d26a6464f8
Descriptor addendum have a field to hold length parameters (currently
only one). This field is currently never used because flang does not
lowered derived types with length parameters.
However, leaving it uninitialized is causing bugs in code like gFTL
where the code is trying to sort POINTERs (see [1]). More precisely, it
is an issue when two pointers should compare equal (same base address),
because the uninitialized values in the addendum may differ depending on
the "stack history" and optimization level.
Always initialized the length parameters field in the addendum to zero.
[1]:
dc93a5fc2f/include/v1/templates/set_impl.inc (L312)
The type being transferred to an integer array may look like:
```
TYPE :: localwrapper
TYPE(T), POINTER :: item
END TYPE localwrapper
```
Which in flang case ends-up transferring a descriptor to an integer
array, the code in gFTL later compare the integer arrays. This logic is
used when building set data structures in gFTL.
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.