high memory requirement during monomorphization

I noticed this while fuzzing because rustc would crash after hitting the memory limit inside the sandbox We need around 1.5 gb of memory during monomorphization here it seems. Next solver does not help.

I tried this code: rustc file.rs -Ztime-passes -Clink-dead-code

struct Foo {
    bar: dyn for<'r> Fn(usize, &'r dyn Fn(
            &dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(u32))))))))),
        ))
}

fn main() {
}

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rustc --version --verbose:

rustc 1.80.0-nightly (8c127df75 2024-05-16)
binary: rustc
commit-hash: 8c127df75fde3d5ad8ef9af664962a7676288b52
commit-date: 2024-05-16
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.4

Backtrace

``` rustc ice.rs -Ztime-passes -Clink-dead-code time: 0.000; rss: 46MB -> 47MB ( +2MB) parse_crate time: 0.000; rss: 48MB -> 49MB ( +1MB) setup_global_ctxt time: 0.000; rss: 50MB -> 50MB ( +1MB) crate_injection time: 0.002; rss: 50MB -> 63MB ( +12MB) expand_crate time: 0.002; rss: 50MB -> 63MB ( +12MB) macro_expand_crate time: 0.000; rss: 63MB -> 63MB ( +0MB) AST_validation time: 0.000; rss: 63MB -> 63MB ( +0MB) finalize_imports time: 0.000; rss: 63MB -> 67MB ( +4MB) finalize_macro_resolutions time: 0.000; rss: 67MB -> 67MB ( +0MB) late_resolve_crate time: 0.000; rss: 67MB -> 67MB ( +0MB) resolve_check_unused time: 0.000; rss: 67MB -> 67MB ( +0MB) resolve_postprocess time: 0.001; rss: 63MB -> 67MB ( +5MB) resolve_crate time: 0.000; rss: 68MB -> 68MB ( +0MB) complete_gated_feature_checking time: 0.000; rss: 68MB -> 69MB ( +2MB) looking_for_entry_point time: 0.000; rss: 70MB -> 71MB ( +0MB) unused_lib_feature_checking time: 0.000; rss: 68MB -> 71MB ( +3MB) misc_checking_1 time: 0.001; rss: 71MB -> 78MB ( +7MB) coherence_checking time: 0.001; rss: 71MB -> 79MB ( +8MB) type_check_crate time: 0.000; rss: 79MB -> 81MB ( +2MB) MIR_borrow_checking time: 0.000; rss: 81MB -> 82MB ( +1MB) MIR_effect_checking warning: struct `Foo` is never constructed --> ice.rs:1:8 | 1 | struct Foo { | ^^^ | = note: `#[warn(dead_code)]` on by default time: 0.000; rss: 86MB -> 86MB ( +0MB) module_lints time: 0.000; rss: 86MB -> 86MB ( +0MB) lint_checking time: 0.002; rss: 82MB -> 86MB ( +4MB) misc_checking_3 time: 0.000; rss: 86MB -> 87MB ( +1MB) monomorphization_collector_root_collections time: 5.850; rss: 87MB -> 1537MB (+1450MB) monomorphization_collector_graph_walk time: 0.000; rss: 1537MB -> 1538MB ( +1MB) partition_and_assert_distinct_symbols time: 0.000; rss: 1538MB -> 1541MB ( +3MB) write_allocator_module time: 0.001; rss: 1547MB -> 1557MB ( +9MB) codegen_to_LLVM_IR time: 5.853; rss: 86MB -> 1557MB (+1471MB) codegen_crate time: 0.000; rss: 1557MB -> 1557MB ( +0MB) serialize_dep_graph time: 0.023; rss: 1557MB -> 1279MB ( -277MB) LLVM_passes time: 0.078; rss: 1557MB -> 209MB (-1349MB) free_global_ctxt time: 0.051; rss: 209MB -> 209MB ( +0MB) run_linker time: 0.052; rss: 209MB -> 209MB ( +0MB) link_binary time: 0.052; rss: 209MB -> 209MB ( +0MB) link_crate time: 0.052; rss: 209MB -> 209MB ( +0MB) link warning: 1 warning emitted time: 5.999; rss: 32MB -> 102MB ( +70MB) total ```

rust-lang / rust

high memory requirement during monomorphization #125212

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