| Commit message (Collapse) | Author | Age | Files | Lines |
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When desugaring large overloaded literals we now avoid
computing the `Rational` value. Instead prefering to
store the significant and exponent as given where
reasonable and possible.
See Note [FractionalLit representation] for details.
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This commit fixes 19 tests which were failing due to the use of
`consBag` / `snocBag`, which have been now replaced by `addMessage`.
This means that now GHC would output things in different order but
only for /diagnostics on the same line/, so this is just reflecting
that. The "normal" order of messages is still guaranteed.
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The `expect_broken` of `T14059b` expected outdated output.
But #14059 has long been fixed, so we this commit accepts the new output
and marks the test as unbroken.
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Consider `T18960`:
```hs
pattern P :: a -> a
pattern P x = x
{-# COMPLETE P :: () #-}
foo :: ()
foo = case () of
P _ -> ()
```
We know about the match variable of the case match that it is equal to `()`.
After the match on `P`, we still know it's equal to `()` (positive info), but
also that it can't be `P` (negative info). By the `COMPLETE` pragma, we know
that implies that the refinement type of the match variable is empty after the
`P` case.
But in the PmCheck solver, we assumed that "has positive info" means
"is not empty", thus assuming we could omit a costly inhabitation test. Which
is wrong, as we saw above.
A bit of a complication arises because the "has positive info" spared us
from doing a lot of inhabitation tests in `T17836b`. So we keep that
check, but give it a lower priority than the check for dirty variables
that requires us doing an inhabitation test.
Needless to say: This doesn't impact soundness of the checker at all,
it just implements a better trade-off between efficiency and precision.
Fixes #18960.
Metric Decrease:
T17836
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* -Wincomplete-uni-patterns
* -Wincomplete-record-updates
See https://gitlab.haskell.org/ghc/ghc/-/issues/15656
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This was inadvertently merged.
This reverts commit 6c2eb2232b39ff4720fda0a4a009fb6afbc9dcea.
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This implements the BoxedRep proposal, refacoring the `RuntimeRep`
hierarchy from:
```haskell
data RuntimeRep = LiftedPtrRep | UnliftedPtrRep | ...
```
to
```haskell
data RuntimeRep = BoxedRep Levity | ...
data Levity = Lifted | Unlifted
```
Closes #17526.
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In order to avoid confusion as in #18932, we display the type of the
match variables in the non-exhaustiveness warning, e.g.
```
T18932.hs:14:1: warning: [-Wincomplete-patterns]
Pattern match(es) are non-exhaustive
In an equation for ‘g’:
Patterns of type ‘T a’, ‘T a’, ‘T a’ not matched:
(MkT2 _) (MkT1 _) (MkT1 _)
(MkT2 _) (MkT1 _) (MkT2 _)
(MkT2 _) (MkT2 _) (MkT1 _)
(MkT2 _) (MkT2 _) (MkT2 _)
...
|
14 | g (MkT1 x) (MkT1 _) (MkT1 _) = x
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
It also allows us to omit the type signature on wildcard matches which
we previously showed in only some situations, particularly
`-XEmptyCase`.
Fixes #18932.
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Now `desugarLocalBind` (formerly `desugarLet`) reasons about
* `FunBind`s that
* Have no pattern matches (so which aren't functions)
* Have a singleton match group with a single GRHS
* (which may have guards)
* and looks through trivial post-typechecking `AbsBinds` in doing so
to pick up the introduced renamings.
And desugars to `PmLet` LYG-style guards. Since GRHSs are no longer
denoted simply by `NonEmpty PmGRHS`, but also need to carry a `[PmGrd]`
for the `PmLet`s from `LocalBind`s, I added `PmGRHSs` to capture that.
Since we call out to the desugarer more often, I found that there were
superfluous warnings emitted when desugaring e.g. case expressions.
Thus, I made sure that we deactivate any warnings in the LYG desugaring
steps by the new wrapper function `noCheckDs`.
There's a regression test in `T18626`. Fixes #18626.
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The expected test output was plain wrong.
It has been fixed for a long time.
Thus we can close #17218.
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The egregious performance hits are gone since !4050.
So we fix #18609.
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They have been fixed by !3959, I believe.
Fixes #18371.
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(#18708)
Fixes #18708.
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We used to produce inhabitants of a pattern-match refinement type Nabla
in the checker in at least two different and mostly redundant ways:
1. There was `provideEvidence` (now called
`generateInhabitingPatterns`) which is used by
`GHC.HsToCore.PmCheck` to produce non-exhaustive patterns, which
produces inhabitants of a Nabla as a sub-refinement type where all
match variables are instantiated.
2. There also was `ensure{,All}Inhabited` (now called
`inhabitationTest`) which worked slightly different, but was
whenever new type constraints or negative term constraints were
added. See below why `provideEvidence` and `ensureAllInhabited`
can't be the same function, the main reason being performance.
3. And last but not least there was the `nonVoid` test, which tested
that a given type was inhabited. We did use this for strict fields
and -XEmptyCase in the past.
The overlap of (3) with (2) was always a major pet peeve of mine. The
latter was quite efficient and proven to work for recursive data types,
etc, but could not handle negative constraints well (e.g. we often want
to know if a *refined* type is empty, such as `{ x:[a] | x /= [] }`).
Lower Your Guards suggested that we could get by with just one, by
replacing both functions with `inhabitationTest` in this patch.
That was only possible by implementing the structure of φ constraints
as in the paper, namely the semantics of φ constructor constraints.
This has a number of benefits:
a. Proper handling of unlifted types and strict fields, fixing #18249,
without any code duplication between
`GHC.HsToCore.PmCheck.Oracle.instCon` (was `mkOneConFull`) and
`GHC.HsToCore.PmCheck.checkGrd`.
b. `instCon` can perform the `nonVoid` test (3) simply by emitting
unliftedness constraints for strict fields.
c. `nonVoid` (3) is thus simply expressed by a call to
`inhabitationTest`.
d. Similarly, `ensureAllInhabited` (2), which we called after adding
type info, now can similarly be expressed as the fuel-based
`inhabitationTest`.
See the new `Note [Why inhabitationTest doesn't call generateInhabitingPatterns]`
why we still have tests (1) and (2).
Fixes #18249 and brings nice metric decreases for `T17836` (-76%) and
`T17836b` (-46%), as well as `T18478` (-8%) at the cost of a few very
minor regressions (< +2%), potentially due to the fact that
`generateInhabitingPatterns` does more work to suggest the minimal
COMPLETE set.
Metric Decrease:
T17836
T17836b
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By taking and returning an `InertSet`.
Every new `TcS` session can then pick up where a prior session left with
`setTcSInerts`.
Since we don't want to unflatten the Givens (and because it leads to
infinite loops, see !3971), we introduced a new variant of `runTcS`,
`runTcSInerts`, that takes and returns the `InertSet` and makes
sure not to unflatten the Givens after running the `TcS` action.
Fixes #18645 and #17836.
Metric Decrease:
T17977
T18478
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By not attaching COMPLETE pragmas with a particular TyCon and instead
assume that every COMPLETE pragma is applicable everywhere, we can
drastically simplify the logic that tries to initialise available
COMPLETE sets of a variable during the pattern-match checking process,
as well as fixing a few bugs.
Of course, we have to make sure not to report any of the
ill-typed/unrelated COMPLETE sets, which came up in a few regression
tests.
In doing so, we fix #17207, #18277 and #14422.
There was a metric decrease in #18478 by ~20%.
Metric Decrease:
T18478
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In #18341, we discovered an incorrect digression from Lower Your Guards.
This MR changes what's necessary to support properly fixing #18341.
In particular, bottomness constraints are now properly tracked in the
oracle/inhabitation testing, as an additional field
`vi_bot :: Maybe Bool` in `VarInfo`. That in turn allows us to
model newtypes as advertised in the Appendix of LYG and fix #17725.
Proper handling of ⊥ also fixes #17977 (once again) and fixes #18670.
For some reason I couldn't follow, this also fixes #18273.
I also added a couple of regression tests that were missing. Most of
them were already fixed before.
