[all-commits] [llvm/llvm-project] 9050b2: [OpenMPIRBuilder] Remove wrapper function in `crea...

[Shraiysh via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9050b27bd531f14f5f700ea27f4ca1f2e38bc8c6
      https://github.com/llvm/llvm-project/commit/9050b27bd531f14f5f700ea27f4ca1f2e38bc8c6
  Author: Shraiysh <Shraiysh.Vaishay at amd.com>
  Date:   2023-10-09 (Mon, 09 Oct 2023)

  Changed paths:
    M llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
    M llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
    M mlir/test/Target/LLVMIR/openmp-llvm.mlir
    M mlir/test/Target/LLVMIR/openmp-teams.mlir

  Log Message:
  -----------
  [OpenMPIRBuilder] Remove wrapper function in `createTask`, `createTeams` (#67723)

This patch removes the wrapper function in `OpenMPIRBuilder::createTask`
and `OpenMPIRBuilder.createTeams`. The outlined function is directly of
the form that is expected by the runtime library calls. This patch also
adds a utility function to help add fake values and their uses, which
will be deleted in finalization callbacks.

**Why we needed wrappers earlier?**
Before the post outline callbacks are executed, the IR has the following
structure:
```
define @func() {
  ;...
  call void @outlined_fn(ptr %data)
  ;...
}
define void @outlined_fn(ptr %data)
```
OpenMP offloading expects a specific signature for the outlined function
in a runtime call. For example, `__kmpc_fork_teams` expects the
following signature:
```
define @outlined_fn(ptr %global.tid, ptr %data)
```
As there is no way to change a function's arguments after it has been
created, a wrapper function with the expected signature is created that
calls the outlined function inside it.

**How we are handling it now?**
To handle this in the current patch, we create a "fake" global tid and
add a "fake" use for it in the to-be-outlined region. We need to create
these fake values so the outliner sees it as something it needs to pass
to the outlined function. We also tell the outliner to exclude this
global tid value from the aggregate `data` argument, so it comes as a
separate argument in the beginning. This way, we are able to directly
get the outlined function in the expected format. This is inspired by
the way `createParallel` handles outlining (using fake values and then
deleting them later). Tasks are handled with a similar approach. This
simplifies the generated code and the code to do this itself also
becomes simpler (because we no longer have to construct a new function).