ICE `inlining failed in call to ‘always_inline’ func... | rust-lang/rustc_codegen_gcc

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snippet:

//@compile-flags: -Zcodegen-backend=gcc -Clink-dead-code=true -Copt-level=3
fn main() {
    let mut bytes = vec![];
    let id = 1234u32;
    let port_number = 8080u16;
    let some_random_string = "".to_string();
    bytes.splice(0..4, id.to_be_bytes());
    bytes.splice(25..27, port_number.to_be_bytes());
    some_random_string.as_bytes().to_vec();
    println!("bytes: {:?}, len: {}", bytes, bytes.len())
}

Version information

rustc 1.95.0-nightly (a18e6d9d1 2026-01-24)
binary: rustc
commit-hash: a18e6d9d1473d9b25581dd04bef6c7577999631c
commit-date: 2026-01-24
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zcodegen-backend=gcc -Clink-dead-code=true -Copt-level=3

Program output

libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvXs2D_NtNtCsjXZVF46obq5_4core5slice4iterINtB6_4IterhENtNtNtNtBa_4iter6traits10exact_size17ExactSizeIterator3lenCs3Ktur3hQz7J_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs2C_NtNtCsjXZVF46obq5_4core5slice4iterINtB6_4IterhE10make_sliceCs3Ktur3hQz7J_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvXs2D_NtNtCsjXZVF46obq5_4core5slice4iterINtB6_4IterhENtNtNtNtBa_4iter6traits10exact_size17ExactSizeIterator3lenCs3Ktur3hQz7J_4mvce’: function body not available
libgccjit.so: error: : inlining failed in call to ‘always_inline’ ‘_RNvMs2C_NtNtCsjXZVF46obq5_4core5slice4iterINtB6_4IterhE10make_sliceCs3Ktur3hQz7J_4mvce’: function body not available
error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-m64" "/tmp/icemaker_global_tempdir.O3K6xjHgMH4d/rustc_testrunner_tmpdir_reporting.RIyO3bTgJ9ub/rustcFOFs9D/symbols.o" "<3 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/tmp/icemaker_global_tempdir.O3K6xjHgMH4d/rustc_testrunner_tmpdir_reporting.RIyO3bTgJ9ub/rustcFOFs9D/raw-dylibs" "-B<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/bin/gcc-ld" "-fuse-ld=lld" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "outputfile" "-pie" "-Wl,-z,relro,-z,now" "-Wl,-O1" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: rust-lld: error: cannot open outputfile.mvce.2bac8b0cd4d5b33d-cgu.1.rcgu.o: No such file or directory
          collect2: error: ld returned 1 exit status
          

error: aborting due to 1 previous error

Start with the Rust reproducer in /tmp/gcc/a.rs and run it using -Zcodegen-backend=gcc, -Clink-dead-code=true, and -Copt-level=3. Trace the generated object files and libgccjit linker errors to identify why the always_inline function body is unavailable; done means the reproducer links successfully without the ICE.

Written by the indexing model from the issue text.

ICE `inlining failed in call to ‘always_inline’ function body not available` (`-Copt-level=(2..)`

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