In summary, this patch fixes #18341, #17725, #18273, #17977 and #18670.
Metric Decrease:
T12227
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source syntax (#18565)
Previously, we desugared and coverage checked plain guard trees as
described in Lower Your Guards. That caused (in !3849) quite a bit of
pain when we need to partially recover tree structure of the input
syntax to return covered sets for long-distance information, for
example.
In this refactor, I introduced a guard tree variant for each relevant
source syntax component of a pattern-match (mainly match groups, match,
GRHS, empty case, pattern binding). I made sure to share as much
coverage checking code as possible, so that the syntax-specific checking
functions are just wrappers around the more substantial checking
functions for the LYG primitives (`checkSequence`, `checkGrds`).
The refactoring payed off in clearer code and elimination of all panics
related to assumed guard tree structure and thus fixes #18565.
I also took the liberty to rename and re-arrange the order of functions
and comments in the module, deleted some dead and irrelevant Notes,
wrote some new ones and gave an overview module haddock.
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We didn't consider the RHS of a pattern-binding before, which led to
surprising warnings listed in #18572.
As can be seen from the regression test T18572, we get the expected
output now.
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Add new flag '-Wredundant-bang-patterns' that enables checks for "dead" bangs.
Dead bangs are the ones that under no circumstances can force a thunk that
wasn't already forced. Dead bangs are a form of redundant bangs. The new check
is performed in Pattern-Match Coverage Checker along with other checks (namely,
redundant and inaccessible RHSs). Given
f :: Bool -> Int
f True = 1
f !x = 2
we can detect dead bang patterns by checking whether @x ~ ⊥@ is satisfiable
where the PmBang appears in 'checkGrdTree'. If not, then clearly the bang is
dead. Such a dead bang is then indicated in the annotated pattern-match tree by
a 'RedundantSrcBang' wrapping. In 'redundantAndInaccessibles', we collect
all dead bangs to warn about.
Note that we don't want to warn for a dead bang that appears on a redundant
clause. That is because in that case, we recommend to delete the clause wholly,
including its leading pattern match.
Dead bang patterns are redundant. But there are bang patterns which are
redundant that aren't dead, for example
f !() = 0
the bang still forces the match variable, before we attempt to match on (). But
it is redundant with the forcing done by the () match. We currently don't
detect redundant bangs that aren't dead.
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Where bindings can see evidence from the pattern match of the `GRHSs`
they belong to, but not from anything in any of the guards (which belong
to one of possibly many RHSs).
Before this patch, we did *not* consider said evidence, causing #18533,
where the lack of considering type information from a case pattern match
leads to failure to resolve the vanilla COMPLETE set of a data type.
Making available that information required a medium amount of
refactoring so that `checkMatches` can return a
`[(Deltas, NonEmpty Deltas)]`; one `(Deltas, NonEmpty Deltas)` for each
`GRHSs` of the match group. The first component of the pair is the
covered set of the pattern, the second component is one covered set per
RHS.
Fixes #18533.
Regression test case: T18533
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Change `Located X` usage to `XRec pass X`
This increases the scope of the LPat experiment to almost all of GHC.
Introduce UnXRec and MapXRec classes
Fixes #17587 and #18408
Updates haddock submodule
Co-authored-by: Philipp Krüger <philipp.krueger1@gmail.com>
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!3392 backported !2993 to GHC 8.10.2 which most probably is responsible
for fixing #18478, which triggered a pattern match checker performance
regression in GHC 8.10.1 as first observed in #17977.
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`HsWrapper`s introduce evidence bindings through `WpEvLam` which the
pattern-match coverage checker should be made aware of.
Failing to do so caused #18049, where the resulting impreciseness of
imcompleteness warnings seemingly contradicted with
`-Winaccessible-code`.
The solution is simple: Collect all the evidence binders of an
`HsWrapper` and add it to the ambient `Deltas` before desugaring
the wrapped expression.
But that means we pick up many more evidence bindings, even when they
wrap around code without a single pattern match to check! That regressed
`T3064` by over 300%, so now we are adding long-distance info lazily
through judicious use of `unsafeInterleaveIO`.
Fixes #18049.
