87bab31c27
Add support for inlining hlfir.assign operations where the LHS is an allocatable and the RHS is an `hlfir.expr` (e.g., from `hlfir.elemental`). Since `hlfir.expr` values cannot alias with memory locations, these assignments can be safely inlined without alias analysis. The optimization is controlled by the -inline-hlfir-allocatable-expr-assign flag: fir-opt -inline-hlfir-allocatable-expr-assign --inline-hlfir-assign file.fir flang -mmlir -inline-hlfir-allocatable-expr-assign file.f90 The generated code uses `fir:🏭:genReallocIfNeeded` to properly handle Fortran allocatable assignment semantics (F2018 10.2.1.3): - If not allocated: allocate with RHS shape - If allocated with same shape: reuse existing allocation - If allocated with different shape: reallocate This is motivated by the increased link time that I am seeing when `__FortranAAssign` is called from the user code. The details of the problem are documented in https://github.com/llvm/llvm-project/issues/187720
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.
Please note that flang is not ready yet for production usage.
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 LLVM's Markdown style guide.
Consult the Getting Started with Flang for information on building and running flang.