Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` by scottmcm · Pull Request #158899 · rust-lang/rust

scottmcm · 2026-07-07T07:45:18Z

There seems to be no reason to have this flag at all, as anything that wants it should just adjust the https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/place/struct.PlaceValue.html#structfield.align instead.

r? codegen

rustbot · 2026-07-07T07:45:20Z

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

cc @antoyo, @GuillaumeGomez

scottmcm · 2026-07-07T07:47:10Z

-pub unsafe fn unaligned_volatile_store(a: *mut u8, b: u8) {
-    // CHECK: store volatile


Note that this test was essentially useless, since

It didn't actually test the alignment used in the store, and

It used u8 which always has alignment 1 even if you don't use unaligned.

So I expanded them to actually test things.

View changes since the review

scottmcm · 2026-07-07T07:49:23Z

+    // Note that only the store side is unaligned; the load from the argument is aligned.
+
+    // CHECK-NOT: memcpy
+    // CHECK: call void @llvm.memcpy{{.+}}(ptr align 1 %a, ptr align 2 %b, {{i16|i32|i64}} 14, i1 true)


A volatile memcpy is not actually a good way to do this, but it's not a regression at least since it's what this emits in nightly today (https://rust.godbolt.org/z/josnWhGa6).

(See danlehmann/bitfield#136 for more -- it's looking at this problem that had me looking at volatile stores at all. I'll make another PR after this one to work on that problem.)

View changes since the review

saethlin · 2026-07-09T00:27:28Z

@bors r+ rollup=iffy (Scott's codegen tests are usually good but codegen tests are famous for failing due to surprise target sensitivity)

rust-bors · 2026-07-09T00:27:32Z

📌 Commit 9116f7d has been approved by saethlin

It is now in the queue for this repository.

scottmcm · 2026-07-09T05:08:03Z

I appreciate your confidence in me, but also 100% agree with marking my codegen tests as iffy. I've had plenty of problems too 🙃

…saethlin Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` Fixes rust-lang#158897 There seems to be no reason to have this flag at all, as anything that wants it should just adjust the https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/place/struct.PlaceValue.html#structfield.align instead. r? codegen

…uwer Rollup of 17 pull requests Successful merges: - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #157153 (allow `Allocator`s to be used as `#[global_allocator]`s) - #158535 (Support `#[track_caller]` on EII declarations) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places")

…saethlin Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` Fixes rust-lang#158897 There seems to be no reason to have this flag at all, as anything that wants it should just adjust the https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/place/struct.PlaceValue.html#structfield.align instead. r? codegen

…uwer Rollup of 21 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #155429 (Support `u128`/`i128` c-variadic arguments) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159005 (Use `as_lang_item` instead of repeatedly matching)

…saethlin Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` Fixes rust-lang#158897 There seems to be no reason to have this flag at all, as anything that wants it should just adjust the https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/place/struct.PlaceValue.html#structfield.align instead. r? codegen

…uwer Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes)

jhpratt · 2026-07-09T23:56:29Z

I presume this is the cause of #159037 (comment), as I don't see any other PRs in that rollup that could possibly cause over 4,000 tests to fail.

@bors r-

@bors try jobs=dist-i586-gnu-i586-i686-musl

rust-bors · 2026-07-09T23:56:35Z

This pull request was unapproved.

This PR was contained in a rollup (#159037), which was unapproved.

View changes since this unapproval

Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` try-job: dist-i586-gnu-i586-i686-musl

scottmcm · 2026-07-10T00:04:24Z

Oh, joy, i586 :/

scottmcm · 2026-07-10T00:06:15Z

@jhpratt Hmm, #158510 looks potentially interesting?

Enable static_position_independent_executables on all gnu and musl targets

If the failing job is both gnu and musl...

jhpratt · 2026-07-10T00:08:16Z

Good catch, I didn't see there was another codegen PR. I'll exclude both from rollups for the time being.

rust-bors · 2026-07-10T00:54:49Z

💔 Test for 421a606 failed: CI. Failed job:

try - dist-i586-gnu-i586-i686-musl (web logs, enhanced plaintext logs)

rust-log-analyzer · 2026-07-10T00:54:54Z

The job dist-i586-gnu-i586-i686-musl failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

test [debuginfo-gdb] tests/debuginfo/zst-interferes-with-prologue.rs ... ok

failures:

---- [debuginfo-gdb] tests/debuginfo/function-call.rs stdout ----
NOTE: compiletest thinks it is using GDB version 12001000
------gdb stdout------------------------------
GNU gdb (Ubuntu 12.1-0ubuntu1~22.04.2) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word".
Breakpoint 1 at 0x804f592: file /checkout/tests/debuginfo/function-call.rs, line 36.

