Add integer-exact checks for inequalities being separate and redundant in LexSimplex.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122921
LexSimplex cannot be made to support symbols for symbolic lexmin; this requires
a second class. In preparation for upstreaming support for symbolic lexmin,
keep the part of LexSimplex that are specific to non-symbolic lexmin in LexSimplex
and move the parts that are required to a common class LexSimplexBase for both to
inherit from.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122828
This reverts commit 5630143af33f7e6e0dabdf38982cc9800140bb75. The
implementation in this commit was incorrect. Also, handling this representation
of equalities in the upcoming support for symbolic lexicographic minimization
makes that patch much more complex. It will be easier to review that without
this representaiton and then reintroduce the fixed column representation
later, hence the revert rather than a bug fix.
In LexSimplex, instead of adding equalities as a pair of inequalities,
add them as a single row, move them into the basis, and keep them there.
There will always be a valid basis involving all non-redundant equalities. Such
equalities will then be ignored in some other operations, such as when looking
for pivot columns. This speeds them up a little bit.
More importantly, this is an important precursor patch to adding support for
symbolic integer lexmin, as this heuristic can sometimes make a big difference there.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122165
This simplifies many places where we just want to do something in a "transient context"
and return some value.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122172
This is a convenience function for adding new divisions to the Simplex given the numerator and denominator.
This will be needed for symbolic integer lexmin support.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122159
Previously, an UndoLogEntry was added by addRow but not by addZeroRow. So
calling directly into addZeroRow, as LexSimplex::addCut does, was not an
undoable operation. In the current usage of addCut this could never
lead to an incorrect result, and addZeroRow is protected, so it is not
currently possible to add a regression test for this. This bug needs to be
fixed for the symbolic integer lexmin algorithm.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D122162
This patch moves all functionality from IntegerPolyhedron to IntegerRelation.
IntegerPolyhedron is now implemented as a relation with no domain. All existing
functionality is extended to work on relations.
This patch does not affect external users like FlatAffineConstraints as they
can still continue to use IntegerPolyhedron abstraction.
This patch is part of a series of patches to support relations in Presburger
library.
Reviewed By: arjunp
Differential Revision: https://reviews.llvm.org/D120652
This patch moves the Presburger library to a new `presburger` namespace.
This allows to shorten some names, helps to avoid polluting the mlir namespace,
and also provides some structure.
Reviewed By: arjunp
Differential Revision: https://reviews.llvm.org/D120505
This patch adds typing of inequalities to the simplex. This is a cental part of the coalesce algorithm and will be heavily used in later coalesce patches. Currently, only the three most basic types are supported with more to be introduced when they are needed.
Reviewed By: arjunp
Differential Revision: https://reviews.llvm.org/D119925
This allows to differentiate between the cases where the optimum does not
exist due to being unbounded and due to the polytope being empty.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D120127
This patch introduces a class LexSimplex that can currently be used to find the
lexicographically minimal rational point in an IntegerPolyhedron. This is a
series of patches leading to computing the lexicographically minimal integer
lattice point as well parametric lexicographic minimization.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D117437
Initialize some variables to zero to avoid a warning about them possibly being
used uninitialized. In actuality, they will never be used before initialization.
This patch replaces usage of FlatAffineConstraints in Simplex with
IntegerPolyhedron. This removes dependency of Simplex on FlatAffineConstraints
and puts it on IntegerPolyhedron, which is part of Presburger library.
Reviewed By: arjunp
Differential Revision: https://reviews.llvm.org/D116287
This is a purely mechanical patch moving some functionality out from the
`Simplex` class out into a `SimplexBase` class. This pavees the way for
a future patch adding support for lexicographic optimization with a class
`LexSimplex`, which will inherit from `SimplexBase`. Inheriting directly
from `Simplex` would bring many additional functions that would not work in
`LexSimplex` because it operates slighty differently from `Simplex`. So We
split out only the basic functionality it needs to inherit into `SimplexBase`.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D115831
Previously, the LogicalResult return value of restoreRow was being ignored in
places where it was expected to always be success. Instead, check the result
and go to an `llvm_unreachable` if it turns out to be failure.
