Segfault while compiling rustc_codegen_spirv #29

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1. schell

   added

   bugSomething isn't workingSomething isn't working

   on Oct 10, 2024
2. schell commented on Oct 11, 2024

   

   schell

   on Oct 11, 2024

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   Here's how far I got with lldb

   First I set up a command source file lldb_env_setup.lldb to hold all the env vars and cli options:

   settings set target.env-vars CARGO=/Users/schell/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/cargo
   settings set target.env-vars CARGO_CRATE_NAME=rustc_codegen_spirv
   settings set target.env-vars CARGO_MANIFEST_DIR=/Users/schell/code/rust-gpu/crates/rustc_codegen_spirv
   settings set target.env-vars CARGO_PKG_AUTHORS='rust-gpu developers:Embark <opensource@embark-studios.com>'
   settings set target.env-vars CARGO_PKG_DESCRIPTION='SPIR-V code generator backend for rustc'
   settings set target.env-vars CARGO_PKG_HOMEPAGE=''
   settings set target.env-vars CARGO_PKG_LICENSE='MIT OR Apache-2.0'
   settings set target.env-vars CARGO_PKG_LICENSE_FILE=''
   settings set target.env-vars CARGO_PKG_NAME=rustc_codegen_spirv
   settings set target.env-vars CARGO_PKG_README=README.md
   settings set target.env-vars CARGO_PKG_REPOSITORY='https://github.com/rust-gpu/rust-gpu'
   settings set target.env-vars CARGO_PKG_RUST_VERSION=''
   settings set target.env-vars CARGO_PKG_VERSION=0.9.0
   settings set target.env-vars CARGO_PKG_VERSION_MAJOR=0
   settings set target.env-vars CARGO_PKG_VERSION_MINOR=9
   settings set target.env-vars CARGO_PKG_VERSION_PATCH=0
   settings set target.env-vars CARGO_PKG_VERSION_PRE=''
   settings set target.env-vars CARGO_PRIMARY_PACKAGE=1
   settings set target.env-vars CARGO_RUSTC_CURRENT_DIR=/Users/schell/code/rust-gpu
   settings set target.env-vars DYLD_FALLBACK_LIBRARY_PATH='/Users/schell/code/rust-gpu/target/debug/deps:/Users/schell/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/lib:/Users/schell/lib:/usr/local/lib:/usr/lib'
   settings set target.env-vars OUT_DIR=/Users/schell/code/rust-gpu/target/debug/build/rustc_codegen_spirv-6bf5e31abd8107a7/out
   
   target create /Users/schell/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/rustc
   
