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Add avr_target_feature #146900

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359854d
Add avr_target_feature
taiki-e Jan 9, 2026
febe008
Require sram target feature on AVR
taiki-e Jan 15, 2026
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2 changes: 2 additions & 0 deletions compiler/rustc_feature/src/unstable.rs
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Expand Up @@ -373,6 +373,8 @@ declare_features! (
(unstable, async_for_loop, "1.77.0", Some(118898)),
/// Allows `async` trait bound modifier.
(unstable, async_trait_bounds, "1.85.0", Some(62290)),
/// Target features on avr.
(unstable, avr_target_feature, "CURRENT_RUSTC_VERSION", Some(146889)),
/// Allows using Intel AVX10 target features and intrinsics
(unstable, avx10_target_feature, "1.88.0", Some(138843)),
/// Target features on bpf.
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1 change: 1 addition & 0 deletions compiler/rustc_span/src/symbol.rs
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Expand Up @@ -568,6 +568,7 @@ symbols! {
automatically_derived,
available_externally,
avr,
avr_target_feature,
avx,
avx10_target_feature,
avx512_target_feature,
Expand Down
41 changes: 33 additions & 8 deletions compiler/rustc_target/src/target_features.rs
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Expand Up @@ -885,6 +885,28 @@ static M68K_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
// tidy-alphabetical-end
];

static AVR_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
// tidy-alphabetical-start
("addsubiw", Unstable(sym::avr_target_feature), &[]),
("break", Unstable(sym::avr_target_feature), &[]),
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@Patryk27 Patryk27 Sep 23, 2025 •
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nit: what about name collisions? 👀

The RFC doesn't seem to mention this, but I can see AVR's break (or other "generic" word like mul) accidentally colliding with another arch in future - on the other hand, keeping the mapping 1:1 with LLVM (FeatureBREAK in this case) is important as well, IMO.

Other than that LGTM.

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@taiki-e taiki-e Sep 24, 2025

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Target feature name collisions with other architectures are fine. (e.g., the aes target feature exists on x86/x86_64 (AES-NI) and arm/aarch64/arm64ec (FEAT_AES) respectively.)

("eijmpcall", Unstable(sym::avr_target_feature), &[]),
("elpm", Unstable(sym::avr_target_feature), &[]),
("elpmx", Unstable(sym::avr_target_feature), &[]),
("ijmpcall", Unstable(sym::avr_target_feature), &[]),
("jmpcall", Unstable(sym::avr_target_feature), &[]),
("lowbytefirst", Unstable(sym::avr_target_feature), &[]),
("lpm", Unstable(sym::avr_target_feature), &[]),
("lpmx", Unstable(sym::avr_target_feature), &[]),
("movw", Unstable(sym::avr_target_feature), &[]),
("mul", Unstable(sym::avr_target_feature), &[]),
("rmw", Unstable(sym::avr_target_feature), &[]),
("spm", Unstable(sym::avr_target_feature), &[]),
("spmx", Unstable(sym::avr_target_feature), &[]),
("sram", Forbidden { reason: "devices that have no SRAM are unsupported" }, &[]),
("tinyencoding", Unstable(sym::avr_target_feature), &[]),
// tidy-alphabetical-end
];

/// When rustdoc is running, provide a list of all known features so that all their respective
/// primitives may be documented.
///
Expand All @@ -906,6 +928,7 @@ pub fn all_rust_features() -> impl Iterator<Item = (&'static str, Stability)> {
.chain(IBMZ_FEATURES)
.chain(SPARC_FEATURES)
.chain(M68K_FEATURES)
.chain(AVR_FEATURES)
.cloned()
.map(|(f, s, _)| (f, s))
}
Expand Down Expand Up @@ -983,12 +1006,8 @@ impl Target {
Arch::S390x => IBMZ_FEATURES,
Arch::Sparc | Arch::Sparc64 => SPARC_FEATURES,
Arch::M68k => M68K_FEATURES,
Arch::AmdGpu
| Arch::Avr
| Arch::Msp430
| Arch::SpirV
| Arch::Xtensa
| Arch::Other(_) => &[],
Arch::Avr => AVR_FEATURES,
Arch::AmdGpu | Arch::Msp430 | Arch::SpirV | Arch::Xtensa | Arch::Other(_) => &[],
}
}

Expand All @@ -1010,11 +1029,11 @@ impl Target {
MIPS_FEATURES_FOR_CORRECT_FIXED_LENGTH_VECTOR_ABI
}
Arch::AmdGpu => AMDGPU_FEATURES_FOR_CORRECT_FIXED_LENGTH_VECTOR_ABI,
Arch::Nvptx64 | Arch::Bpf | Arch::M68k => &[], // no vector ABI
Arch::Nvptx64 | Arch::Bpf | Arch::M68k | Arch::Avr => &[], // no vector ABI
Arch::CSky => CSKY_FEATURES_FOR_CORRECT_FIXED_LENGTH_VECTOR_ABI,
// FIXME: for some tier3 targets, we are overly cautious and always give warnings
// when passing args in vector registers.
Arch::Avr | Arch::Msp430 | Arch::SpirV | Arch::Xtensa | Arch::Other(_) => &[],
Arch::Msp430 | Arch::SpirV | Arch::Xtensa | Arch::Other(_) => &[],
}
}