Breakpoint 1, function_call::main () at /checkout/tests/debuginfo/function-call.rs:36
36     zzz(); // #break

------gdb stderr------------------------------
/checkout/obj/build/x86_64-unknown-linux-gnu/test/debuginfo/function-call.gdb/function-call.debugger.script:11: Error in sourced command file:
Couldn't write extended state status: Bad address.

------------------------------------------

error: gdb failed to execute
status: exit status: 1
command: PYTHONPATH="/checkout/src/etc" "/usr/bin/gdb" "-quiet" "-batch" "-nx" "-command=/checkout/obj/build/x86_64-unknown-linux-gnu/test/debuginfo/function-call.gdb/function-call.debugger.script"
--- stdout -------------------------------
GNU gdb (Ubuntu 12.1-0ubuntu1~22.04.2) 12.1
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word".
Breakpoint 1 at 0x804f592: file /checkout/tests/debuginfo/function-call.rs, line 36.

Breakpoint 1, function_call::main () at /checkout/tests/debuginfo/function-call.rs:36
36     zzz(); // #break
------------------------------------------
--- stderr -------------------------------
/checkout/obj/build/x86_64-unknown-linux-gnu/test/debuginfo/function-call.gdb/function-call.debugger.script:11: Error in sourced command file:
Couldn't write extended state status: Bad address.
------------------------------------------

scottmcm · 2026-07-10T04:04:04Z

That's not the "every UI test" failure, so let's see if it's transient...

@bors try jobs=dist-i586-gnu-i586-i686-musl

Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` try-job: dist-i586-gnu-i586-i686-musl

rust-bors · 2026-07-10T05:49:26Z

☀️ Try build successful (CI)
Build commit: 066e1fb (066e1fbbb183e71b867e3251fcbb722464c3b3b4)
Base parent: d465559 (d465559281ebfb5b586913285f4d40f9b518b729)

scottmcm · 2026-07-10T05:56:54Z

Re-approving since the try job above confirms this wasn't the source of the rollup issue

@bors r=saethlin

rust-bors · 2026-07-10T05:56:58Z

📌 Commit 9116f7d has been approved by saethlin

It is now in the queue for this repository.

Rollup of 7 pull requests Successful merges: - #155429 (Support `u128`/`i128` c-variadic arguments) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #158640 (Handle nested inline consts in const argument checks) - #158866 ([perf] Add explicit `Iterator::count` impl for `ChunkBy`.) - #158912 (Introduce new bootstrap config section for PGO configuration) - #159040 (Print step stack trace when bootstrap panics) - #159056 (Print a loud error if the configured LLDB cannot be found)

Rollup merge of #158899 - scottmcm:better-volatile-store, r=saethlin Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` Fixes #158897 There seems to be no reason to have this flag at all, as anything that wants it should just adjust the https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/mir/place/struct.PlaceValue.html#structfield.align instead. r? codegen

Fix unaligned_volatile_store by removing MemFlags::UNALIGNED

9116f7d

rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 7, 2026

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rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Jul 7, 2026

scottmcm commented Jul 7, 2026

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Rollup of 17 pull requests #159007

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Rollup of 18 pull requests #159013

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Rollup of 21 pull requests #159020

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Rollup of 21 pull requests #159024

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Rollup of 24 pull requests #159037

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Auto merge of #158899 - scottmcm:better-volatile-store, r=<try>

421a606

Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` try-job: dist-i586-gnu-i586-i686-musl

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rust-bors Bot pushed a commit that referenced this pull request Jul 10, 2026

Auto merge of #158899 - scottmcm:better-volatile-store, r=<try>

066e1fb

Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED` try-job: dist-i586-gnu-i586-i686-musl

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 10, 2026

jhpratt mentioned this pull request Jul 10, 2026

Rollup of 7 pull requests #159057

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rust-bors Bot merged commit 731d820 into rust-lang:main Jul 10, 2026
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rustbot added this to the 1.99.0 milestone Jul 10, 2026

		pub unsafe fn unaligned_volatile_store(a: *mut u8, b: u8) {
		// CHECK: store volatile

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