[flang] Handle USE association in parse tree rewriting

f18 was treating "f() = 1" as a statement function definition
if it could be viewed as being in the specification part and
"f" was a USE-associ

[flang] Handle USE association in parse tree rewriting

f18 was treating "f() = 1" as a statement function definition
if it could be viewed as being in the specification part and
"f" was a USE-associated function returning a data pointer.
(The non-USE-associated case is fine.) Fix to allow for "f"
to be USE associated.

Differential Revision: https://reviews.llvm.org/D127430

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[flang] Disambiguate F(X)=Y case where F is a function returning a pointer

F(X)=Y may be initially parsed as a statement function definition; an
existing pass will detect statement functions that sh

[flang] Disambiguate F(X)=Y case where F is a function returning a pointer

F(X)=Y may be initially parsed as a statement function definition; an
existing pass will detect statement functions that should be rewritten
into assignment statemets with array element references as their
left-hand side variables. However, F() may also be a reference to a
function that returns a data pointer, and f18 did not handle this
case correctly.

The right fix is to rewrite the parse tree for F(X)=Y into an assignment
to a function reference result. The cases that are actually assignments
to array elements -- including all of the cases previously handled --
will have their left-hand sides converted to array element references
later by another existing rewriting step.

Differential Revision: https://reviews.llvm.org/D124299

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[flang] Add & use a better visit() (take 2)

Adds flang/include/flang/Common/log2-visit.h, which defines
a Fortran::common::visit() template function that is a drop-in
replacement for std::visit().

[flang] Add & use a better visit() (take 2)

Adds flang/include/flang/Common/log2-visit.h, which defines
a Fortran::common::visit() template function that is a drop-in
replacement for std::visit(). Modifies most use sites in
the front-end and runtime to use common::visit().

The C++ standard mandates that std::visit() have O(1) execution
time, which forces implementations to build dispatch tables.
This new common::visit() is O(log2 N) in the number of alternatives
in a variant<>, but that N tends to be small and so this change
produces a fairly significant improvement in compiler build
memory requirements, a 5-10% improvement in compiler build time,
and a small improvement in compiler execution time.

Building with -DFLANG_USE_STD_VISIT causes common::visit()
to be an alias for std::visit().

Calls to common::visit() with multiple variant arguments
are referred to std::visit(), pending further work.

This change is enabled only for GCC builds with GCC >= 9;
an earlier attempt (D122441) ran into bugs in some versions of
clang and was reverted rather than simply disabled; and it is
not well tested with MSVC. In non-GCC and older GCC builds,
common::visit() is simply an alias for std::visit().

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Revert "[flang] Add & use a better visit()"

This reverts commit 2ab9990c9eb79682a4d4b183dfbc7612d3e55328. It has
caused multiple build failures:
* https://lab.llvm.org/buildbot/#/builders/177/build

Revert "[flang] Add & use a better visit()"

This reverts commit 2ab9990c9eb79682a4d4b183dfbc7612d3e55328. It has
caused multiple build failures:
* https://lab.llvm.org/buildbot/#/builders/177/builds/4346
* https://lab.llvm.org/buildbot/#/builders/180/builds/3803
* https://lab.llvm.org/buildbot/#/builders/175/builds/10419
* https://lab.llvm.org/buildbot/#/builders/191/builds/4318
* https://lab.llvm.org/buildbot/#/builders/173/builds/4274
* https://lab.llvm.org/buildbot/#/builders/181/builds/4297

All these bots failed with a time-out:
```
command timed out: 1200 seconds without output running [b'ninja', b'-j', b'32'], attempting to kill
```
I'm guessing that that's due to template instantiations failing at some
point (https://reviews.llvm.org/D122441 introduced a custom
implementation of std::visit). Everything seems fine when either:
* building on X86 with GCC or Clang (tested with GCC 9.3 and Clang 12)
* building on AArch64 with GCC (tested with GCC 11)

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[flang] Add & use a better visit()

Adds flang/include/flang/Common/visit.h, which defines
a Fortran::common::visit() template function that is a drop-in
replacement for std::visit(). Modifies most

[flang] Add & use a better visit()

Adds flang/include/flang/Common/visit.h, which defines
a Fortran::common::visit() template function that is a drop-in
replacement for std::visit(). Modifies most use sites in
the front-end and runtime to use common::visit().

