README.md - llvm-project/flang - Git at Google

 # Flang

 Flang is a ground-up implementation of a Fortran front end written in modern
 C++. It started off as the f18 project (https://github.com/flang-compiler/f18)
 with an aim to replace the previous flang project
 (https://github.com/flang-compiler/flang) and address its various deficiencies.
 F18 was subsequently accepted into the LLVM project and rechristened as Flang.

 ## Getting Started

 Read more about flang in the [documentation directory](documentation).
 Start with the [compiler overview](documentation/Overview.md).

 To better understand Fortran as a language
 and the specific grammar accepted by flang,
 read [Fortran For C Programmers](documentation/FortranForCProgrammers.md)
 and
 flang's specifications of the [Fortran grammar](documentation/f2018-grammar.txt)
 and
 the [OpenMP grammar](documentation/OpenMP-4.5-grammar.txt).

 Treatment of language extensions is covered
 in [this document](documentation/Extensions.md).

 To understand the compilers handling of intrinsics,
 see the [discussion of intrinsics](documentation/Intrinsics.md).

 To understand how a flang program communicates with libraries at runtime,
 see the discussion of [runtime descriptors](documentation/RuntimeDescriptor.md).

 If you're interested in contributing to the compiler,
 read the [style guide](documentation/C++style.md)
 and
 also review [how flang uses modern C++ features](documentation/C++17.md).

 ## Supported C++ compilers

 Flang is written in C++17.

 The code has been compiled and tested with
 GCC versions from 7.2.0 to 9.3.0.

 The code has been compiled and tested with
 clang version 7.0, 8.0, 9.0 and 10.0
 using either GNU's libstdc++ or LLVM's libc++.

 The code has been compiled on
 AArch64, x86\_64 and ppc64le servers
 with CentOS7, Ubuntu18.04, Rhel, MacOs, Mojave, XCode and
 Apple Clang version 10.0.1.

 The code does not compile with Windows and a compiler that does not have
 support for C++17.

 ## Building Flang out of tree
 These instructions are for building Flang separately from LLVM; if you are
 building Flang alongside LLVM then follow the standard LLVM build instructions
 and add flang to `LLVM_ENABLE_PROJECTS` instead, as detailed there.

 ### LLVM dependency

 The instructions to build LLVM can be found at
 https://llvm.org/docs/GettingStarted.html. If you are building flang as part
 of LLVM, follow those instructions and add flang to `LLVM_ENABLE_PROJECTS`.

 We highly recommend using the same compiler to compile both llvm and flang.

 The flang CMakeList.txt file uses
 the variable `LLVM_DIR` to find the installed LLVM components
 and
 the variable `MLIR_DIR` to find the installed MLIR components.

 To get the correct LLVM and MLIR libraries included in your flang build,
 define LLVM_DIR and MLIR_DIR on the cmake command line.
 ```
 LLVM=<LLVM_BUILD_DIR>/lib/cmake/llvm \
 MLIR=<LLVM_BUILD_DIR>/lib/cmake/mlir \
 cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ...
 ```
 where `LLVM_BUILD_DIR` is
 the top-level directory where LLVM was built.

 ### Building flang with GCC

 By default,
 cmake will search for g++ on your PATH.
 The g++ version must be one of the supported versions
 in order to build flang.

 Or, cmake will use the variable CXX to find the C++ compiler. CXX should include
 the full path to the compiler or a name that will be found on your PATH, e.g.
 g++-8.3, assuming g++-8.3 is on your PATH.

 ```
 export CXX=g++-8.3
 ```
 or
 ```
 CXX=/opt/gcc-8.3/bin/g++-8.3 cmake ...
 ```

 ### Building flang with clang

 To build flang with clang,
 cmake needs to know how to find clang++
 and the GCC library and tools that were used to build clang++.

 CXX should include the full path to clang++
 or clang++ should be found on your PATH.
 ```
 export CXX=clang++
 ```

 ### Installation Directory

 To specify a custom install location,
 add
 `-DCMAKE_INSTALL_PREFIX=<INSTALL_PREFIX>`
 to the cmake command
 where `<INSTALL_PREFIX>`
 is the path where flang should be installed.

 ### Build Types

 To create a debug build,
 add
 `-DCMAKE_BUILD_TYPE=Debug`
 to the cmake command.
 Debug builds execute slowly.

 To create a release build,
 add
 `-DCMAKE_BUILD_TYPE=Release`
 to the cmake command.
 Release builds execute quickly.

