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Rollup merge of #136170 - taiki-e:atomics-32, r=workingjubilee

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Reject unsound toggling of Arm atomics-32 target feature

This target feature has the same semantics as RISC-V `forced-atomics` target feature that already marked as Forbidden  (f5ed0cb217) and toggling it can cause ABI incompatibility.

2f348cb7ce/compiler/rustc_target/src/target_features.rs (L479-L483)

[Comment on feature definition in LLVM](7109f52197/llvm/lib/Target/ARM/ARMFeatures.td (L572-L574)) also says:

> Code built with this feature is not ABI-compatible with code built without this feature, if atomic variables are exposed across the ABI boundary.

r? `@workingjubilee` or `@RalfJung`

`@rustbot` label +O-Arm
This commit is contained in:
León Orell Valerian Liehr 2025-01-29 06:03:24 +01:00 • committed by GitHub
commit 0b1d717758
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5
compiler/rustc_target/src/target_features.rs
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@ -137,6 +137,11 @@ const ARM_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
// tidy-alphabetical-start // tidy-alphabetical-start
("aclass", Unstable(sym::arm_target_feature), &[]), ("aclass", Unstable(sym::arm_target_feature), &[]),
("aes", Unstable(sym::arm_target_feature), &["neon"]), ("aes", Unstable(sym::arm_target_feature), &["neon"]),
(
"atomics-32",
Stability::Forbidden { reason: "unsound because it changes the ABI of atomic operations" },
&[],
),
("crc", Unstable(sym::arm_target_feature), &[]), ("crc", Unstable(sym::arm_target_feature), &[]),
("d32", Unstable(sym::arm_target_feature), &[]), ("d32", Unstable(sym::arm_target_feature), &[]),
("dotprod", Unstable(sym::arm_target_feature), &["neon"]), ("dotprod", Unstable(sym::arm_target_feature), &["neon"]),