commit	8277a65a6b3680e6b01c80c1f7d1dbe5b589ff2e	[log] [tgz]
author	peter klausler <pklausler@nvidia.com>	Mon Dec 07 12:08:58 2020 -0800
committer	Copybara-Service <copybara-worker@google.com>	Tue Dec 08 16:48:03 2020 -0800
tree	6c02f8c0d60ec812db2017ee644597757a5b43a9
parent	cee1a4e1ee15f9ffdcb878df9d7859e552b60387 [diff]

[flang] Improve initializer semantics, esp. for component default values

This patch plugs many holes in static initializer semantics, improves error
messages for default initial values and other component properties in
parameterized derived type instantiations, and cleans up several small
issues noticed during development.  We now do proper scalar expansion,
folding, and type, rank, and shape conformance checking for component
default initializers in derived types and PDT instantiations.
The initial values of named constants are now guaranteed to have been folded
when installed in the symbol table, and are no longer folded or
scalar-expanded at each use in expression folding.  Semantics documentation
was extended with information about the various kinds of initializations
in Fortran and when each of them are processed in the compiler.

Some necessary concomitant changes have bulked this patch out a bit:
* contextual messages attachments, which are now produced for parameterized
  derived type instantiations so that the user can figure out which
  instance caused a problem with a component, have been added as part
  of ContextualMessages, and their implementation was debugged
* several APIs in evaluate::characteristics was changed so that a FoldingContext
  is passed as an argument rather than just its intrinsic procedure table;
  this affected client call sites in many files
* new tools in Evaluate/check-expression.cpp to determine when an Expr
  actually is a single constant value and to validate a non-pointer
  variable initializer or object component default value
* shape conformance checking has additional arguments that control
  whether scalar expansion is allowed
* several now-unused functions and data members noticed and removed
* several crashes and bogus errors exposed by testing this new code
  were fixed
* a -fdebug-stack-trace option to enable LLVM's stack tracing on
  a crash, which might be useful in the future

TL;DR: Initialization processing does more and takes place at the right
times for all of the various kinds of things that can be initialized.

Differential Review: https://reviews.llvm.org/D92783

GitOrigin-RevId: 641ede93efd664cc2e1d1788b195a80b50b36f66

42 files changed

tree: 6c02f8c0d60ec812db2017ee644597757a5b43a9

README.md

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 docs directory. Start with the compiler overview.

To better understand Fortran as a language and the specific grammar accepted by flang, read Fortran For C Programmers and flang's specifications of the Fortran grammar and the OpenMP grammar.

Treatment of language extensions is covered in this document.

To understand the compilers handling of intrinsics, see the discussion of intrinsics.

To understand how a flang program communicates with libraries at runtime, see the discussion of runtime descriptors.

If you're interested in contributing to the compiler, read the style guide and also review how flang uses modern C++ features.

If you are interested in writing new documentation, follow markdown style guide from LLVM.

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

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

Build The New Flang Driver

The new Flang driver, flang-new, is currently under active development and should be considered as an experimental feature. For this reason it is disabled by default. This will change once the new driver replaces the throwaway driver, flang.

In order to build the new driver, add -DFLANG_BUILD_NEW_DRIVER=ON to your CMake invocation line. Additionally, when building out-of-tree, use CLANG_DIR (similarly to LLVM_DIR and MLIR_DIR) to find the installed Clang components.

Note: CLANG_DIR is only required when building the new Flang driver, which currently depends on Clang.

How to Run Tests

Flang supports 2 different categories of tests

Regression tests (https://www.llvm.org/docs/TestingGuide.html#regression-tests)
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 below:

<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

Generate Sphinx-based Documentation

Flang documentation should preferably be written in markdown(.md) syntax (they can be in reStructuredText(.rst) format as well but markdown is recommended in first place), it is mostly meant to be processed by the Sphinx documentation generation system to create HTML pages which would be hosted on the webpage of flang and updated periodically.

If you would like to generate and view the HTML locally:

Install Sphinx, including the sphinx-markdown-tables extension.
Pass -DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF to the cmake command.

cd ~/llvm-project/build
cmake -DLLVM_ENABLE_SPHINX=ON -DSPHINX_WARNINGS_AS_ERRORS=OFF ../llvm
make docs-flang-html

It will generate html in

   $BROWSER <build-dir>/tools/flang/docs/html/