 ### Build Flang out of tree
 ```
 cd ~/flang/build
 cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
 make
 ```
 # How to Run Tests

 Flang supports 2 different categories of tests
 1. Regression tests (https://www.llvm.org/docs/TestingGuide.html#regression-tests)
 2. Unit tests (https://www.llvm.org/docs/TestingGuide.html#unit-tests)

 ## For out of tree builds
 To run all tests:
 ```
 cd ~/flang/build
 cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
 make test check-all
 ```

 To run individual regression tests llvm-lit needs to know the lit
 configuration for flang. The parameters in charge of this are:
 flang_site_config and flang_config. And they can be set as shown bellow:
 ```
 <path-to-llvm-lit>/llvm-lit \
  --param flang_site_config=<path-to-flang-build>/test-lit/lit.site.cfg.py \
  --param flang_config=<path-to-flang-build>/test-lit/lit.cfg.py \
   <path-to-fortran-test>

 ```

 Unit tests:

 If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`ON` by default), it is possible to generate unittests.
 Note: Unit-tests will be skipped for LLVM install for an out-of-tree build as it does not include googletest related headers and libraries.

 There are various ways to run unit-tests.

 ```

 1. make check-flang-unit
 2. make check-all or make check-flang
 3. <path-to-llvm-lit>/llvm-lit \
         test/Unit
 4. Invoking tests from <out-of-tree flang build>/unittests/<respective unit test folder>

 ```


 ## For in tree builds
 If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`On` by default), it is possible to
 generate unittests.

 To run all of the flang unit tests use the `check-flang-unit` target:
 ```
 make check-flang-unit
 ```
 To run all of the flang regression tests use the `check-flang` target:
 ```
 make check-flang
 ```

 # How to Generate Documentation

 ## Generate FIR Documentation
 If flang was built with `-DLINK_WITH_FIR=On` (`On` by default), it is possible to
 generate FIR language documentation by running `make flang-doc`. This will
 create `docs/Dialect/FIRLangRef.md` in flang build directory.

 ## Generate Doxygen-based Documentation
 To generate doxygen-style documentation from source code
 - Pass `-DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON` to the cmake command.

 ```
 cd ~/llvm-project/build
 cmake -DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON ../llvm
 make doxygen-flang

 It will generate html in

     <build-dir>/tools/flang/docs/doxygen/html # for flang docs
 ```
	# Flang

	Flang is a ground-up implementation of a Fortran front end written in modern
	C++. It started off as the f18 project (https://github.com/flang-compiler/f18)
	with an aim to replace the previous flang project
	(https://github.com/flang-compiler/flang) and address its various deficiencies.
	F18 was subsequently accepted into the LLVM project and rechristened as Flang.

	## Getting Started

	Read more about flang in the [documentation directory](documentation).
	Start with the [compiler overview](documentation/Overview.md).

	To better understand Fortran as a language
	and the specific grammar accepted by flang,
	read [Fortran For C Programmers](documentation/FortranForCProgrammers.md)
	and
	flang's specifications of the [Fortran grammar](documentation/f2018-grammar.txt)
	and
	the [OpenMP grammar](documentation/OpenMP-4.5-grammar.txt).

	Treatment of language extensions is covered
	in [this document](documentation/Extensions.md).

	To understand the compilers handling of intrinsics,
	see the [discussion of intrinsics](documentation/Intrinsics.md).

	To understand how a flang program communicates with libraries at runtime,
	see the discussion of [runtime descriptors](documentation/RuntimeDescriptor.md).

	If you're interested in contributing to the compiler,
	read the [style guide](documentation/C++style.md)
	and
	also review [how flang uses modern C++ features](documentation/C++17.md).

	## Supported C++ compilers

	Flang is written in C++17.

	The code has been compiled and tested with
	GCC versions from 7.2.0 to 9.3.0.

	The code has been compiled and tested with
	clang version 7.0, 8.0, 9.0 and 10.0
	using either GNU's libstdc++ or LLVM's libc++.

	The code has been compiled on
	AArch64, x86\_64 and ppc64le servers
	with CentOS7, Ubuntu18.04, Rhel, MacOs, Mojave, XCode and
	Apple Clang version 10.0.1.

	The code does not compile with Windows and a compiler that does not have
	support for C++17.

	## Building Flang out of tree
	These instructions are for building Flang separately from LLVM; if you are
	building Flang alongside LLVM then follow the standard LLVM build instructions
	and add flang to `LLVM_ENABLE_PROJECTS` instead, as detailed there.

	### LLVM dependency

	The instructions to build LLVM can be found at
	https://llvm.org/docs/GettingStarted.html. If you are building flang as part
	of LLVM, follow those instructions and add flang to `LLVM_ENABLE_PROJECTS`.

