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, 6 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 3df97429e09..1d5fbfc0896 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -776,6 +776,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 // `#[track_caller]` adds an implicit argument.
                 (LangItem::PanicNullPointerDereference, vec![location])
             }
+            AssertKind::InvalidEnumConstruction(source) => {
+                let source = self.codegen_operand(bx, source).immediate();
+                // It's `fn panic_invalid_enum_construction(source: u128)`,
+                // `#[track_caller]` adds an implicit argument.
+                (LangItem::PanicInvalidEnumConstruction, vec![source, location])
+            }
             _ => {
                 // It's `pub fn panic_...()` and `#[track_caller]` adds an implicit argument.
                 (msg.panic_function(), vec![location])