Less Tc inside simplCore (Phase 1 for #14391)

Authored by ulysses4ever on May 15 2018, 5:07 PM.

Description

Less Tc inside simplCore (Phase 1 for Trac #14391)

Simplifier depends on typechecker in two points: thNameToGhcName
(lookupThName_maybe, in particular) and lookupGlobal. We want to
cut the ties in two steps.

  1. (Presented in this commit), reimplement both functions in a way that

doesn't use typechecker.

  1. (Should follow), do code moving: a) lookupGlobal should go in some

typechecker-free place; b) thNameToGhcName should leave simplifier,
because it is not used there at all (probably, it should be placed
somewhere where GhcPlugins can see it -- this is suggested by Joachim
on Trac).

Details

We redesigned lookup interface a bit so that it exposes some
IO-equivalents of Tc-features in use.

First, CoreMonad.hs still calls lookupGlobal which is no longer
bound to the typechecker monad, but still resides in TcEnv.hs — it
should be moved out of Tc-land at some point (“Phase 2”) in the
future in order to achieve its part of the Trac #14391's goal.

Second, lookupThName_maybe is eliminated from CoreMonad.hs
completely; this already achieves its part of the goal of Trac #14391. Its
client, though, thNameToGhcName, is better to be moved in the future
also, for it is not used in the CoreMonad.hs (or anywhere else)
anyway. Joachim suggested “any module reexported by GhcPlugins (or
maybe even that module itself)”.

As a side goal, we removed initTcForLookup which was instrumental for
the past version of lookupGlobal. This, in turn, called for pushing
some more parts of the lookup interface from the Tc-monad to IO,
most notably, adding IO-version of lookupOrig and pushing
dataConInfoPtrToName to IO. The lookupOrig part, in turn,
triggered a slight redesign of name cache updating interface: we now
have both, updNameCacheIO and updNameCacheTc, both accepting mod
and occ to force them inside, instead of more error-prone outside
before. But all these hardly have to do anything with Trac #14391, mere
refactoring.

Reviewers: simonpj, nomeata, bgamari, hvr

Reviewed By: simonpj, bgamari

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: Trac #14391

Differential Revision: https://phabricator.haskell.org/D4503