bd30838422
The current implementation of OpenACC lowering includes explicit
expansion of following cases:
- Creation of `acc.bounds` operations for all arrays, including those
whose dimensions are captured in the type (eg `!fir.array<100xf32>`)
- Expansion of box types by only putting the box's address in the data
clause. The address was extracted with a `fir.box_addr` operation and
the bounds were filled with `fir.box_dims` operation.
However, with the creation of the new type interface `MappableType`, the
idea is that specific type-based semantics can now be used. This also
really simplifies representation in the IR. Consider the following
example:
```
subroutine sub(arr)
real :: arr(:)
!$acc enter data copyin(arr)
end subroutine
```
Before the current PR, the relevant acc dialect IR looked like:
```
func.func @_QPsub(%arg0: !fir.box<!fir.array<?xf32>> {fir.bindc_name =
"arr"}) {
...
%1:2 = hlfir.declare %arg0 dummy_scope %0 {uniq_name = "_QFsubEarr"} :
(!fir.box<!fir.array<?xf32>>, !fir.dscope) ->
(!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
%c1 = arith.constant 1 : index
%c0 = arith.constant 0 : index
%2:3 = fir.box_dims %1#0, %c0 : (!fir.box<!fir.array<?xf32>>, index)
-> (index, index, index)
%c0_0 = arith.constant 0 : index
%3 = arith.subi %2#1, %c1 : index
%4 = acc.bounds lowerbound(%c0_0 : index) upperbound(%3 : index)
extent(%2#1 : index) stride(%2#2 : index) startIdx(%c1 : index)
{strideInBytes = true}
%5 = fir.box_addr %1#0 : (!fir.box<!fir.array<?xf32>>) ->
!fir.ref<!fir.array<?xf32>>
%6 = acc.copyin varPtr(%5 : !fir.ref<!fir.array<?xf32>>) bounds(%4) ->
!fir.ref<!fir.array<?xf32>> {name = "arr", structured = false}
acc.enter_data dataOperands(%6 : !fir.ref<!fir.array<?xf32>>)
```
After the current change, it looks like:
```
func.func @_QPsub(%arg0: !fir.box<!fir.array<?xf32>> {fir.bindc_name =
"arr"}) {
...
%1:2 = hlfir.declare %arg0 dummy_scope %0 {uniq_name = "_QFsubEarr"} :
(!fir.box<!fir.array<?xf32>>, !fir.dscope) ->
(!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
%2 = acc.copyin var(%1#0 : !fir.box<!fir.array<?xf32>>) ->
!fir.box<!fir.array<?xf32>> {name = "arr", structured = false}
acc.enter_data dataOperands(%2 : !fir.box<!fir.array<?xf32>>)
```
Restoring the old behavior can be done with following command line
options:
`--openacc-unwrap-fir-box=true --openacc-generate-default-bounds=true`
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.