	We highly recommend using the same compiler to compile both llvm and flang.

	The flang CMakeList.txt file uses
	the variable `LLVM_DIR` to find the installed LLVM components
	and
	the variable `MLIR_DIR` to find the installed MLIR components.

	To get the correct LLVM and MLIR libraries included in your flang build,
	define LLVM_DIR and MLIR_DIR on the cmake command line.
	```
	LLVM=<LLVM_BUILD_DIR>/lib/cmake/llvm \
	MLIR=<LLVM_BUILD_DIR>/lib/cmake/mlir \
	cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ...
	```
	where `LLVM_BUILD_DIR` is
	the top-level directory where LLVM was built.

	### Building flang with GCC

	By default,
	cmake will search for g++ on your PATH.
	The g++ version must be one of the supported versions
	in order to build flang.

	Or, cmake will use the variable CXX to find the C++ compiler. CXX should include
	the full path to the compiler or a name that will be found on your PATH, e.g.
	g++-8.3, assuming g++-8.3 is on your PATH.

	```
	export CXX=g++-8.3
	```
	or
	```
	CXX=/opt/gcc-8.3/bin/g++-8.3 cmake ...
	```

	### Building flang with clang

	To build flang with clang,
	cmake needs to know how to find clang++
	and the GCC library and tools that were used to build clang++.

	CXX should include the full path to clang++
	or clang++ should be found on your PATH.
	```
	export CXX=clang++
	```

	### Installation Directory

	To specify a custom install location,
	add
	`-DCMAKE_INSTALL_PREFIX=<INSTALL_PREFIX>`
	to the cmake command
	where `<INSTALL_PREFIX>`
	is the path where flang should be installed.

	### Build Types

	To create a debug build,
	add
	`-DCMAKE_BUILD_TYPE=Debug`
	to the cmake command.
	Debug builds execute slowly.

	To create a release build,
	add
	`-DCMAKE_BUILD_TYPE=Release`
	to the cmake command.
	Release builds execute quickly.

	### Build Flang out of tree
	```
	cd ~/flang/build
	cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
	make
	```
	# How to Run Tests

	Flang supports 2 different categories of tests
	1. Regression tests (https://www.llvm.org/docs/TestingGuide.html#regression-tests)
	2. Unit tests (https://www.llvm.org/docs/TestingGuide.html#unit-tests)

	## For out of tree builds
	To run all tests:
	```
	cd ~/flang/build
	cmake -DLLVM_DIR=$LLVM -DMLIR_DIR=$MLIR ~/flang/src
	make test check-all
	```

	To run individual regression tests llvm-lit needs to know the lit
	configuration for flang. The parameters in charge of this are:
	flang_site_config and flang_config. And they can be set as shown bellow:
	```
	<path-to-llvm-lit>/llvm-lit \
	--param flang_site_config=<path-to-flang-build>/test-lit/lit.site.cfg.py \
	--param flang_config=<path-to-flang-build>/test-lit/lit.cfg.py \
	<path-to-fortran-test>

	```

	Unit tests:

	If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`ON` by default), it is possible to generate unittests.
	Note: Unit-tests will be skipped for LLVM install for an out-of-tree build as it does not include googletest related headers and libraries.

	There are various ways to run unit-tests.

	```

	1. make check-flang-unit
	2. make check-all or make check-flang
	3. <path-to-llvm-lit>/llvm-lit \
	test/Unit
	4. Invoking tests from <out-of-tree flang build>/unittests/<respective unit test folder>

	```


	## For in tree builds
	If flang was built with `-DFLANG_INCLUDE_TESTS=On` (`On` by default), it is possible to
	generate unittests.

	To run all of the flang unit tests use the `check-flang-unit` target:
	```
	make check-flang-unit
	```
	To run all of the flang regression tests use the `check-flang` target:
	```
	make check-flang
	```

	# How to Generate Documentation

	## Generate FIR Documentation
	If flang was built with `-DLINK_WITH_FIR=On` (`On` by default), it is possible to
	generate FIR language documentation by running `make flang-doc`. This will
	create `docs/Dialect/FIRLangRef.md` in flang build directory.

	## Generate Doxygen-based Documentation
	To generate doxygen-style documentation from source code
	- Pass `-DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON` to the cmake command.

	```
	cd ~/llvm-project/build
	cmake -DLLVM_ENABLE_DOXYGEN=ON -DFLANG_INCLUDE_DOCS=ON ../llvm
	make doxygen-flang

	It will generate html in

	<build-dir>/tools/flang/docs/doxygen/html # for flang docs
	```