Fix ICE for repr simd on non struct

[chenyukang]

Fixes #148634

The ICE happened because

rust/compiler/rustc_middle/src/ty/mod.rs

Line 1531 in 995c118

attr::ReprSimd => ReprFlags::IS_SIMD,

will always set IS_SIMD according to get_all_attrs, and since we already report error attribute should be applied to a struct, it's OK to bypass here.

[rustbot]

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[Kivooeo]

r=me when ci is green

[lcnr]

hmm, would it be possible to instead filter the ReprOptions so that we don't end up with unsupported ones? It feels brittle to simply handle incorrect info by ignoring it, e.g. it adds an implicit assumption that repr(simd) is only ever used for structs, and if we were to idk, extend support to unions at some point (even if unlikely) this code would suddenly be incorrect

alternatively, accept all Adts, but then match on the kind and skip + span_delay_bug if it's not a struct

[Kivooeo]

it adds an implicit assumption that repr(simd) is only ever used for structs

according to the rfc it seems (at least for me) that this is only for structs https://github.com/rust-lang/rfcs/blob/master/text/1199-simd-infrastructure.md#types

[lcnr]

Yes, but is this a guarantee that we'll never extend it to unions? My point is not that the code is wrong, it's that this code adds an implicit dependency which may result in bugs in the future.

Most bugs in large projects happen by:

• somebody writes code which has an unchecked assumption which holds right now
• somebody else modifies another part of the project, causing this assumption to no longer hold, resulting in a bug in entirely untouched code

This implies that a good way to avoid bugs in large projects it to avoid unchecked assumptions. It's why exhaustive matches are so powerful. It's also why we do stuff like

rust/compiler/rustc_middle/src/ty/context.rs

Lines 628 to 635 in 0bbef55

	// This causes a compiler error if any new float kinds are added.
	let (ty::FloatTy::F16 | ty::FloatTy::F32 | ty::FloatTy::F64 | ty::FloatTy::F128);
	let possible_floats = [
	ty::SimplifiedType::Float(ty::FloatTy::F16),
	ty::SimplifiedType::Float(ty::FloatTy::F32),
	ty::SimplifiedType::Float(ty::FloatTy::F64),
	ty::SimplifiedType::Float(ty::FloatTy::F128),
	];

[chenyukang]

@lcnr
I updated the code in commit:
https://github.com/rust-lang/rust/compare/995c11894fdabe1c630694254de756f82389c6cf..112d833ea5c72f89078069ffc5d10da5b1adf2ca

I'm thinking do we need to delay_as_bug, since if we already returned Err(NonAsmTypeReason::Invalid(ty)), there will always an error reported error[E0084]: unsupported representation for ...

[chenyukang]

Ok, span_delay_bug seems checking the whether there is already an error before this point.

[chenyukang]

@rustbot ready

[lcnr]

@bors delegate+

[bors]

✌️ @chenyukang, you can now approve this pull request!

If @lcnr told you to "r=me" after making some further change, please make that change, then do @bors r=@lcnr

[chenyukang]

@bors r=Kivooeo,lcnr

[bors]

📌 Commit df57c32 has been approved by Kivooeo,lcnr

It is now in the queue for this repository.

[chenyukang]

@bors try jobs=test-various

[rust-bors]

💔 Test for 2c4f26b failed: CI. Failed jobs:

• try - test-various (web logs, extended logs)

[chenyukang]

@bors try jobs=test-various

[rust-bors]

💔 Test for 5ec32cc failed: CI. Failed jobs:

• try - test-various (web logs, extended logs)

[chenyukang]

@bors try jobs=test-various

[rust-bors]

☀️ Try build successful (CI)
Build commit: 9d98235 (9d98235200f597b8afa69e59002efc894f14891b, parent: 7a72c5459dd58f81b0e1a0e5436d145485889375)

[chenyukang]

finally it's passed, I added //@ needs-asm-support in the testcase.
@bors r=Kivooeo,lcnr

[bors]

📌 Commit 1610851 has been approved by Kivooeo,lcnr

It is now in the queue for this repository.

[bors]

⌛ Testing commit 1610851 with merge 5d9fe54...

[Zalathar]

Yielding to enclosing rollup.

@bors retry

[bors]

⌛ Testing commit 1610851 with merge c8551d3...