Mark unions non-const-propagatable in `KnownPanicsLint` without calling layout
Fixes#123710
The ICE occurs during the layout calculation of the union `InvalidTag` in #123710 because the following assert fails:5fe8b697e7/compiler/rustc_abi/src/layout.rs (L289-L292)
The layout calculation is invoked by `KnownPanicsLint` when it is trying to figure out which locals it can const prop. Since `KnownPanicsLint` is never actually going to const props unions thanks to PR https://github.com/rust-lang/rust/pull/121628 there's no point calling layout to check if it can. So in this fix I skip the call to layout and just mark the local non-const propagatable if it is a union.
This is serves as a collection of crashes so that accidental ICE fixes are tracked.
This was formally done at https://github.com/rust-lang/glacier but doing it inside
the rustc testsuite is more convenient.
It is imperative that a test in the suite causes an internal compiler error/panic
or makes rustc crash in some other way.
A test will "pass" if rustc exits with something other than 1 or 0.
When adding crashes from https://github.com/rust-lang/rust/issues, the
issue number should be noted in the file name (12345.rs should suffice)
and perhaps also inside the file via //@ known-bug #4321
If you happen to fix one of the crashes, please move it to a fitting
subdirectory in tests/ui and give it a meaningful name.
Also please add a doc comment at the top of the file explaining why
this test exists. :)
Adding
Fixes #NNNNN
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43265f5721