AVR: Compilation in --release mode fails with LLVM ERROR: Not supported instr

[mbuesch]

When compiling the following minimal AVR template in --release mode, the compiler aborts with an LLVM error

https://github.com/avr-rust/template-bin.git

(This is an empty template with an empty main that does nothing.)

$ cargo build --target avr-atmega328p.json -Z build-std=core --release                                          
   Compiling compiler_builtins v0.1.39                                                                                                                     
   Compiling core v0.0.0 (.../rust-unstable/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)                     
   Compiling rustc-std-workspace-core v1.99.0 (.../rust-unstable/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc
-std-workspace-core)                                                         
   Compiling avr-std-stub v1.0.2                                             
LLVM ERROR: Not supported instr: <MCInst 258 <MCOperand Reg:1> <MCOperand Imm:15> <MCOperand Reg:47>>                                                      
error: could not compile `compiler_builtins`                                 
                                                                             
To learn more, run the command again with --verbose.                                                                                                       
warning: build failed, waiting for other jobs to finish...                                                                                                 
error: build failed                               

In debug mode the build works correctly:

$ cargo build --target avr-atmega328p.json -Z build-std=core                                                    
   Compiling core v0.0.0 (.../rust-unstable/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)                     
   Compiling compiler_builtins v0.1.39                                       
   Compiling rustc-std-workspace-core v1.99.0 (.../rust-unstable/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc
-std-workspace-core)                                                                                                                                       
   Compiling avr-std-stub v1.0.2                                             
   Compiling template-bin v0.1.0 (.../avr-rust-template)                                                                                  
    Finished dev [unoptimized + debuginfo] target(s) in 14.61s   

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (8e54a2113 2021-02-13)
binary: rustc
commit-hash: 8e54a21139ae96a2aca3129100b057662e2799b9
commit-date: 2021-02-13
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 11.0.1

[Rynibami]

I’ve got the same problem. I am building my software based upon the AVR template "avr-atmega328p.json” which I called "avr-unknown-gnu-atmega2560.json”. This file looks mostly identical to the existing atmega’s on the web :

{
    "arch": "avr",
    "cpu": "atmega2560",
    "data-layout": "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8",
    "eh-frame-header": false,
    "env": "",
    "exe-suffix": ".elf",
    "executables": true,
    "is-builtin": true,
    "late-link-args": {
        "gcc": [
            "-lgcc"
        ]
    },
    "linker": "avr-gcc",
    "linker-flavor": "gcc",
    "linker-is-gnu": true,
    "llvm-target": "avr-unknown-unknown",
    "no-builtins": true,
    "os": "unknown",
    "pre-link-args": {
        "gcc": [
            "-mmcu=atmega2560",
            "-Wl,--as-needed"
        ]
    },
    "target-c-int-width": "16",
    "target-endian": "little",
    "target-pointer-width": "16",
    "vendor": "unknown"
}

I tried to build my project (which is just empty) on the nightly and stable versions, but I get the same type of error:

LLVM ERROR: Not supported instr: <MCInst 258 <MCOperand Reg:1> <MCOperand Imm:15> <MCOperand Reg:45>>
error: could not compile `compiler_builtins`

Caused by:
  process didn't exit successfully: `rustc --crate-name compiler_builtins /Users/***/.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.39/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C panic=abort -C embed-bitcode=no --cfg 'feature="compiler-builtins"' --cfg 'feature="core"' --cfg 'feature="default"' --cfg 'feature="rustc-dep-of-std"' -C metadata=358757d918a0ced2 -C extra-filename=-358757d918a0ced2 --out-dir /Users/***/ctrlr/target/avr-unknown-gnu-atmega2560/release/deps --target /Users/***/ctrlr/avr-unknown-gnu-atmega2560.json -Z force-unstable-if-unmarked -L dependency=/Users/***/ctrlr/target/avr-unknown-gnu-atmega2560/release/deps -L dependency=/Users/***/ctrlr/target/release/deps --extern core=/Users/***/ctrlr/target/avr-unknown-gnu-atmega2560/release/deps/librustc_std_workspace_core-0fe1efb82ffd1726.rmeta --cap-lints allow --cfg 'feature="unstable"'` (exit code: 101)

[Rahix]

This is caused by rust-lang/compiler-builtins#400. A fix is pending in LLVM, but not yet merged... In the meantime, you can use the nightly-2021-01-07 compiler version:

rustup toolchain install nightly-2021-01-07
cargo +nightly-2021-01-07 build

[LvInSaNevL]

@Rahix sorry to reopen this older issue but I'm seeing the same issues. I've tried like 3 different versions of the rust compiler, plus the current (1.55) version, and they all have the exact same issue?

[Rahix]

nightly-2021-01-07 is the last working version as of now. We're still blocked on a fix landing in LLVM which is pending review (see the compiler-builtins issue linked above).

[mbuesch]

Is there any plan to resolve this issue?

[agausmann]

@mbuesch They are working on fixing the underlying bug in LLVM - D114611

[mbuesch]

Thanks for the update, @agausmann