   process launch --  --crate-name rustc_codegen_spirv --edition=2021 crates/rustc_codegen_spirv/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=202 --crate-type dylib --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked --cfg 'feature="default"' --cfg 'feature="use-compiled-tools"' -C metadata=c01b1899eb4284a6 --out-dir /Users/schell/code/rust-gpu/target/debug/deps -C incremental=/Users/schell/code/rust-gpu/target/debug/incremental -L dependency=/Users/schell/code/rust-gpu/target/debug/deps --extern ar=/Users/schell/code/rust-gpu/target/debug/deps/libar-e3ad7146ff683a59.rlib --extern either=/Users/schell/code/rust-gpu/target/debug/deps/libeither-b182a76c8248f318.rlib --extern hashbrown=/Users/schell/code/rust-gpu/target/debug/deps/libhashbrown-6c72dab48672ca38.rlib --extern indexmap=/Users/schell/code/rust-gpu/target/debug/deps/libindexmap-6bda499f2b061353.rlib --extern itertools=/Users/schell/code/rust-gpu/target/debug/deps/libitertools-91ee06ba4bd713a5.rlib --extern lazy_static=/Users/schell/code/rust-gpu/target/debug/deps/liblazy_static-4bc53d643ec30e40.rlib --extern libc=/Users/schell/code/rust-gpu/target/debug/deps/liblibc-e18c03c84dd0c02a.rlib --extern num_traits=/Users/schell/code/rust-gpu/target/debug/deps/libnum_traits-1d980cb5a4875be2.rlib --extern once_cell=/Users/schell/code/rust-gpu/target/debug/deps/libonce_cell-771796d3f5371d07.rlib --extern regex=/Users/schell/code/rust-gpu/target/debug/deps/libregex-9c2651fc8523aa8a.rlib --extern rspirv=/Users/schell/code/rust-gpu/target/debug/deps/librspirv-9e368a3016245c72.rlib --extern rustc_demangle=/Users/schell/code/rust-gpu/target/debug/deps/librustc_demangle-61ad1dd711dcb489.rlib --extern rustc_codegen_spirv_types=/Users/schell/code/rust-gpu/target/debug/deps/librustc_codegen_spirv_types-3d976a4394529b29.rlib --extern sanitize_filename=/Users/schell/code/rust-gpu/target/debug/deps/libsanitize_filename-c0f3b53de5315d3c.rlib --extern smallvec=/Users/schell/code/rust-gpu/target/debug/deps/libsmallvec-d36e0788f4d18c2f.rlib --extern spirt=/Users/schell/code/rust-gpu/target/debug/deps/libspirt-f6c8c35ab9a8f5c2.rlib --extern spirv_tools=/Users/schell/code/rust-gpu/target/debug/deps/libspirv_tools-554835daf8d19504.rlib -Dunsafe_code '-Wclippy::all' '-Wclippy::await_holding_lock' '-Wclippy::char_lit_as_u8' '-Wclippy::checked_conversions' '-Wclippy::dbg_macro' '-Wclippy::debug_assert_with_mut_call' '-Wclippy::doc_markdown' '-Wclippy::empty_enum' '-Wclippy::enum_glob_use' '-Wclippy::exit' '-Wclippy::expl_impl_clone_on_copy' '-Wclippy::explicit_deref_methods' '-Wclippy::explicit_into_iter_loop' '-Wclippy::fallible_impl_from' '-Wclippy::filter_map_next' '-Wclippy::flat_map_option' '-Wclippy::float_cmp_const' '-Wclippy::fn_params_excessive_bools' '-Wclippy::from_iter_instead_of_collect' '-Wclippy::if_let_mutex' '-Wclippy::implicit_clone' '-Wclippy::imprecise_flops' '-Wclippy::inefficient_to_string' '-Wclippy::invalid_upcast_comparisons' '-Wclippy::large_digit_groups' '-Wclippy::large_stack_arrays' '-Wclippy::large_types_passed_by_value' '-Wclippy::let_unit_value' '-Wclippy::linkedlist' '-Wclippy::lossy_float_literal' '-Wclippy::macro_use_imports' '-Wclippy::manual_ok_or' '-Wclippy::map_err_ignore' '-Wclippy::map_flatten' '-Wclippy::map_unwrap_or' '-Wclippy::match_on_vec_items' '-Wclippy::match_same_arms' '-Wclippy::match_wild_err_arm' '-Wclippy::match_wildcard_for_single_variants' '-Wclippy::mem_forget' '-Wclippy::mismatched_target_os' '-Wclippy::missing_enforced_import_renames' '-Wclippy::mut_mut' '-Wclippy::mutex_integer' '-Wclippy::needless_borrow' '-Wclippy::needless_continue' '-Wclippy::needless_for_each' '-Wclippy::option_option' '-Wclippy::path_buf_push_overwrite' '-Wclippy::ptr_as_ptr' '-Wclippy::rc_mutex' '-Wclippy::ref_option_ref' '-Wclippy::rest_pat_in_fully_bound_structs' '-Wclippy::same_functions_in_if_condition' '-Wclippy::semicolon_if_nothing_returned' '-Wclippy::single_match_else' '-Wclippy::string_add_assign' '-Wclippy::string_add' '-Wclippy::string_lit_as_bytes' '-Wclippy::string_to_string' '-Wclippy::todo' '-Wclippy::trait_duplication_in_bounds' '-Wclippy::unimplemented' '-Wclippy::unnested_or_patterns' '-Wclippy::unused_self' '-Wclippy::useless_transmute' '-Wclippy::verbose_file_reads' '-Wclippy::zero_sized_map_values' -Wfuture_incompatible -Wnonstandard_style -Wrust_2018_idioms -Aunsafe_code -L native=/Users/schell/code/rust-gpu/target/debug/build/spirv-tools-sys-d4c0736b4c5521a0/out
   

   Then I invoke lldb and do:

   command source lldb_env_setup.lldb
   

   Which then shows:

