[flang][acc] Fix the indexing of the reduction combiner for multidimensional static arrays (#155536)
In the following example of reducing a static 2D array, we have
incorrect coordinates for array access in the reduction combiner. This
PR reverses the order of the induction variables used for such array
indexing. For other cases of static arrays, we reverse the loop order as
well so that the innermost loop can handle the innermost dimension.
```Fortran
program main
implicit none
integer, parameter :: m = 2
integer, parameter :: n = 10
integer :: r(n,m), i
r = 0
!$acc parallel loop reduction(+:r(:n,:m))
do i = 1, n
r(i, 1) = i
enddo
print *, r
end program main
```
Currently, we have:
```mlir
fir.do_loop %arg2 = %c0 to %c1 step %c1 {
fir.do_loop %arg3 = %c0 to %c9 step %c1 {
%0 = fir.coordinate_of %arg0, %arg2, %arg3 : (!fir.ref<!fir.array<10x2xi32>>, index, index) -> !fir.ref<i32>
%1 = fir.coordinate_of %arg1, %arg2, %arg3 : (!fir.ref<!fir.array<10x2xi32>>, index, index) -> !fir.ref<i32>
```
We'll obtain:
```mlir
fir.do_loop %arg2 = %c0 to %c1 step %c1 {
fir.do_loop %arg3 = %c0 to %c9 step %c1 {
%0 = fir.coordinate_of %arg0, %arg3, %arg2 : (!fir.ref<!fir.array<10x2xi32>>, index, index) -> !fir.ref<i32>
%1 = fir.coordinate_of %arg1, %arg3, %arg2 : (!fir.ref<!fir.array<10x2xi32>>, index, index) -> !fir.ref<i32>
```
llvm-project
9a81d853 - [flang][acc] Fix the indexing of the reduction combiner for multidimensional static arrays (#155536)