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Update Haddock submodule
Metric Increase:
haddock.compiler
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Update Haddock submodule
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In #17977, we ran into the reduction depth limit of the typechecker.
That was only a symptom of a much broader issue: The recursion depth
of the coverage checker for trying to instantiate strict fields in the
`nonVoid` test was far too high (100, the `defaultMaxTcBound`).
As a result, we were performing quite poorly on `T17977`.
Short of a proper termination analysis to prove emptyness of a type,
we just arbitrarily default to a much lower recursion limit of 3.
Fixes #17977.
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Update Haddock submodule
Metric Increase:
haddock.compiler
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Update submodule: haddock
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Consider
```hs
data T = A | B | C
f :: T -> Int
f A = 1
f x = case x of
A -> 2
B -> 3
C -> 4
```
Clearly, the RHS returning 2 is redundant. But we don't currently see
that, because our approximation to the covered set of the inner case
expression just picks up the positive information from surrounding
pattern matches. It lacks the context sensivity that `x` can't be `A`
anymore!
Therefore, we adopt the conceptually and practically superior approach
of reusing the covered set of a particular GRHS from an outer pattern
match. In this case, we begin checking the `case` expression with the
covered set of `f`s second clause, which encodes the information that
`x` can't be `A` anymore. After this MR, we will successfully warn about
the RHS returning 2 being redundant.
Perhaps surprisingly, this was a great simplification to the code of
both the coverage checker and the desugarer.
Found a redundant case alternative in `unix` submodule, so we have to
bump it with a fix.
Metric Decrease:
T12227
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(Commit message written by Omer, most of the code is written by Simon
and Richard)
See Note [Implementing unsafeCoerce] for how unsafe equality proofs and
the new unsafeCoerce# are implemented.
New notes added:
- [Checking for levity polymorphism] in CoreLint.hs
- [Implementing unsafeCoerce] in base/Unsafe/Coerce.hs
- [Patching magic definitions] in Desugar.hs
- [Wiring in unsafeCoerce#] in Desugar.hs
Only breaking change in this patch is unsafeCoerce# is not exported from
GHC.Exts, instead of GHC.Prim.
Fixes #17443
Fixes #16893
NoFib
-----
--------------------------------------------------------------------------------
Program Size Allocs Instrs Reads Writes
--------------------------------------------------------------------------------