   Process 13821 launched: '/Users/schell/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/rustc' (arm64)
   {"$message_type":"artifact","artifact":"/Users/schell/code/rust-gpu/target/debug/deps/rustc_codegen_spirv.d","emit":"dep-info"}
   Process 13821 stopped
   * thread #8, name = 'opt 4zue6wczm9w1glco', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
       frame #0: 0x000000010cea5d04 librustc_driver-ca847c7e3a88e281.dylib`llvm::AArch64RegisterBankInfo::isLoadFromFPType(llvm::MachineInstr const&) const + 212
   librustc_driver-ca847c7e3a88e281.dylib`llvm::AArch64RegisterBankInfo::isLoadFromFPType:
   ->  0x10cea5d04 <+212>: ldr    x9, [x8]
       0x10cea5d08 <+216>: ldrb   w8, [x9, #0x8]
       0x10cea5d0c <+220>: cmp    w8, #0x10
       0x10cea5d10 <+224>: ccmp   x9, #0x0, #0x4, eq
   Target 3: (rustc) stopped.
   
3. schell commented on Oct 11, 2024

   

   schell

   on Oct 11, 2024

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   It builds in --release! But it won't otherwise.

   👍React with 👍3Reacted by Utensil, Timur Tugushev and Marek Bernat
4. utensil commented on Oct 11, 2024

   

   utensil

   on Oct 11, 2024

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   I have the same issue, cargo run --release works for example runners/wgpu, but has the same error if not with --release.
5. LegNeato commented on Oct 11, 2024

   

   LegNeato

   on Oct 11, 2024

   Last edited by LegNeato

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   Interesting, CI only appears to check x86_64 on Mac:

   os: macOS-latest
   target: x86_64-apple-darwin
   

   Though the docs say latest is arm? 🤔

   https://docs.github.com/en/actions/using-github-hosted-runners/using-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories

   And it looks like CI only uses --release 😩
6. LegNeato commented on Oct 13, 2024

   

   LegNeato

   on Oct 13, 2024

   Last edited by LegNeato

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   I was able to update rust-gpu to nightly-2024-06-20 and this crash went away. It was still there under nightly-2024-05-20.

   Many of the tests fail with hacks to get around the alloca changes preventing us from updating (rust-lang/rust@f4426c1) but the compiling works at least which points to an old llvm or rustc issue unrelated to rust-gpu.
7. LegNeato commented on Oct 14, 2024

   

   LegNeato

   on Oct 14, 2024

   Last edited by eddyb

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   @eddyb found the cause:

   • rustc 1.78.0 segfault on MacOS / M1 rust-lang/rust#125053

   nightly-2024-05-21 has the fix

   👍React with 👍1Reacted by Utensil
8. eddyb commented on Oct 14, 2024

   

   eddyb

   on Oct 14, 2024

   Last edited by eddyb

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   Likely culprit: llvm/llvm-project@70579c9

   This leaves Feb 14th - May 20th as the range with the bug, i.e. between:

   • Update to LLVM 18 rust-lang/rust#120055
   • Update to LLVM 18.1.6 rust-lang/rust#125288

   Looking at the report (rust-lang/rust#125053), it is weirdly specific. I wonder if it's in code we control.

   * thread #8, name = 'opt 4zue6wczm9w1glco'

   @schell if you have the time, it might be useful to try to add -C save-temps and hopefully get access to the 4zue6wczm9w1glco codegen-unit before it's optimized.
9. schell commented on Oct 14, 2024

   

   schell

   on Oct 14, 2024

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   Nice sleuthing @eddyb and @LegNeato. I'll try it out when I can 🙇 .
10. eddyb commented on Oct 14, 2024

    

    eddyb

    on Oct 14, 2024

    Last edited by eddyb

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    Found a relatively low-effort way to inject lldb (doesn't even cause rebuilds!):

