note that it improves a couple tests significantly just via changes in the base libraries.

For cryptarithm2, (cf remarks in #4941) * 4% increase allocation is due to reboxing * 4% is due to dead closures, because the fix in #4962 isn't working for some reason.

For nucleic2, in var_most_distant_atom, an let-bound function is inlined after w/w, and hence grows numerous closures by a significant amount. I'm not sure where to lay the blame for this. Note however, that just making nucleic2's data types use strict !Float fields changes its allocation -72.4%, so maybe this "bad practice" corner case is a small issue.

The main remaining task beyond the attached patch is to repair the treatment of wrapper's strictness signatures in .hi files. Because the second demand analysis might change a these signatures, the current compaction mechanism that .hi uses results in ill-formed Core. For the attached patch, I've just disabled that .hi compaction mechanism, but this just needlessly bloats .hi files.

New description: There are some tickets documenting runtime bugs that can be cleaned up by running the demand analyzer (followed by a simplifier run) a second time at the end of the pipeline: #4941, #5302, #6087. #6070 ? Others? The -flate-dmd-anal flag has been committed to HEAD (cf comment:10 below). The remaining task is to determine if `-O2` should imply `-flate-dmd- anal`. It currently does not: late demand analysis is ''off'' by default. See LateDmd for more info. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7782#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler