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Auto merge of #120500 - oli-obk:intrinsics2.0, r=WaffleLapkin

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Implement intrinsics with fallback bodies

fixes #93145 (though we can port many more intrinsics)
cc #63585

The way this works is that the backend logic for generating custom code for intrinsics has been made fallible. The only failure path is "this intrinsic is unknown". The `Instance` (that was `InstanceDef::Intrinsic`) then gets converted to `InstanceDef::Item`, which represents the fallback body. A regular function call to that body is then codegenned. This is currently implemented for

* codegen_ssa (so llvm and gcc)
* codegen_cranelift

other backends will need to adjust, but they can just keep doing what they were doing if they prefer (though adding new intrinsics to the compiler will then require them to implement them, instead of getting the fallback body).

cc `@scottmcm` `@WaffleLapkin`

### todo

* [ ] miri support
* [x] default intrinsic name to name of function instead of requiring it to be specified in attribute
* [x] make sure that the bodies are always available (must be collected for metadata)
This commit is contained in:
bors 2024-02-16 09:53:01 +00:00
commit dfa88b328f
49 changed files with 621 additions and 452 deletions
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15
compiler/rustc_monomorphize/src/collector.rs
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@ -956,19 +956,24 @@ fn visit_instance_use<'tcx>(
if !should_codegen_locally(tcx, &instance) {
return;
}
// The intrinsics assert_inhabited, assert_zero_valid, and assert_mem_uninitialized_valid will
// be lowered in codegen to nothing or a call to panic_nounwind. So if we encounter any
// of those intrinsics, we need to include a mono item for panic_nounwind, else we may try to
// codegen a call to that function without generating code for the function itself.
if let ty::InstanceDef::Intrinsic(def_id) = instance.def {
let name = tcx.item_name(def_id);
if let Some(_requirement) = ValidityRequirement::from_intrinsic(name) {
// The intrinsics assert_inhabited, assert_zero_valid, and assert_mem_uninitialized_valid will
// be lowered in codegen to nothing or a call to panic_nounwind. So if we encounter any
// of those intrinsics, we need to include a mono item for panic_nounwind, else we may try to
// codegen a call to that function without generating code for the function itself.
let def_id = tcx.lang_items().get(LangItem::PanicNounwind).unwrap();
let panic_instance = Instance::mono(tcx, def_id);
if should_codegen_locally(tcx, &panic_instance) {
output.push(create_fn_mono_item(tcx, panic_instance, source));
}
} else if tcx.has_attr(def_id, sym::rustc_intrinsic) {
// Codegen the fallback body of intrinsics with fallback bodies
let instance = ty::Instance::new(def_id, instance.args);
if should_codegen_locally(tcx, &instance) {
output.push(create_fn_mono_item(tcx, instance, source));
}
}
}