    $ echo '"$@" || (lldb -b -o "process launch" -- "$@" && exit 99)' > wrapper.sh
    $ chmod +x wrapper.sh
    $ RUSTC_WRAPPER=./wrapper.sh cargo rustc -p rustc_codegen_spirv --no-default-features --features use-installed-tools -- -C save-temps
       Compiling rustc_codegen_spirv v0.9.0 (/Users/eddyb/Code/rust-gpu/crates/rustc_codegen_spirv)
    /Users/eddyb/Code/rust-gpu/./wrapper.sh: line 1: 12630 Segmentation fault: 11  "$@"
    (lldb) target create "/Users/eddyb/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/rustc"
    Current executable set to '/Users/eddyb/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/rustc' (arm64).
    (lldb) settings set -- target.run-args  "--crate-name" "rustc_codegen_spirv" "--edition=2021" "crates/rustc_codegen_spirv/src/lib.rs" "--error-format=json" "--json=diagnostic-rendered-ansi,artifacts,future-incompat" "--diagnostic-width=147" "--crate-type" "dylib" "--emit=dep-info,link" "-C" "embed-bitcode=no" "-C" "debuginfo=2" "-C" "split-debuginfo=unpacked" "-C" "save-temps" "--cfg" "feature=\"use-installed-tools\"" "-C" "metadata=d3f81d8f7c25b8cf" "--out-dir" "/Users/eddyb/Code/rust-gpu/target/debug/deps" "-C" "incremental=/Users/eddyb/Code/rust-gpu/target/debug/incremental" "-L" "dependency=/Users/eddyb/Code/rust-gpu/target/debug/deps" "--extern" "ar=/Users/eddyb/Code/rust-gpu/target/debug/deps/libar-e3ad7146ff683a59.rlib" "--extern" "either=/Users/eddyb/Code/rust-gpu/target/debug/deps/libeither-b182a76c8248f318.rlib" "--extern" "hashbrown=/Users/eddyb/Code/rust-gpu/target/debug/deps/libhashbrown-d17b05ac8765534d.rlib" "--extern" "indexmap=/Users/eddyb/Code/rust-gpu/target/debug/deps/libindexmap-5721173ffd4b737f.rlib" "--extern" "itertools=/Users/eddyb/Code/rust-gpu/target/debug/deps/libitertools-91ee06ba4bd713a5.rlib" "--extern" "lazy_static=/Users/eddyb/Code/rust-gpu/target/debug/deps/liblazy_static-4bc53d643ec30e40.rlib" "--extern" "libc=/Users/eddyb/Code/rust-gpu/target/debug/deps/liblibc-1fb46c3556945141.rlib" "--extern" "num_traits=/Users/eddyb/Code/rust-gpu/target/debug/deps/libnum_traits-893caca608ed540b.rlib" "--extern" "once_cell=/Users/eddyb/Code/rust-gpu/target/debug/deps/libonce_cell-e9b1da7b0201a63a.rlib" "--extern" "regex=/Users/eddyb/Code/rust-gpu/target/debug/deps/libregex-b32f0d5f03e3e84d.rlib" "--extern" "rspirv=/Users/eddyb/Code/rust-gpu/target/debug/deps/librspirv-99fce9813432e2d2.rlib" "--extern" "rustc_demangle=/Users/eddyb/Code/rust-gpu/target/debug/deps/librustc_demangle-61ad1dd711dcb489.rlib" "--extern" "rustc_codegen_spirv_types=/Users/eddyb/Code/rust-gpu/target/debug/deps/librustc_codegen_spirv_types-b835e0468acc55e4.rlib" "--extern" "sanitize_filename=/Users/eddyb/Code/rust-gpu/target/debug/deps/libsanitize_filename-86f3198c840fea75.rlib" "--extern" "smallvec=/Users/eddyb/Code/rust-gpu/target/debug/deps/libsmallvec-503084d070b4a84a.rlib" "--extern" "spirt=/Users/eddyb/Code/rust-gpu/target/debug/deps/libspirt-ce67463698cb406c.rlib" "--extern" "spirv_tools=/Users/eddyb/Code/rust-gpu/target/debug/deps/libspirv_tools-1edd2bdab4924908.rlib" "-Dunsafe_code" "-Wclippy::all" "-Wclippy::await_holding_lock" "-Wclippy::char_lit_as_u8" "-Wclippy::checked_conversions" "-Wclippy::dbg_macro" "-Wclippy::debug_assert_with_mut_call" "-Wclippy::doc_markdown" "-Wclippy::empty_enum" "-Wclippy::enum_glob_use" "-Wclippy::exit" "-Wclippy::expl_impl_clone_on_copy" "-Wclippy::explicit_deref_methods" "-Wclippy::explicit_into_iter_loop" "-Wclippy::fallible_impl_from" "-Wclippy::filter_map_next" "-Wclippy::flat_map_option" "-Wclippy::float_cmp_const" "-Wclippy::fn_params_excessive_bools" "-Wclippy::from_iter_instead_of_collect" "-Wclippy::if_let_mutex" "-Wclippy::implicit_clone" "-Wclippy::imprecise_flops" "-Wclippy::inefficient_to_string" "-Wclippy::invalid_upcast_comparisons" "-Wclippy::large_digit_groups" "-Wclippy::large_stack_arrays" "-Wclippy::large_types_passed_by_value" "-Wclippy::let_unit_value" "-Wclippy::linkedlist" "-Wclippy::lossy_float_literal" "-Wclippy::macro_use_imports" "-Wclippy::manual_ok_or" "-Wclippy::map_err_ignore" "-Wclippy::map_flatten" "-Wclippy::map_unwrap_or" "-Wclippy::match_on_vec_items" "-Wclippy::match_same_arms" "-Wclippy::match_wild_err_arm" "-Wclippy::match_wildcard_for_single_variants" "-Wclippy::mem_forget" "-Wclippy::mismatched_target_os" "-Wclippy::missing_enforced_import_renames" "-Wclippy::mut_mut" "-Wclippy::mutex_integer" "-Wclippy::needless_borrow" "-Wclippy::needless_continue" "-Wclippy::needless_for_each" "-Wclippy::option_option" "-Wclippy::path_buf_push_overwrite" "-Wclippy::ptr_as_ptr" "-Wclippy::rc_mutex" "-Wclippy::ref_option_ref" "-Wclippy::rest_pat_in_fully_bound_structs" "-Wclippy::same_functions_in_if_condition" "-Wclippy::semicolon_if_nothing_returned" "-Wclippy::single_match_else" "-Wclippy::string_add_assign" "-Wclippy::string_add" "-Wclippy::string_lit_as_bytes" "-Wclippy::string_to_string" "-Wclippy::todo" "-Wclippy::trait_duplication_in_bounds" "-Wclippy::unimplemented" "-Wclippy::unnested_or_patterns" "-Wclippy::unused_self" "-Wclippy::useless_transmute" "-Wclippy::verbose_file_reads" "-Wclippy::zero_sized_map_values" "-Wfuture_incompatible" "-Wnonstandard_style" "-Wrust_2018_idioms" "-Aunsafe_code"
    (lldb) process launch
    {"$message_type":"diagnostic","message":"failed to connect to jobserver from environment variable `CARGO_MAKEFLAGS=\"-j --jobserver-fds=8,9 --jobserver-auth=8,9\"`: cannot open file descriptor 8 from the jobserver environment variable value: Bad file descriptor (os error 9)","code":null,"level":"warning","spans":[],"children":[{"message":"the build environment is likely misconfigured","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"\u001b[0m\u001b[1m\u001b[33mwarning\u001b[0m\u001b[0m\u001b[1m: failed to connect to jobserver from environment variable `CARGO_MAKEFLAGS=\"-j --jobserver-fds=8,9 --jobserver-auth=8,9\"`: cannot open file descriptor 8 from the jobserver environment variable value: Bad file descriptor (os error 9)\u001b[0m\n\u001b[0m  \u001b[0m\u001b[0m\u001b[1m\u001b[38;5;12m|\u001b[0m\n\u001b[0m  \u001b[0m\u001b[0m\u001b[1m\u001b[38;5;12m= \u001b[0m\u001b[0m\u001b[1mnote\u001b[0m\u001b[0m: the build environment is likely misconfigured\u001b[0m\n\n"}
    {"$message_type":"artifact","artifact":"/Users/eddyb/Code/rust-gpu/target/debug/deps/rustc_codegen_spirv.d","emit":"dep-info"}
    Process 12653 stopped
    * thread #8, name = 'opt 4q5ivfep7qt5yoow', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
        frame #0: 0x000000010d2edd04 librustc_driver-ca847c7e3a88e281.dylib`llvm::AArch64RegisterBankInfo::isLoadFromFPType(llvm::MachineInstr const&) const + 212
    librustc_driver-ca847c7e3a88e281.dylib`llvm::AArch64RegisterBankInfo::isLoadFromFPType:
    ->  0x10d2edd04 <+212>: ldr    x9, [x8]
        0x10d2edd08 <+216>: ldrb   w8, [x9, #0x8]
        0x10d2edd0c <+220>: cmp    w8, #0x10
        0x10d2edd10 <+224>: ccmp   x9, #0x0, #0x4, eq
    Target 0: (rustc) stopped.
    Process 12653 launched: '/Users/eddyb/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/bin/rustc' (arm64)
    error: could not compile `rustc_codegen_spirv` (lib)