CS -0.1% 0.0% -0.0% -0.0% -0.0%
CSD -0.1% 0.0% -0.0% -0.0% -0.0%
FS -0.1% 0.0% -0.0% -0.0% -0.0%
S -0.1% 0.0% -0.0% -0.0% -0.0%
VS -0.1% 0.0% -0.0% -0.0% -0.0%
VSD -0.1% 0.0% -0.0% -0.0% -0.1%
VSM -0.1% 0.0% -0.0% -0.0% -0.0%
anna -0.0% 0.0% -0.0% -0.0% -0.0%
ansi -0.1% 0.0% -0.0% -0.0% -0.0%
atom -0.1% 0.0% -0.0% -0.0% -0.0%
awards -0.1% 0.0% -0.0% -0.0% -0.0%
banner -0.1% 0.0% -0.0% -0.0% -0.0%
bernouilli -0.1% 0.0% -0.0% -0.0% -0.0%
binary-trees -0.1% 0.0% -0.0% -0.0% -0.0%
boyer -0.1% 0.0% -0.0% -0.0% -0.0%
boyer2 -0.1% 0.0% -0.0% -0.0% -0.0%
bspt -0.1% 0.0% -0.0% -0.0% -0.0%
cacheprof -0.1% 0.0% -0.0% -0.0% -0.0%
calendar -0.1% 0.0% -0.0% -0.0% -0.0%
cichelli -0.1% 0.0% -0.0% -0.0% -0.0%
circsim -0.1% 0.0% -0.0% -0.0% -0.0%
clausify -0.1% 0.0% -0.0% -0.0% -0.0%
comp_lab_zift -0.1% 0.0% -0.0% -0.0% -0.0%
compress -0.1% 0.0% -0.0% -0.0% -0.0%
compress2 -0.1% 0.0% -0.0% -0.0% -0.0%
constraints -0.1% 0.0% -0.0% -0.0% -0.0%
cryptarithm1 -0.1% 0.0% -0.0% -0.0% -0.0%
cryptarithm2 -0.1% 0.0% -0.0% -0.0% -0.0%
cse -0.1% 0.0% -0.0% -0.0% -0.0%
digits-of-e1 -0.1% 0.0% -0.0% -0.0% -0.0%
digits-of-e2 -0.1% 0.0% -0.0% -0.0% -0.0%
dom-lt -0.1% 0.0% -0.0% -0.0% -0.0%
eliza -0.1% 0.0% -0.0% -0.0% -0.0%
event -0.1% 0.0% -0.0% -0.0% -0.0%
exact-reals -0.1% 0.0% -0.0% -0.0% -0.0%
exp3_8 -0.1% 0.0% -0.0% -0.0% -0.0%
expert -0.1% 0.0% -0.0% -0.0% -0.0%
fannkuch-redux -0.1% 0.0% -0.0% -0.0% -0.0%
fasta -0.1% 0.0% -0.5% -0.3% -0.4%
fem -0.1% 0.0% -0.0% -0.0% -0.0%
fft -0.1% 0.0% -0.0% -0.0% -0.0%
fft2 -0.1% 0.0% -0.0% -0.0% -0.0%
fibheaps -0.1% 0.0% -0.0% -0.0% -0.0%
fish -0.1% 0.0% -0.0% -0.0% -0.0%
fluid -0.1% 0.0% -0.0% -0.0% -0.0%
fulsom -0.1% 0.0% +0.0% +0.0% +0.0%
gamteb -0.1% 0.0% -0.0% -0.0% -0.0%
gcd -0.1% 0.0% -0.0% -0.0% -0.0%
gen_regexps -0.1% 0.0% -0.0% -0.0% -0.0%
genfft -0.1% 0.0% -0.0% -0.0% -0.0%
gg -0.1% 0.0% -0.0% -0.0% -0.0%
grep -0.1% 0.0% -0.0% -0.0% -0.0%
hidden -0.1% 0.0% -0.0% -0.0% -0.0%
hpg -0.1% 0.0% -0.0% -0.0% -0.0%
ida -0.1% 0.0% -0.0% -0.0% -0.0%
infer -0.1% 0.0% -0.0% -0.0% -0.0%
integer -0.1% 0.0% -0.0% -0.0% -0.0%
integrate -0.1% 0.0% -0.0% -0.0% -0.0%
k-nucleotide -0.1% 0.0% -0.0% -0.0% -0.0%
kahan -0.1% 0.0% -0.0% -0.0% -0.0%
knights -0.1% 0.0% -0.0% -0.0% -0.0%
lambda -0.1% 0.0% -0.0% -0.0% -0.0%
last-piece -0.1% 0.0% -0.0% -0.0% -0.0%
lcss -0.1% 0.0% -0.0% -0.0% -0.0%
life -0.1% 0.0% -0.0% -0.0% -0.0%
lift -0.1% 0.0% -0.0% -0.0% -0.0%
linear -0.1% 0.0% -0.0% -0.0% -0.0%
listcompr -0.1% 0.0% -0.0% -0.0% -0.0%
listcopy -0.1% 0.0% -0.0% -0.0% -0.0%
maillist -0.1% 0.0% -0.0% -0.0% -0.0%
mandel -0.1% 0.0% -0.0% -0.0% -0.0%
mandel2 -0.1% 0.0% -0.0% -0.0% -0.0%
mate -0.1% 0.0% -0.0% -0.0% -0.0%
minimax -0.1% 0.0% -0.0% -0.0% -0.0%
mkhprog -0.1% 0.0% -0.0% -0.0% -0.0%
multiplier -0.1% 0.0% -0.0% -0.0% -0.0%
