mir: prohibit projection into scalable vec by davidtwco · Pull Request #160642 · rust-lang/rust

davidtwco · 2026-08-06T14:15:30Z

Fixes #160580. Preventing projections into scalable vectors is an oversight from the initial implementation and something we should fix.

I'm surprised it caused a stdarch CI failure as reported by #160580, as nothing in rustc or stdarch seems to have changed that would have caused that to start happening as far as I can tell. This likely won't fix that stdarch CI failure if it keeps happening, because if there is a projection coming from somewhere then that needs to be fixed - nevertheless, preventing them as in this patch is the right thing to do.

I've tested this against the stdarch CI locally.

rustbot · 2026-08-06T14:15:34Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

stdarch is developed in its own repository. If possible, consider making this change to rust-lang/stdarch instead.

cc @Amanieu, @folkertdev, @sayantn

rustbot · 2026-08-06T14:15:37Z

r? @TaKO8Ki

rustbot has assigned @TaKO8Ki.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: compiler
compiler expanded to 75 candidates
Random selection from 16 candidates

davidtwco · 2026-08-06T14:15:40Z

r? @folkertdev

oli-obk · 2026-08-06T15:27:54Z

+//@ compile-flags: --target aarch64-unknown-linux-gnu -Copt-level=0
+//@ check-fail
+//@ needs-llvm-components: aarch64
+//@ only-aarch64


is the --target and needs-llvm-components necessary when it's already restricted to aarch64?

View changes since the review

going in the other direction, I think this can be a minicore test?

is the --target and needs-llvm-components necessary when it's already restricted to aarch64?

are you suggesting to remove both? (if you have a test with a --target, tidy will require needs-llvm-components)

But combining //@ only-aarch64 with compile-flags: --target aarch64-unknown-linux-gnu doesn't really make sense I think?

Anyhow, this should be a minicore test so it run everywhere.

Removed --target and needs-llvm-components, added minicore

Oh, sorry, I meant to keep --target and needs-llvm-components in combination with minicore, so that this test runs even on my x86_64 machine. The logic here isn't os-specific, so defaulting to aarch64-unknown-linux-gnu should be fine. It's the only-aarch64 that should go.

workingjubilee · 2026-08-06T19:08:33Z

cc @scottmcm Since you worked on prohibiting similar projections in the past.

davidtwco · 2026-08-07T09:00:32Z

cc @scottmcm Since you worked on prohibiting similar projections in the past.

I looked at #143833 while doing this - the rustc_mir_transform/src/validate.rs change is the same, not strictly necessary in my patch but gives a more deliberate ICE than the previous one as a fallback, but I didn't think the rustc_codegen_ssa/src/mir/operand.rs change was relevant here. ~~I went further than that patch with the rustc_hir_typeck change to give a nicer error than the MIR validation one.~~

scottmcm · 2026-08-07T09:03:36Z


+#[derive(Diagnostic)]
+#[diag("cannot project into scalable vector type `{$ty}`")]
+pub(crate) struct ScalableVectorFieldAccess<'tcx> {


Are you expecting scalable vectors to be something that people can mess up like this outside of the library? We intentionally just ICE under rust-lang/compiler-team#620 for the misuses of repr(simd).

(The tricky cases were things that didn't have a great place in the code to point at.)

View changes since the review

Ah, that makes sense, I hadn't considered that the visibility errors would prevent field access normally, so this was really only for direct uses of rustc_scalable_vector, so the MIR validator error is sufficient - removed the typeck error.

scottmcm · 2026-08-07T09:04:49Z

                        }

-                        if adt_def.repr().simd() {
+                        if adt_def.repr().simd() || adt_def.repr().scalable() {


Would it worth having a negative test that mir-opt SRoA doesn't try to explode one of these, or similar?

View changes since the review

I've added one now

folkertdev

Thanks, r=me when CI is green.

View changes since this review

folkertdev · 2026-08-07T13:52:13Z

Hmm i've been running into this too. Tidy already lints on tests having --target without an llvm component, maybe it can also lint on whether the target is available with gcc and error when it's not and suggest to ignore gcc.

folkertdev · 2026-08-07T20:42:55Z

@bors r+

rust-bors · 2026-08-07T20:42:59Z

📌 Commit 0e878d6 has been approved by folkertdev

It is now in the queue for this repository.

…folkertdev mir: prohibit projection into scalable vec Fixes rust-lang#160580. Preventing projections into scalable vectors is an oversight from the initial implementation and something we should fix. I'm surprised it caused a stdarch CI failure as reported by rust-lang#160580, as nothing in rustc or stdarch seems to have changed that would have caused that to start happening as far as I can tell. This likely won't fix that stdarch CI failure if it keeps happening, because if there is a projection coming from somewhere then that needs to be fixed - nevertheless, preventing them as in this patch is the right thing to do. I've tested this against the stdarch CI locally.

Rollup of 5 pull requests Successful merges: - #160634 (miri subtree update) - #160642 (mir: prohibit projection into scalable vec) - #160303 (rustc_parse: A few cleanups to expression parsing next to attributes) - #160429 (tidy: Update Python version requirements to 3.10) - #160543 (Default `RawOsError` to `i16` for 16-bit targets)

jhpratt · 2026-08-08T07:09:04Z

+extern crate minicore;
+
+#[rustc_scalable_vector(4)]
+pub struct Sv(f32);


This needs to silence a lint.

