Backport #148214#189
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This adds the simplest implementation of `PreserveMost` calling convention and we preserve `x5-x31` (except x6/x7/x28) registers. Fixes llvm#148147.
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Why is this being submitted as a backport against the Rust LLVM fork? |
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With this backport, this test can pass. |
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This shoud be backported to the upstream if possible. See also https://rustc-dev-guide.rust-lang.org/backend/updating-llvm.html. |
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See: llvm#158401 |
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llvm#158402 has been merged. |
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rust-lang/rust#146953 includes this backport. |
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Flang uses the OMPIRBuilder to lower OpenMP constructs to LLVM IR. When dealing with work sharing constructs, such as DO, DISTRIBUTE or SECTIONS/SECTION, OMPIRBuilder needs to construct the call to the OpenMP runtime, typically `__kmpc_for_static_init` or `__kmpc_dist_for_static_init`. The first passed flag to these functions is the `ident_t` struct, defined in `kmp.h`. Most of the arguments are reserved for usage in Fortran and unused in `openmp`. However, the `flags` argument is used throughout the code base to identify specific constructs, such as the type of work sharing construct. In llvm#112545, it was identified that Flang does not provide the correct `ident_t` flags when calling into e.g. `__kmpc_for_static_init`, causing the following runtime warning to appear when the OpenMP Tools Interface is used: ``` OMP: Warning rust-lang#189: OMPT: Cannot determine workshare type; using the default (loop) instead. This issue is fixed in an up-to-date compiler. ``` This PR adds a test, verifying that the work sharing constructs provide the correct flags to the runtime call. The IR check for SECTIONS/SECTION maps against `KMP_IDENT_WORK_LOOP`, as the OMPIRBuilder converts the SECTIONS construct into a DO loop with a switch-case for every SECTION clause. In addition, `OMPIRBuilder` is modified, so that the work loop type is passed via `ident_t.flags` to the respective `__kmpc_for_static_init`/`__kmpc_dist_for_static_init` calls, letting the test pass and the `libomp` warning disappear. Wherever possible, provide the mapping based on the passed `LoopType`. If not available, I implemented the decision based on the `DistScheduleSchedType`, or in case of `applyDynamicWorkshareLoop`, hard-coded this to `OMP_IDENT_FLAG_WORK_LOOP`. --- As this is the first time dealing with `OMPIRBuilder`, I'm not sure if I missed anything while implementing these changes. If there's anything that can be improved here, e.g. with the ident flag mapping, I'm very grateful for any feedback. I tried to implement this with the best of my understanding based on taking a look at the existing code and tests. For example, I was not sure if adding a test to `flang/test/Integration/OpenMP/` is the correct approach here, or if I rather should try to modify `unittests/Frontend/OpenMPIRBuilderTest.cpp`. In the end, the former looked to me more straight-forward. --- Fixes llvm#112545 --------- Signed-off-by: Jan André Reuter <j.reuter@fz-juelich.de>
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Backport llvm#148214
[RISCV] Support PreserveMost calling convention (llvm#148214)
This adds the simplest implementation of
PreserveMostcalling convention and we preservex5-x31(except x6/x7/x28) registers.Fixes llvm#148147.