n-body -0.1% 0.0% -0.0% -0.0% -0.0%
nucleic2 -0.1% 0.0% -0.0% -0.0% -0.0%
para -0.1% 0.0% -0.0% -0.0% -0.0%
paraffins -0.1% 0.0% -0.0% -0.0% -0.0%
parser -0.1% 0.0% -0.0% -0.0% -0.0%
parstof -0.1% 0.0% -0.0% -0.0% -0.0%
pic -0.1% 0.0% -0.0% -0.0% -0.0%
pidigits -0.1% 0.0% -0.0% -0.0% -0.0%
power -0.1% 0.0% -0.0% -0.0% -0.0%
pretty -0.1% 0.0% -0.1% -0.1% -0.1%
primes -0.1% 0.0% -0.0% -0.0% -0.0%
primetest -0.1% 0.0% -0.0% -0.0% -0.0%
prolog -0.1% 0.0% -0.0% -0.0% -0.0%
puzzle -0.1% 0.0% -0.0% -0.0% -0.0%
queens -0.1% 0.0% -0.0% -0.0% -0.0%
reptile -0.1% 0.0% -0.0% -0.0% -0.0%
reverse-complem -0.1% 0.0% -0.0% -0.0% -0.0%
rewrite -0.1% 0.0% -0.0% -0.0% -0.0%
rfib -0.1% 0.0% -0.0% -0.0% -0.0%
rsa -0.1% 0.0% -0.0% -0.0% -0.0%
scc -0.1% 0.0% -0.1% -0.1% -0.1%
sched -0.1% 0.0% -0.0% -0.0% -0.0%
scs -0.1% 0.0% -0.0% -0.0% -0.0%
simple -0.1% 0.0% -0.0% -0.0% -0.0%
solid -0.1% 0.0% -0.0% -0.0% -0.0%
sorting -0.1% 0.0% -0.0% -0.0% -0.0%
spectral-norm -0.1% 0.0% -0.0% -0.0% -0.0%
sphere -0.1% 0.0% -0.0% -0.0% -0.0%
symalg -0.1% 0.0% -0.0% -0.0% -0.0%
tak -0.1% 0.0% -0.0% -0.0% -0.0%
transform -0.1% 0.0% -0.0% -0.0% -0.0%
treejoin -0.1% 0.0% -0.0% -0.0% -0.0%
typecheck -0.1% 0.0% -0.0% -0.0% -0.0%
veritas -0.0% 0.0% -0.0% -0.0% -0.0%
wang -0.1% 0.0% -0.0% -0.0% -0.0%
wave4main -0.1% 0.0% -0.0% -0.0% -0.0%
wheel-sieve1 -0.1% 0.0% -0.0% -0.0% -0.0%
wheel-sieve2 -0.1% 0.0% -0.0% -0.0% -0.0%
x2n1 -0.1% 0.0% -0.0% -0.0% -0.0%
--------------------------------------------------------------------------------
Min -0.1% 0.0% -0.5% -0.3% -0.4%
Max -0.0% 0.0% +0.0% +0.0% +0.0%
Geometric Mean -0.1% -0.0% -0.0% -0.0% -0.0%
Test changes
------------
- break006 is marked as broken, see #17833
- The compiler allocates less when building T14683 (an unsafeCoerce#-
heavy happy-generated code) on 64-platforms. Allocates more on 32-bit
platforms.
- Rest of the increases are tiny amounts (still enough to pass the
threshold) in micro-benchmarks. I briefly looked at each one in a
profiling build: most of the increased allocations seem to be because
of random changes in the generated code.
Metric Decrease:
T14683
Metric Increase:
T12150
T12234
T12425
T13035
T14683
T5837
T6048
Co-Authored-By: Richard Eisenberg <rae@cs.brynmawr.edu>
Co-Authored-By: Ömer Sinan Ağacan <omeragacan@gmail.com>
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For record updates where the `record_expr` is a variable, as in #17783:
```hs
data PartialRec = No
| Yes { a :: Int, b :: Bool }
update No = No
update r@(Yes {}) = r { b = False }
```
We should make use of long distance info in
`-Wincomplete-record-updates` checking. But the call to `matchWrapper`
in the `RecUpd` case didn't specify a scrutinee expression, which would
correspond to the `record_expr` `r` here. That is fixed now.
Fixes #17783.
