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88 lines
3.0 KiB
Markdown
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# Flang 12.0.0 (In-Progress) Release Notes
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> **warning**
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>
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> These are in-progress notes for the upcoming LLVM 12.0.0 release.
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> Release notes for previous releases can be found on [the Download
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> Page](https://releases.llvm.org/download.html).
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## Introduction
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This document contains the release notes for the Flang Fortran frontend,
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part of the LLVM Compiler Infrastructure, release 12.0.0. Here we
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describe the status of Flang in some detail, including major
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improvements from the previous release and new feature work. For the
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general LLVM release notes, see [the LLVM
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documentation](https://llvm.org/docs/ReleaseNotes.html). All LLVM
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releases may be downloaded from the [LLVM releases web
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site](https://llvm.org/releases/).
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Note that if you are reading this file from a Git checkout, this
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document applies to the *next* release, not the current one. To see the
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release notes for a specific release, please see the [releases
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page](https://llvm.org/releases/).
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## Known Issues
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These are issues that couldn't be fixed before the release. See the bug
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reports for the latest status.
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* ...
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## Introducing Flang
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Flang is LLVM's Fortran front end and is new for the LLVM 11 release.
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Flang is still a work in progress for this release and is included for
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experimentation and feedback.
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Flang is able to parse a comprehensive subset of the Fortran language
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and check it for correctness. Flang is not yet able to generate LLVM IR
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for the source code and thus is unable to compile a running binary.
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Flang is able to unparse the input source code into a canonical form and
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emit it to allow testing. Flang can also invoke an external Fortran
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compiler on this canonical input.
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Flang's parser has comprehensive support for:
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* Fortran 2018
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* OpenMP 4.5
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* OpenACC 3.0
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Interested users are invited to try to compile their Fortran codes with
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flang in and report any issues in parsing or semantic checking in
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[bugzilla](https://bugs.llvm.org/enter_bug.cgi?product=flang).
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### Major missing features
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* Flang is not supported on Windows platforms.
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## Using Flang
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Usage: `flang hello.f90 -o hello.bin`
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By default, Flang will parse the Fortran file `hello.f90` then unparse it to a
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canonical Fortran source file. Flang will then invoke an external
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Fortran compiler to compile this source file and link it, placing the
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resulting executable in `hello.bin`.
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To specify the external Fortran compiler, set the `F18_FC` environment
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variable to the name of the compiler binary and ensure that it is on your
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`PATH`. The default value for `F18_FC` is `gfortran`.
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When invoked with no source input, Flang will wait for input on stdin.
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When invoked in this way, Flang performs the same actions as if
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called with `-fdebug-measure-parse-tree -funparse` and does not invoke
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`F18_FC`.
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For a full list of options that Flang supports, run `flang --help`.
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## Additional Information
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Flang's documentation is located in the `flang/docs/` directory in the
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LLVM monorepo.
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If you have any questions or comments about Flang, please feel free to
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contact us via the [mailing
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list](https://lists.llvm.org/mailman/listinfo/flang-dev).
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