[commit: ghc] master: Refactor the Mighty Simplifier (33452df)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/33452dfc6cf891b59d63fa9fe138b18cbce4df81/ghc

>---------------------------------------------------------------

commit 33452dfc6cf891b59d63fa9fe138b18cbce4df81
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Aug 25 09:22:03 2017 +0100

    Refactor the Mighty Simplifier
    
    Triggered by #12150, and the knock-on effects of join points, I did a
    major refactoring of the Simplifier.  This is a big patch that change
    a lot of Simplify.hs: I did a lot of other re-organisation.
    
    The main event
    ~~~~~~~~~~~~~~
    Since the dawn of time we have had
      simplExpr :: SimplEnv -> InExpr -> SimplCont
                -> SimplM (SimplEnv, OutExpr)
    
    What's that SimplEnv in the result?  When simplifying an expression the
    simplifier add floated let-bindings to the SimplEnv, extending the
    in-scope set appropriately, and hence needs to resturn the SimplEnv at
    the end.  The mode, flags, substitution in the returned SimplEnv were
    all irrelevant: it was just the floating bindings.
    
    It's strange to accumulate part of the /result/ in the /environment/
    argument!  And indeed its leads to all manner of mysterious calls to
    zapFloats and transferring of floats from one SimplEnv to another.
    It got worse with join points, so I finally bit the bullet and refactored.
    Now we have
      simplExpr :: SimplEnv -> InExpr -> SimplCont
                -> SimplM (SimplFloats, OutExpr)
      -- See Note [The big picture]
    and the SimplEnv no longer has floats in it.  The code is no shorter,
    but it /is/ easier to understand.
    
    Main changes
    
    * Remove seLetFloats field from SimplEnv
    
    * Define new data type SimplFloats, and functions over it
    
    * Change the types of simplExpr, simplBind, and their many variants,
      to follow the above plan
    
    Bottoming bindings
    ~~~~~~~~~~~~~~~~~~
    I made one other significant change in SimplUtils (not just refactoring),
    related to Trac #12150 comment:16.  Given
      x = <rhs>
    where <rhs> turns out to be a bottoming expression, propagate that
    information to x's IdInfo immediately.  That's always good, because
    it makes x be inlined less (we don't inline bottoming things), and
    it allows (case x of ...) to drop the dead alterantives immediately.
    Moreover, we are doing the analysis anyway, in tryEtaExpandRhs, which
    calls CoreArity.findRhsArity, which already does simple bottom analysis.
    So we are generating the information; all we need do is to atach the
    bottoming info to the IdInfo.
    
    See Note [Bottoming bindings]
    
    Smaller refactoring
    ~~~~~~~~~~~~~~~~~~~
    * Rename SimplifierMode to SimplMode
    * Put DynFlags as a new field in SimplMode, to make fewer
      monadic calls to getDynFlags.
    * Move the code in addPolyBind into abstractFloats
    * Move the "don't eta-expand join points" into tryEtaExpandRhs


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33452dfc6cf891b59d63fa9fe138b18cbce4df81
 compiler/coreSyn/CoreArity.hs                      |   59 +-
 compiler/simplCore/CoreMonad.hs                    |   10 +-
 compiler/simplCore/SimplCore.hs                    |    9 +-
 compiler/simplCore/SimplEnv.hs                     |  316 ++--
 compiler/simplCore/SimplUtils.hs                   |  203 ++-
 compiler/simplCore/Simplify.hs                     | 1719 +++++++++-----------
 testsuite/tests/perf/compiler/T12150.hs            |  103 ++
 testsuite/tests/perf/compiler/all.T                |   10 +
 .../tests/simplCore/should_compile/T3234.stderr    |    4 +-
 .../tests/simplCore/should_compile/rule2.stderr    |    4 +-
 10 files changed, 1273 insertions(+), 1164 deletions(-)

Diff suppressed because of size. To see it, use:

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 33452dfc6cf891b59d63fa9fe138b18cbce4df81