The C++ standard mandates that std::visit() have O(1) execution
time, which forces implementations to build dispatch tables.
This new common::visit() is O(log2 N) in the number of alternatives
in a variant<>, but that N tends to be small and so this change
produces a fairly significant improvement in compiler build
memory requirements, a 5-10% improvement in compiler build time,
and a small improvement in compiler execution time.

Building with -DFLANG_USE_STD_VISIT causes common::visit()
to be an alias for std::visit().

Calls to common::visit() with multiple variant arguments
are referred to std::visit(), pending further work.

Differential Revision: https://reviews.llvm.org/D122441

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[flang] Clean up TODO comments and fix one (DATA constant ambiguity)

Remove resolved & moot TODO comments in Common/, Parser/,
and Evaluate/. Address a pending one relating to parsing
ambiguity in

[flang] Clean up TODO comments and fix one (DATA constant ambiguity)

Remove resolved & moot TODO comments in Common/, Parser/,
and Evaluate/. Address a pending one relating to parsing
ambiguity in DATA statement constants, handling it with
symbol table information in Semantics and adding a test.

Differential Revision: https://reviews.llvm.org/D93323

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[flang] Include source information in an invalid file-unit-number message

An io-unit that is an internal-file-variable is syntactically identical
to a file-unit-number expression that is a variable

[flang] Include source information in an invalid file-unit-number message

An io-unit that is an internal-file-variable is syntactically identical
to a file-unit-number expression that is a variable reference. An
ambiguous unit is initially parsed as an internal-file-variable. If
semantic analysis determines that the unit is not of character type,
it is rewritten as an internal-file-variable. This modification must
retain source coordinate information.

Differential revision: https://reviews.llvm.org/D91375

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[flang] Detect and rewrite ambiguous READ(CVAR)[,item-list]

READ(CVAR)[,item-list] with a character variable CVAR
could be parsed as an unformatted READ from an internal
unit or as a formatted READ

[flang] Detect and rewrite ambiguous READ(CVAR)[,item-list]

READ(CVAR)[,item-list] with a character variable CVAR
could be parsed as an unformatted READ from an internal
unit or as a formatted READ from the default external unit
with a needlessly parenthesized variable format. We parse
it as the former, but Fortran doesn't have unformatted
internal I/O.

Differential revision: https://reviews.llvm.org/D90493

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[flang] DATA stmt processing (part 3/4): Remaining prep work

Rolls up small changes across the frontend to prepare for the large
forthcoming patch (part 4/4) that completes DATA statement processing

[flang] DATA stmt processing (part 3/4): Remaining prep work

Rolls up small changes across the frontend to prepare for the large
forthcoming patch (part 4/4) that completes DATA statement processing
via conversion to initializers.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D82137

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[flang] Process names in ASSIGN and assigned GOTO

Allow ASSIGNed integer variables as formats

Address review comment

Original-commit: flang-compiler/f18@361a151508b4a1940fc0669dead180be67964d8d
Re

[flang] Process names in ASSIGN and assigned GOTO

Allow ASSIGNed integer variables as formats

Address review comment

Original-commit: flang-compiler/f18@361a151508b4a1940fc0669dead180be67964d8d
Reviewed-on: https://github.com/flang-compiler/f18/pull/1099

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[flang] Reformat with latest clang-format and .clang-format

Original-commit: flang-compiler/f18@9fe84f45d7fd685051004678d6b5775dcc4c6f8f
Reviewed-on: https://github.com/flang-compiler/f18/pull/1094

[flang] [LLVMify F18] Compiler module folders should have capitalised names (flang-compiler/f18#980)

This patch renames the modules in f18 to use a capital letter in the
module name

Signed-off-b

[flang] [LLVMify F18] Compiler module folders should have capitalised names (flang-compiler/f18#980)

This patch renames the modules in f18 to use a capital letter in the
module name

Signed-off-by: Caroline Concatto <[email protected]>

Original-commit: flang-compiler/f18@d2eb7a1c443d1539ef12b6f027074a0eb15b1ea0
Reviewed-on: https://github.com/flang-compiler/f18/pull/980

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