The method that was previously used for computing dual variables was incorrect.
This was used in the integer emptiness check algorithm, where this bug could lead to much longer running times. (Due to the way it is used, this never results in an incorrect emptiness check result.)
This patch fixes the dual computation and adds some additional asserts that catch this bug, along with regression test cases that trigger the asserts when the incorrect dual computation is used.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D113803
This patch provides functionality for simplifying `PresburgerSet`s by checking if any `FlatAffineConstraints` in the set is contained in another, and removing such redundant FACs.
This is part of a series of patches to provide functionality for [integer set coalescing](http://impact.gforge.inria.fr/impact2015/papers/impact2015-verdoolaege.pdf) in MLIR.
Reviewed By: arjunp
Differential Revision: https://reviews.llvm.org/D110617
Previously, when adding a constraint to a Simplex that is already marked
as having no solutions (marked empty), the Simplex would be marked empty again,
and a second UnmarkEmpty entry would be pushed to the undo log. When rolling
back, Simplex should be unmarked empty only after rolling back past the
creation of the first constraint that made it empty.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D114613
Previously, the pivot function would only update the non-redundant rows when
pivoting. This is incorrect because in some cases, when rolling back past a
`detectRedundant` call, the basis being used could be different from that which
was used at the time of returning from the `detectRedundant` call. Therefore,
it is important to update the redundant rows as well during pivots. This could
also be triggered by pivots that occur when testing successive constraints for
being redundant in `detectRedundant` after some initial constraints are marked redundant.
Reviewed By: Groverkss
Differential Revision: https://reviews.llvm.org/D114614
This makes ignoring a result explicit by the user, and helps to prevent accidental errors with dropped results. Marking LogicalResult as no discard was always the intention from the beginning, but got lost along the way.
Differential Revision: https://reviews.llvm.org/D95841
With this, we have complete support for finding integer sample points in FlatAffineConstraints.
Reviewed By: ftynse
Differential Revision: https://reviews.llvm.org/D95047
With this, we have complete support for emptiness checks. This also paves the way for future support to check if two FlatAffineConstraints are equal.
Reviewed By: ftynse
Differential Revision: https://reviews.llvm.org/D94272
Subtraction is a foundational arithmetic operation that is often used when computing, for example, data transfer sets or cache hits. Since the result of subtraction need not be a convex polytope, a new class `PresburgerSet` is introduced to represent unions of convex polytopes.
Reviewed By: ftynse, bondhugula
Differential Revision: https://reviews.llvm.org/D87068
This patch adds the capability to perform constraint redundancy checks for `FlatAffineConstraints` using `Simplex`, via a new member function `FlatAffineConstraints::removeRedundantConstraints`. The pre-existing redundancy detection algorithm runs a full rational emptiness check for each inequality separately for checking redundancy. Leveraging the existing `Simplex` infrastructure, in this patch we have an algorithm for redundancy checks that can check each constraint by performing pivots on the tableau, which provides an alternative to running Fourier-Motzkin elimination for each constraint separately.
Differential Revision: https://reviews.llvm.org/D84935
This patch adds the capability to perform exact integer emptiness checks for FlatAffineConstraints using the General Basis Reduction algorithm (GBR). Previously, only a heuristic was available for emptiness checks, which was not guaranteed to always give a conclusive result.
This patch adds a `Simplex` class, which can be constructed using a `FlatAffineConstraints`, and can find an integer sample point (if one exists) using the GBR algorithm. Additionally, it adds two classes `Matrix` and `Fraction`, which are used by `Simplex`.
The integer emptiness check functionality can be accessed through the new `FlatAffineConstraints::isIntegerEmpty()` function, which runs the existing heuristic first and, if that proves to be inconclusive, runs the GBR algorithm to produce a conclusive result.
Differential Revision: https://reviews.llvm.org/D80860
