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Rollup merge of #117671 - kjetilkjeka:nvptx_c_abi_avoid_direct, r=davidtwco

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NVPTX: Avoid PassMode::Direct for args in C abi

Fixes #117480

I must admit that I'm confused about `PassMode` altogether, is there a good sum-up threads for this anywhere? I'm especially confused about how "indirect" and "byval" goes together. To me it seems like "indirect" basically means "use a indirection through a pointer", while "byval" basically means "do not use indirection through a pointer".

The return used to keep `PassMode::Direct` for small aggregates. It turns out that `make_indirect` messes up the tests and one way to fix it is to keep `PassMode::Direct` for all aggregates. I have mostly seen this PassMode mentioned for args. Is it also a problem for returns? When experimenting with `byval` as an alternative i ran into [this assert](61a3eea804/compiler/rustc_codegen_llvm/src/abi.rs (L463C22-L463C22))

I have added tests for the same kind of types that is already tested for the "ptx-kernel" abi. The tests cannot be enabled until something like #117458 is completed and merged.

CC: ``@RalfJung`` since you seem to be the expert on this and have already helped me out tremendously

CC: ``@RDambrosio016`` in case this influence your work on `rustc_codegen_nvvm`

``@rustbot`` label +O-NVPTX
This commit is contained in:
Matthias Krüger 2024-05-28 18:04:31 +02:00 • committed by GitHub
commit 713c852a2f
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3 changed files with 440 additions and 5 deletions
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9
compiler/rustc_target/src/abi/call/nvptx64.rs
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@ -11,11 +11,10 @@ fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
}
fn classify_arg<Ty>(arg: &mut ArgAbi<'_, Ty>) {
if arg.layout.is_aggregate() && arg.layout.size.bits() > 64 {
arg.make_indirect();
} else {
// FIXME: this is wrong! Need to decide which ABI we really want here.
arg.make_direct_deprecated();
if arg.layout.is_aggregate() {
arg.make_indirect_byval(None);
} else if arg.layout.size.bits() < 32 {
arg.extend_integer_width_to(32);
}
}