Auto merge of #141759 - 1c3t3a:discriminants-query, r=saethlin

Insert checks for enum discriminants when debug assertions are enabled

Similar to the existing null-pointer and alignment checks, this checks for valid enum discriminants on creation of enums through unsafe transmutes. Essentially this sanitizes patterns like the following:
```rust
let val: MyEnum = unsafe { std::mem::transmute<u32, MyEnum>(42) };
```

An extension of this check will be done in a follow-up that explicitly sanitizes for extern enum values that come into Rust from e.g. C/C++.

This check is similar to Miri's capabilities of checking for valid construction of enum values.

This PR is inspired by saethlin@'s PR
https://github.com/rust-lang/rust/pull/104862. Thank you so much for keeping this code up and the detailed comments!

I also pair-programmed large parts of this together with vabr-g@.

r? `@saethlin`

1 files changed, 3 insertions, 0 deletions

diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 38da5c390ef..798f4da9b3b 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -834,6 +834,9 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                 mir::AssertKind::NullPointerDereference => {
                     push_mono_lang_item(self, LangItem::PanicNullPointerDereference);
                 }
+                mir::AssertKind::InvalidEnumConstruction(_) => {
+                    push_mono_lang_item(self, LangItem::PanicInvalidEnumConstruction);
+                }
                 _ => {
                     push_mono_lang_item(self, msg.panic_function());
                 }