Jonathan Brouwer d7c812cb57 Rollup merge of #146900 - taiki-e:avr-target-feature, r=workingjubilee ...

Add avr_target_feature

This adds the following unstable target features (tracking issue: https://github.com/rust-lang/rust/issues/146889):

- The following two are particularly important for properly supporting inline assembly:
  - `tinyencoding`: AVR has devices that reduce the number of registers, similar to RISC-V's RV32E. This feature is necessary to support inline assembly in such devices. (see also https://github.com/rust-lang/rust/pull/146901)
  - `lowbytefirst`: AVR's memory access is per 8-bit, and when writing 16-bit ports, the bytes must be written in a specific order. This order depends on devices, making this feature necessary to write proper inline assembly for such use cases. (see also https://github.com/llvm/llvm-project/commit/2a528760bf20004066effcf8f91fedaabd261903)
- The followings help recognizing whether specific instructions are available:
  - `addsubiw`
  - `break`
  - `eijmpcall`
  - `elpm`
  - `elpmx`
  - `ijmpcall`
  - `jmpcall`
  - `lpm`
  - `lpmx`
  - `movw`
  - `mul`
  - `rmw`
  - `spm`
  - `spmx`

  Of these, all except `addsubiw`, `break`, `ijmpcall`, `lpm`, `rmw`, `spm`, and `spmx` have [corresponding conditional codes in avr-libc](https://github.com/search?q=repo%3Aavrdudes%2Favr-libc+%2F__AVR_HAVE_%2F&type=code&p=1). LLVM also has `des` feature, but I excluded it from this PR because [DES](https://en.wikipedia.org/wiki/Data_Encryption_Standard) is insecure.

- Report future-incompatible warning (https://github.com/rust-lang/rust/issues/116344) for -C target-feature=-sram and -C target-cpu=<device_without_sram> cases because SRAM is minimum requirement for non-assembly language in both avr-gcc and LLVM.
  - See https://github.com/rust-lang/rust/pull/146900#issuecomment-3323558005 for details.

LLVM also has `smallstack`, `wrappingrjmp`, and `memmappedregs` features, but I skipped them because they didn't seem to belong to either of the above categories, but I might have missed something.

(The feature names are match with [definitions in LLVM](https://github.com/llvm/llvm-project/blob/llvmorg-21.1.0/llvm/lib/Target/AVR/AVRDevices.td).)

cc @Patryk27 @Rahix
r? workingjubilee

@rustbot label +O-AVR +A-target-feature

2026-02-07 09:41:06 +01:00

..

src

Rollup merge of #146900 - taiki-e:avr-target-feature, r=workingjubilee

2026-02-07 09:41:06 +01:00

Cargo.toml

parser/lexer: bump to Unicode 17, use faster unicode-ident

2025-12-27 11:20:24 +01:00