Expand Down Expand Up @@ -1211,6 +1230,12 @@ impl Target {
// because the vector and float registers overlap.
FeatureConstraints { required: &[], incompatible: &["soft-float"] }
}
Arch::Avr => {
// SRAM is minimum requirement for C/C++ in both avr-gcc and Clang,
// and backends of them only support assembly for devices have no SRAM.
// See the discussion in https://github.com/rust-lang/rust/pull/146900 for more.
FeatureConstraints { required: &["sram"], incompatible: &[] }
}
_ => NOTHING,
}
}
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2 changes: 2 additions & 0 deletions src/doc/rustc/src/platform-support/avr-none.md
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Expand Up @@ -68,6 +68,8 @@ the possible variants:

https://github.com/llvm/llvm-project/blob/093d4db2f3c874d4683fb01194b00dbb20e5c713/clang/lib/Basic/Targets/AVR.cpp#L32

Note that devices that have no SRAM are not supported, same as when compiling C/C++ programs with avr-gcc or Clang.

## Testing

You can use [`simavr`](https://github.com/buserror/simavr) to emulate the
Expand Down
12 changes: 12 additions & 0 deletions tests/ui/abi/avr-sram.disable_sram.stderr
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@@ -0,0 +1,12 @@
warning: target feature `sram` cannot be disabled with `-Ctarget-feature`: devices that have no SRAM are unsupported
|
= note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>

warning: target feature `sram` must be enabled to ensure that the ABI of the current target can be implemented correctly
|
= note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>

warning: 2 warnings emitted

7 changes: 7 additions & 0 deletions tests/ui/abi/avr-sram.no_sram.stderr
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@@ -0,0 +1,7 @@
warning: target feature `sram` must be enabled to ensure that the ABI of the current target can be implemented correctly
|
= note: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #116344 <https://github.com/rust-lang/rust/issues/116344>

warning: 1 warning emitted

19 changes: 19 additions & 0 deletions tests/ui/abi/avr-sram.rs
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@@ -0,0 +1,19 @@
//@ add-minicore
//@ revisions: has_sram no_sram disable_sram
//@ build-pass
//@[has_sram] compile-flags: --target avr-none -C target-cpu=atmega328p
//@[has_sram] needs-llvm-components: avr
//@[no_sram] compile-flags: --target avr-none -C target-cpu=attiny11
//@[no_sram] needs-llvm-components: avr
//@[disable_sram] compile-flags: --target avr-none -C target-cpu=atmega328p -C target-feature=-sram
//@[disable_sram] needs-llvm-components: avr
//@ ignore-backends: gcc
//[no_sram,disable_sram]~? WARN target feature `sram` must be enabled
//[disable_sram]~? WARN target feature `sram` cannot be disabled with `-Ctarget-feature`

#![feature(no_core)]
#![no_core]
#![crate_type = "lib"]

extern crate minicore;
use minicore::*;
16 changes: 16 additions & 0 deletions tests/ui/check-cfg/target_feature.stderr
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Expand Up @@ -14,6 +14,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`7e10`
`a`
`aclass`
`addsubiw`
`adx`
`aes`
`altivec`
Expand Down Expand Up @@ -57,6 +58,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`bf16`
`bmi1`
`bmi2`
`break`
`bti`
`bulk-memory`
`c`
Expand All @@ -83,6 +85,9 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`e2`
`ecv`
`edsp`
`eijmpcall`
`elpm`
`elpmx`
`elrw`
`enhanced-sort`
`ermsb`
Expand Down Expand Up @@ -134,6 +139,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`hvx-length128b`
`hwdiv`
`i8mm`
`ijmpcall`
`isa-68000`
`isa-68010`
`isa-68020`
Expand All @@ -142,6 +148,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`isa-68060`
`isa-68881`
`isa-68882`
`jmpcall`
`jsconv`
`kl`
`lahfsahf`
Expand All @@ -152,6 +159,9 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`ld-seq-sa`
`leoncasa`
`lor`
`lowbytefirst`
`lpm`
`lpmx`
`lse`
`lse128`
`lse2`
Expand All @@ -173,11 +183,13 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`mops`
`movbe`
`movrs`
`movw`
`mp`
`mp1e2`
`msa`
`msync`
`mte`
`mul`
`multivalue`
`mutable-globals`
`neon`
Expand Down Expand Up @@ -242,6 +254,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`reference-types`
`relax`
`relaxed-simd`
`rmw`
`rtm`
`rva23u64`
`sb`
Expand Down Expand Up @@ -294,6 +307,8 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`sme2p1`
`soft-float`
`spe`
`spm`
`spmx`
`ssbs`
`sse`
`sse2`
Expand All @@ -318,6 +333,7 @@ LL | cfg!(target_feature = "_UNEXPECTED_VALUE");
`tbm`
`thumb-mode`
`thumb2`
`tinyencoding`
`tme`
`transactional-execution`
`trust`
Expand Down
1 change: 1 addition & 0 deletions tests/ui/target-feature/gate.rs
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Expand Up @@ -20,6 +20,7 @@
// gate-test-sparc_target_feature
// gate-test-x87_target_feature
// gate-test-m68k_target_feature
// gate-test-avr_target_feature

#[target_feature(enable = "x87")]
//~^ ERROR: currently unstable
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2 changes: 1 addition & 1 deletion tests/ui/target-feature/gate.stderr
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@@ -1,5 +1,5 @@
error[E0658]: the target feature `x87` is currently unstable
--> $DIR/gate.rs:24:18
--> $DIR/gate.rs:25:18
|
LL | #[target_feature(enable = "x87")]
| ^^^^^^^^^^^^^^
Expand Down
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