[flang][OpenMP] Rework LINEAR clause (#119278)

The OmpLinearClause class was a variant of two classes, one for when the
linear modifier was present, and one for when it was absent. These two
class

[flang][OpenMP] Rework LINEAR clause (#119278)

The OmpLinearClause class was a variant of two classes, one for when the
linear modifier was present, and one for when it was absent. These two
classes did not follow the conventions for parse tree nodes, (i.e.
tuple/wrapper/union formats), which necessitated specialization of the
parse tree visitor.

The new form of OmpLinearClause is the standard tuple with a list of
modifiers and an object list. The specialization of parse tree visitor
for it has been removed.
Parsing and unparsing of the new form bears additional complexity due to
syntactical differences between OpenMP 5.2 and prior versions: in OpenMP
5.2 the argument list is post-modified, while in the prior versions, the
step modifier was a post-modifier while the linear modifier had an
unusual syntax of `modifier(list)`.

With this change the LINEAR clause is no different from any other
clauses in terms of its structure and use of modifiers. Modifier
validation and all other checks work the same as with other clauses.

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[flang][OpenMP] Use new modifiers in ALLOCATE clause (#117627)

Again, this simplifies the semantic checks and lowering quite a bit.
Update the check for positive alignment to use a more informative

[flang][OpenMP] Use new modifiers in ALLOCATE clause (#117627)

Again, this simplifies the semantic checks and lowering quite a bit.
Update the check for positive alignment to use a more informative
message, and to highlight the modifier itsef, not the whole clause.
Remove the checks for the allocator expression itself being positive:
there is nothing in the spec that says that it should be positive.

Remove the "simple" modifier from the AllocateT template, since both
simple and complex modifiers are the same thing, only differing in
syntax.

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[Frontend][OpenMP] Allow implicit clauses to fail to apply (#100460)

The `linear(x)` clause implies `firstprivate(x)` on the compound
construct if `x` is not an induction variable. With more constr

[Frontend][OpenMP] Allow implicit clauses to fail to apply (#100460)

The `linear(x)` clause implies `firstprivate(x)` on the compound
construct if `x` is not an induction variable. With more construct
combinations coming in OpenMP 6.0, the `firstprivate` clause may not be
possible to apply, e.g. in "masked simd".
An additional benefit from this change is that it allows treating leaf
constructs as combined constructs with a single constituent. Otherwise,
a `linear` clause on a lone `simd` construct could imply a
`firstprivate` clause that can't be applied.

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[Flang][OpenMP] Lowering Order clause to MLIR (#96730)

[Frontend][OpenMP] Remove `reduction` from allowed clauses for `target` (#90754)

The "reduction" clause is not allowed on the "target" construct.

[Frontend][OpenMP] Privatizing clauses in construct decomposition (#92176)

Add remaining clauses with the "privatizing" property to construct
decomposition, specifically to the part handling the `a

[Frontend][OpenMP] Privatizing clauses in construct decomposition (#92176)

Add remaining clauses with the "privatizing" property to construct
decomposition, specifically to the part handling the `allocate` clause.

---------

Co-authored-by: Tom Eccles <t@freedommail.info>

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[flang][OpenMP] Decompose compound constructs, do recursive lowering (#90098)

A compound construct with a list of clauses is broken up into individual
leaf/composite constructs. Each such construct

[flang][OpenMP] Decompose compound constructs, do recursive lowering (#90098)

A compound construct with a list of clauses is broken up into individual
leaf/composite constructs. Each such construct has the list of clauses
that apply to it based on the OpenMP spec.

Each lowering function (i.e. a function that generates MLIR ops) is now
responsible for generating its body as described below.

Functions that receive AST nodes extract the construct, and the clauses
from the node. They then create a work queue consisting of individual
constructs, and invoke a common dispatch function to process (lower) the
queue.

The dispatch function examines the current position in the queue, and
invokes the appropriate lowering function. Each lowering function
receives the queue as well, and once it needs to generate its body, it
either invokes the dispatch function on the rest of the queue (if any),
or processes nested evaluations if the work queue is at the end.

Re-application of ca1bd5995f6ed934f9187305190a5abfac049173 with fixes for
compilation errors.

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[flang][OpenMP] Decompose compound constructs, do recursive lowering (#90098)

A compound construct with a list of clauses is broken up into individual
leaf/composite constructs. Each such construct

[flang][OpenMP] Decompose compound constructs, do recursive lowering (#90098)

A compound construct with a list of clauses is broken up into individual
leaf/composite constructs. Each such construct has the list of clauses
that apply to it based on the OpenMP spec.

Each lowering function (i.e. a function that generates MLIR ops) is now
responsible for generating its body as described below.

Functions that receive AST nodes extract the construct, and the clauses
from the node. They then create a work queue consisting of individual
constructs, and invoke a common dispatch function to process (lower) the
queue.

The dispatch function examines the current position in the queue, and
invokes the appropriate lowering function. Each lowering function
receives the queue as well, and once it needs to generate its body, it
either invokes the dispatch function on the rest of the queue (if any),
or processes nested evaluations if the work queue is at the end.

show more ...