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In #17703 (a follow-up of !2192), we established that contrary to my
belief, type constraints arising from existentials in code like
```hs
data Ex where Ex :: a -> Ex
f _ | let x = Ex @Int 15 = case x of Ex -> ...
```
are in fact useful.
This commit makes a number of refactorings and improvements to comments,
but fundamentally changes `addCoreCt.core_expr` to record the type
constraint `a ~ Int` in addition to `x ~ Ex @a y` and `y ~ 15`.
Fixes #17703.
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We used to check `GrdVec`s arising from multiple clauses and guards in
isolation. That resulted in a split between `pmCheck` and
`pmCheckGuards`, the implementations of which were similar, but subtly
different in detail. Also the throttling mechanism described in
`Note [Countering exponential blowup]` ultimately got quite complicated
because it had to cater for both checking functions.
This patch realises that pattern match checking doesn't just consider
single guarded RHSs, but that it's always a whole set of clauses, each
of which can have multiple guarded RHSs in turn. We do so by
translating a list of `Match`es to a `GrdTree`:
```haskell
data GrdTree
= Rhs !RhsInfo
| Guard !PmGrd !GrdTree -- captures lef-to-right match semantics
| Sequence !GrdTree !GrdTree -- captures top-to-bottom match semantics
| Empty -- For -XEmptyCase, neutral element of Sequence
```
Then we have a function `checkGrdTree` that matches a given `GrdTree`
against an incoming set of values, represented by `Deltas`:
```haskell
checkGrdTree :: GrdTree -> Deltas -> CheckResult
...
```
Throttling is isolated to the `Sequence` case and becomes as easy as one
would expect: When the union of uncovered values becomes too big, just
return the original incoming `Deltas` instead (which is always a
superset of the union, thus a sound approximation).
The returned `CheckResult` contains two things:
1. The set of values that were not covered by any of the clauses, for
exhaustivity warnings.
2. The `AnnotatedTree` that enriches the syntactic structure of the
input program with divergence and inaccessibility information.
This is `AnnotatedTree`:
```haskell
data AnnotatedTree
= AccessibleRhs !RhsInfo
| InaccessibleRhs !RhsInfo
| MayDiverge !AnnotatedTree
| SequenceAnn !AnnotatedTree !AnnotatedTree
| EmptyAnn
```
Crucially, `MayDiverge` asserts that the tree may force diverging
values, so not all of its wrapped clauses can be redundant.
While the set of uncovered values can be used to generate the missing
equations for warning messages, redundant and proper inaccessible
equations can be extracted from `AnnotatedTree` by
`redundantAndInaccessibleRhss`.
For this to work properly, the interface to the Oracle had to change.
There's only `addPmCts` now, which takes a bag of `PmCt`s. There's a
whole bunch of `PmCt` variants to replace the different oracle functions
from before.
The new `AnnotatedTree` structure allows for more accurate warning
reporting (as evidenced by a number of changes spread throughout GHC's
code base), thus we fix #17465.
Fixes #17646 on the go.
Metric Decrease:
T11822
T9233
PmSeriesS
haddock.compiler
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Metric Decrease:
haddock.compiler
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We can handle non-void constraints since !1733, so we can now express
the strictness of `-XEmptyCase` just by adding a non-void constraint
to the initial Uncovered set.
For `case x of {}` we thus check that the Uncovered set `{ x | x /~ ⊥ }`
is non-empty. This is conceptually simpler than the plan outlined in
#17376, because it talks to the oracle directly.
In order for this patch to pass the testsuite, I had to fix handling of
newtypes in the pattern-match checker (#17248).
Since we use a different code path (well, the main code path) for
`-XEmptyCase` now, we apparently also handle #13717 correctly.
There's also some dead code that we can get rid off now.
`provideEvidence` has been updated to provide output more in line with
the old logic, which used `inhabitationCandidates` under the hood.
A consequence of the shift away from the `UncoveredPatterns` type is
that we don't report reduced type families for empty case matches,
because the pretty printer is pure and only knows the match variable's
type.
