Overhaul the Overhauled Pattern Match Checker
authorGeorge Karachalias <george.karachalias@gmail.com>
Wed, 3 Feb 2016 18:06:45 +0000 (19:06 +0100)
committerBen Gamari <ben@smart-cactus.org>
Thu, 4 Feb 2016 09:27:36 +0000 (10:27 +0100)
commit28f951edfe50ea5182065144340061ec326781f5
tree0bb7ecd5b29518b0addca890ededb967f09273ca
parentdb121b2ec4596b99fed9781ec2d055f29e0d5b20
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
24 files changed:
compiler/deSugar/Check.hs
compiler/deSugar/DsMonad.hs
compiler/deSugar/Match.hs
compiler/deSugar/PmExpr.hs
compiler/deSugar/TmOracle.hs
compiler/ghci/RtClosureInspect.hs
compiler/main/DynFlags.hs
compiler/nativeGen/Dwarf/Constants.hs
compiler/typecheck/TcRnTypes.hs
compiler/types/OptCoercion.hs
docs/users_guide/8.0.1-notes.rst
docs/users_guide/bugs.rst
docs/users_guide/using-warnings.rst
libraries/base/Foreign/C/Error.hs
testsuite/tests/perf/compiler/all.T
testsuite/tests/pmcheck/should_compile/T11195.hs [new file with mode: 0644]
testsuite/tests/pmcheck/should_compile/T11303b.hs [new file with mode: 0644]
testsuite/tests/pmcheck/should_compile/T11374.hs [new file with mode: 0644]
testsuite/tests/pmcheck/should_compile/T2204.stderr
testsuite/tests/pmcheck/should_compile/T9951b.stderr
testsuite/tests/pmcheck/should_compile/all.T
testsuite/tests/pmcheck/should_compile/pmc001.stderr
testsuite/tests/pmcheck/should_compile/pmc007.stderr
utils/mkUserGuidePart/Options/Warnings.hs