The intention of this work is to give MLIR->LLVMIR conversion freedom to
control how the private variable is allocated so that it can be
allocated on the stack in ordinary cases or as part of a structure used
to give closure context for tasks which might outlive the current stack
frame. See RFC:
https://discourse.llvm.org/t/rfc-openmp-supporting-delayed-task-execution-with-firstprivate-variables/83084
For example, a privatizer for an integer used to look like
```mlir
omp.private {type = private} @x.privatizer : !fir.ref<i32> alloc {
^bb0(%arg0: !fir.ref<i32>):
%0 = ... allocate proper memory for the private clone ...
omp.yield(%0 : !fir.ref<i32>)
}
```
After this change, allocation become implicit in the operation:
```mlir
omp.private {type = private} @x.privatizer : i32
```
For more complex types that require initialization after allocation, an
init region can be used:
``` mlir
omp.private {type = private} @x.privatizer : !some.type init {
^bb0(%arg0: !some.pointer<!some.type>, %arg1: !some.pointer<!some.type>):
// initialize %arg1, using %arg0 as a mold for allocations
omp.yield(%arg1 : !some.pointer<!some.type>)
} dealloc {
^bb0(%arg0: !some.pointer<!some.type>):
... deallocate memory allocated by the init region ...
omp.yield
}
```
This patch lays the groundwork for delayed task execution but is not
enough on its own.
After this patch all gfortran tests which previously passed still pass.
There
are the following changes to the Fujitsu test suite:
- 0380_0009 and 0435_0009 are fixed
- 0688_0041 now fails at runtime. This patch is testing firstprivate
variables with tasks. Previously we got lucky with the undefined
behavior and won the race. After these changes we no longer get lucky.
This patch lays the groundwork for a proper fix for this issue.
In flang the lowering re-uses the existing lowering used for reduction
init and dealloc regions.
In flang, before this patch we hit a TODO with the same wording when
generating the copy region for firstprivate polymorphic variables. After
this patch the box-like fir.class is passed by reference into the copy
region, leading to a different path that didn't hit that old TODO but
the generated code still didn't work so I added a new TODO in
DataSharingProcessor.
This enable delayed privatization by default for `omp.wsloop` ops, with
one caveat! I had to workaround the "impure" alloc region issue that
being resolved at the moment. The workaround detects whether the alloc
region's argument is used in the region and at the same time defined in
block that does not dominate the chosen alloca insertion point. If so,
we move the alloca insertion point below the defining instruction of the
alloc region argument. This basically reverts to the
non-delayed-privatizaiton behavior.
nsw is now added to do-variable increment when -fno-wrapv is enabled as
GFortran seems to do.
That means the option introduced by #91579 isn't necessary any more.
Note that the feature of -flang-experimental-integer-overflow is enabled
by default.
This patch simplifies the representation of OpenMP loop wrapper
operations by introducing the `NoTerminator` trait and updating
accordingly the verifier for the `LoopWrapperInterface`.
Since loop wrappers are already limited to having exactly one region
containing exactly one block, and this block can only hold a single
`omp.loop_nest` or loop wrapper and an `omp.terminator` that does not
return any values, it makes sense to simplify the representation of loop
wrappers by removing the terminator.
There is an extensive list of Lit tests that needed updating to remove
the `omp.terminator`s adding some noise to this patch, but actual
changes are limited to the definition of the `omp.wsloop`, `omp.simd`,
`omp.distribute` and `omp.taskloop` loop wrapper ops, Flang lowering for
those, `LoopWrapperInterface::verifyImpl()`, SCF to OpenMP conversion
and OpenMP dialect documentation.
This fixes a bug in OpenMP privatisation. The privatised variables are
created as though they are host associated clones of the original
variables. These privatised variables do not contain the allocatable
attribute themselves and so we need to check if the ultimate symbol is
allocatable. Having or not having this flag influences whether lowering
determines that this is a whole allocatable assignment, which then
causes hlfir.assign not to get the realloc flag, which cases the
allocatable not to be allocated when it is assigned to (leading to a
segfault running the newly added test).
I also did the same for pointer variables because I would imagine they
could experience the same issue.
There is no fallout on tests outside of OpenMP, and the gfortran test
suite still passes, so I think this doesn't break host other kinds of
host associated symbols.
This re-uses reduction declarations from intrinsic operators to add
support for reductions of allocatables, pointers, and arrays with
procedure designators (e.g. min/max).
I have split this into two commits to make it easier to review. The
first one makes the functional change. The second cleans things up now
that we can share much more code between intrinsic operators and
procedure designators.