Fixes #13717, #17248, #17386
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Simon realised that the simple language composed of let bindings, bang
patterns and flat constructor patterns is enough to capture the
semantics of the source pattern language that are important for
pattern-match checking. Well, given that the Oracle is smart enough to
connect the dots in this less informationally dense form, which it is
now.
So we transform `translatePat` to return a list of `PmGrd`s relative to
an incoming match variable. `pmCheck` then trivially translates each of
the `PmGrd`s into constraints that the oracle understands.
Since we pass in the match variable, we incidentally fix #15884
(coverage checks for view patterns) through an interaction with !1746.
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The vanilla COMPLETE set is attached to the representation TyCon of a
data family instance, whereas the user-defined COMPLETE sets are
attached to the parent data family TyCon itself.
Previously, we weren't trying particularly hard to get back to the
representation TyCon to the parent data family TyCon, resulting in bugs
like #17207. Now we should do much better.
Fixes the original issue in #17207, but I found another related bug that
isn't so easy to fix.
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By introducing a `CoreMap Id` to the term oracle, we can represent
syntactically equivalent expressions by the same `Id`. Combine that with
`CoreOpt.simpleCoreExpr` and it might even catch non-trivial semantic
equalities.
Unfortunately due to scoping issues, this will not solve #17208 for
view patterns yet.
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In his paper "Warnings for Pattern Matching", Luke Maranget describes
three series in his appendix for which GHC's pattern match checker
scaled very badly. We mostly avoid this now with !1752. This commit adds
regression tests for each of the series.
Fixes #17264.
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Adds regression tests for tickets #17207, #17208, #17215, #17216,
#17218, #17219, #17248
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`pmcheck` used to call `refineToAltCon` which would refine the knowledge
we had about a variable by equating it to a `ConLike` application.
Since we weren't particularly smart about this in the Check module, we
simply freshened the constructors existential and term binders utimately
through a call to `mkOneConFull`.
But that instantiation is unnecessary for when we match against a
concrete pattern! The pattern will already have fresh binders and field
types. So we don't call `refineToAltCon` from `Check` anymore.
Subsequently, we can simplify a couple of call sites and functions in
`PmOracle`. Also implementing `computeCovered` becomes viable and we
don't have to live with the hack that was `addVarPatVecCt` anymore.
A side-effect of not indirectly calling `mkOneConFull` anymore is that
we don't generate the proper strict argument field constraints anymore.
Instead we now desugar ConPatOuts as if they had bangs on their strict
fields. This implies that `PmVar` now carries a `HsImplBang` that we
need to respect by a (somewhat ephemeral) non-void check. We fix #17234
in doing so.
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Basically do what we currently only do for -XEmptyCase in other cases
where adding the type signature won't distract from pattern
matches in other positions.
We use the precedence to guide us, equating "need to parenthesise" with
"too much noise".
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Introduces a new flag `-fmax-pmcheck-deltas` to achieve that. Deprecates
the old `-fmax-pmcheck-iter` mechanism in favor of this new flag.
From the user's guide:
Pattern match checking can be exponential in some cases. This limit makes sure
we scale polynomially in the number of patterns, by forgetting refined
information gained from a partially successful match. For example, when
matching `x` against `Just 4`, we split each incoming matching model into two
sub-models: One where `x` is not `Nothing` and one where `x` is `Just y` but
`y` is not `4`. When the number of incoming models exceeds the limit, we
continue checking the next clause with the original, unrefined model.
This also retires the incredibly hard to understand "maximum number of
refinements" mechanism, because the current mechanism is more general
and should catch the same exponential cases like PrelRules at the same
time.
-------------------------
Metric Decrease:
T11822
-------------------------
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The pattern match oracle can now cope with the abundance of information
that ViewPatterns, NPlusKPats, overloaded lists, etc. provide.
No need to have PmFake anymore!
Also got rid of a spurious call to `allCompleteMatches`, which we used to call
*for every constructor* match. Naturally this blows up quadratically for
programs like `ManyAlternatives`.
-------------------------
Metric Decrease:
ManyAlternatives
Metric Increase:
T11822
-------------------------
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Add GHC.Hs module hierarchy replacing hsSyn.
Metric Increase:
haddock.compiler
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