@bors r- #160735 (comment)

---- [ui] tests/ui/scalable-vectors/project-into-field-extern.rs stdout ---- error: auxiliary build of /Users/runner/work/rust/rust/tests/ui/scalable-vectors/auxiliary/simple.rs failed to compile: status: exit status: 1 command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2/bin/rustc" "/Users/runner/work/rust/rust/tests/ui/scalable-vectors/auxiliary/simple.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/Users/runner/.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/Users/runner/work/rust/rust/vendor" "--sysroot" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/stage2" "--target=aarch64-apple-darwin" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/Users/runner/work/rust/rust/build/aarch64-apple-darwin/native/rust-test-helpers" "-Cpanic=abort" "-Cforce-unwind-tables=yes" "-Copt-level=0" "--crate-type" "dylib" "-L" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary" "--extern" "minicore=/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/libminicore.rlib" stdout: none --- stderr ------------------------------- warning: field `0` is never read ##[warning] --> /Users/runner/work/rust/rust/tests/ui/scalable-vectors/auxiliary/simple.rs:13:15 | LL | pub struct Sv(f32); | -- ^^^ | | | field in this struct | = help: consider removing this field = note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default error: linking with `cc` failed: exit status: 1 | = note: "cc" "-Wl,-exported_symbols_list" "-Wl,/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary/rustcnDOBCi/list" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary/rustcnDOBCi/symbols.o" "<1 object files omitted>" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary/rustcnDOBCi/rmeta.o" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/libminicore.rlib" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-L" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/native/rust-test-helpers" "-L" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary" "-o" "/Users/runner/work/rust/rust/build/aarch64-apple-darwin/test/ui/scalable-vectors/project-into-field-extern/auxiliary/libsimple.dylib" "-Wl,-dead_strip" "-dynamiclib" "-Wl,-install_name" "-Wl,@rpath/libsimple.dylib" "-nodefaultlibs" = note: some arguments are omitted. use `--verbose` to show all linker arguments = note: Undefined symbols for architecture arm64: "dyld_stub_binder", referenced from: <initial-undefines> ld: symbol(s) not found for architecture arm64 clang: error: linker command failed with exit code 1 (use -v to see invocation) error: aborting due to 1 previous error; 1 warning emitted ------------------------------------------

View changes since the review

rust-bors · 2026-08-08T07:09:11Z

This pull request was unapproved.

This PR was contained in a rollup (#160735), which was unapproved.

View changes since this unapproval

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 6, 2026

rustbot assigned TaKO8Ki Aug 6, 2026

rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 6, 2026

rustbot assigned folkertdev and unassigned TaKO8Ki Aug 6, 2026

davidtwco mentioned this pull request Aug 6, 2026

Tracking Issue for Scalable Vectors #145052

Open

24 tasks

oli-obk reviewed Aug 6, 2026

View reviewed changes

folkertdev reviewed Aug 6, 2026

View reviewed changes

Comment thread library/stdarch/crates/core_arch/src/aarch64/sve/mod.rs

Comment thread compiler/rustc_hir_typeck/src/expr.rs Outdated

davidtwco force-pushed the sve-field-projection branch from 303387d to 168f22f Compare August 7, 2026 08:55

scottmcm reviewed Aug 7, 2026

View reviewed changes

davidtwco force-pushed the sve-field-projection branch from 168f22f to c1f9520 Compare August 7, 2026 11:54

davidtwco changed the title ~~hir_typeck: prohibit projection into scalable vec~~ mir: prohibit projection into scalable vec Aug 7, 2026

davidtwco force-pushed the sve-field-projection branch from c1f9520 to ae4a53f Compare August 7, 2026 11:58

folkertdev approved these changes Aug 7, 2026

View reviewed changes

This comment was marked as resolved.

Sign in to view

davidtwco force-pushed the sve-field-projection branch from ae4a53f to 8574222 Compare August 7, 2026 12:39

This comment has been minimized.

Sign in to view

mir: prohibit projection into scalable vec

0e878d6

davidtwco force-pushed the sve-field-projection branch from 8574222 to 0e878d6 Compare August 7, 2026 14:59

rust-bors Bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Aug 7, 2026

rust-bors Bot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 7, 2026

jhpratt mentioned this pull request Aug 8, 2026

Rollup of 5 pull requests #160735

Closed

jhpratt reviewed Aug 8, 2026

View reviewed changes

rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 8, 2026

Uh oh!

Uh oh!

Conversation

davidtwco commented Aug 6, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Aug 6, 2026

Uh oh!

rustbot commented Aug 6, 2026

Uh oh!

davidtwco commented Aug 6, 2026

Uh oh!

oli-obk Aug 6, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

workingjubilee commented Aug 6, 2026

Uh oh!

davidtwco commented Aug 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

scottmcm Aug 7, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

scottmcm Aug 7, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

folkertdev left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

This comment was marked as resolved.

This comment has been minimized.

folkertdev commented Aug 7, 2026

Uh oh!

folkertdev commented Aug 7, 2026

Uh oh!

rust-bors Bot commented Aug 7, 2026

Uh oh!

jhpratt Aug 8, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

rust-bors Bot commented Aug 8, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

10 participants

davidtwco commented Aug 6, 2026 •

edited by rustbot

Loading

oli-obk Aug 6, 2026 •

edited by rustbot

Loading

davidtwco commented Aug 7, 2026 •

edited

Loading

scottmcm Aug 7, 2026 •

edited by rustbot

Loading

scottmcm Aug 7, 2026 •

edited by rustbot

Loading

folkertdev left a comment •

edited by rustbot

Loading

jhpratt Aug 8, 2026 •

edited by rustbot

Loading