Overhaul the Overhauled Pattern Match Checker

Overhaul the Overhauled Pattern Match Checker

* Changed the representation of Value Set Abstractions. Instead of
using a prefix tree, we now use a list of Value Vector Abstractions.
The set of constraints Delta for every Value Vector Abstraction is the
oracle state so that we solve everything only once.

* Instead of doing everything lazily, we prune at once (and in general
everything is much stricter). Hence, an example written with pattern
guards is checked in almost the same time as the equivalent with
pattern matching.

* Do not store the covered and the divergent sets at all. Since what we
only need is a yes/no (does this clause cover anything? Does it force
any thunk?) We just keep a boolean for each.

* Removed flags `-Wtoo-many-guards` and `-ffull-guard-reasoning`.
Replaced with `fmax-pmcheck-iterations=n`. Still debatable what should
the default `n` be.

* When a guard is for sure not going to contribute anything, we treat
it as such: The oracle is not called and cases `CGuard`, `UGuard` and
`DGuard` from the paper are not happening at all (the generation of a
fresh variable, the unfolding of the pattern list etc.). his combined
with the above seems to be enough to drop the memory increase for test
T783 down to 18.7%.

* Do not export function `dsPmWarn` (it is now called directly from
within `checkSingle` and `checkMatches`).

* Make `PmExprVar` hold a `Name` instead of an `Id`. The term oracle
does not handle type information so using `Id` was a waste of
time/space.

* Added testcases T11195, T11303b (data families) and T11374

The patch addresses at least the following:
Trac #11195, #11276, #11303, #11374, #11162

Test Plan: validate

Reviewers: goldfire, bgamari, hvr, austin

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1795

1 files changed, 2 insertions, 14 deletions

diff --git a/compiler/deSugar/Match.hs b/compiler/deSugar/Match.hs
index 0128488d62..be089e6788 100644
--- a/compiler/deSugar/Match.hs
+++ b/compiler/deSugar/Match.hs
@@ -694,21 +694,9 @@ matchWrapper ctxt mb_scr (MG { mg_alts = L _ matches
 
             when (isAnyPmCheckEnabled dflags (DsMatchContext ctxt locn)) $ do
 
-              -- Count the number of guards that can fail
-              guards <- computeNoGuards matches
-
-              let simplify = not (gopt Opt_FullGuardReasoning dflags)
-                              && (guards > maximum_failing_guards)
-
               -- See Note [Type and Term Equality Propagation]
               addTmCsDs (genCaseTmCs1 mb_scr new_vars) $
-                dsPmWarn dflags (DsMatchContext ctxt locn) $
-                  checkMatches simplify new_vars matches
-
-              when (not (gopt Opt_FullGuardReasoning dflags)
-                      && wopt Opt_WarnTooManyGuards dflags
-                      && guards > maximum_failing_guards)
-                   (warnManyGuards (DsMatchContext ctxt locn))
+                checkMatches dflags (DsMatchContext ctxt locn) new_vars matches
 
         ; result_expr <- handleWarnings $
                          matchEquations ctxt new_vars eqns_info rhs_ty
@@ -777,7 +765,7 @@ matchSinglePat (Var var) ctx pat ty match_result
        ; locn   <- getSrcSpanDs
        ; let pat' = getMaybeStrictPat dflags pat
        -- pattern match check warnings
-       ; dsPmWarn dflags (DsMatchContext ctx locn) (checkSingle var pat')
+       ; checkSingle dflags (DsMatchContext ctx locn) var pat'
 
        ; match [var] ty
                [EqnInfo { eqn_pats = [pat'], eqn_rhs  = match_result }] }