    Then:

    $ env $(rustc --print=sysroot)/lib/rustlib/aarch64-apple-darwin/bin/llvm-dis \
      target/debug/deps/rustc_codegen_spirv.4q5ivfep7qt5yoow.rcgu.no-opt.bc
    $ rg '[^,{]( \{ )+\{\}, ' target/debug/deps/rustc_codegen_spirv.4q5ivfep7qt5yoow.rcgu.no-opt.ll
    12:@_RNvNvMsh_NtNtCsbqr1HCq8ilm_12rustc_middle2ty4listINtB7_7RawListupE5empty5EMPTY = external global { {}, i64, [7 x i64], [0 x {}] }
    $ cargo install rustfilt
    $ rg '[^,{]( \{ )+\{\}, ' target/debug/deps/rustc_codegen_spirv.4q5ivfep7qt5yoow.rcgu.no-opt.ll | rustfilt
    @<rustc_middle::ty::list::RawList<(), _>>::empty::EMPTY = external global { {}, i64, [7 x i64], [0 x {}] }

    (note the 4q5ivfep7qt5yoow I took from the crashing thread name!)

    Now, if it is that symbol, that's bad news because it's in rustc itself, i.e.:

    $ nm ~/.rustup/toolchains/nightly-2024-04-24-aarch64-apple-darwin/lib/librustc_driver-ca847c7e3a88e281.dylib \
      | rg _RNvNvMsh_NtNtCsbqr1HCq8ilm_12rustc_middle2ty4listINtB7_7RawListupE5empty5EMPTY
    000000000506c680 S __RNvNvMsh_NtNtCsbqr1HCq8ilm_12rustc_middle2ty4listINtB7_7RawListupE5empty5EMPTY

    Does this mean nobody on M1 could've contributed to rustc in rust-lang/rust? Or is this "unoptimized" mode so unlikely to be applied to rustc development? (Or am I looking at the wrong plausible cause)

    EDIT: the real culprit is a load from that global variable:

    $ rg 'load.*@_RNvNvMsh_NtNtCsbqr1HCq8ilm_12rustc_middle2ty4listINtB7_7RawListupE5empty5EMPTY' target/debug/deps/rustc_codegen_spirv.4q5ivfep7qt5yoow.rcgu.ll
    17832:  %119 = load i64, ptr @_RNvNvMsh_NtNtCsbqr1HCq8ilm_12rustc_middle2ty4listINtB7_7RawListupE5empty5EMPTY, align 8, !dbg !68816

    (not sure yet if we can avoid it, but optimizations simply replace it with 0...)

    👍React with 👍1Reacted by Utensil
11. LegNeato

    added

    fixed by forward porting

    on Nov 7, 2024
12. eddyb commented on Nov 27, 2024

    

    eddyb

    on Nov 27, 2024

    Last edited by eddyb

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    We have two options to deal with this:

    • detect the combination of aarch64 and debug mode and error explicitly
      • this should work even with just cfgs, (the bug happens while compiling rustc_codegen_spirv, but all the way down in LLVM, so e.g. compile_error! should still prevent it)
      • we could tell the user to use release mode, or if build scripts are involved (not sure if we can automatically detect that), add workspace-level Cargo.toml overrides like the ones we use
    • try to bypass rustc_codegen_ssa's MIR Return terminator codegen under the assumption that it's the only root cause
      • in theory, we could always support PassMode::Indirect, we've just ignored it
        (worst case, the inliner has to inline calls passing "out" pointers illegally)
      • to keep at least some things returned by-value we could use PassMode::Cast, when there's an obvious mapping to the [somewhat strange CastTarget` system](https://github.com/rust-lang/rust/blob/244da22fabd9fa677bbd0ac601a88e5ca6917526/compiler/rustc_target/src/abi/call/mod.rs#L190-L301)
        • if we get to lower multi-element Uniform (with integer/float elements) into vectors instead of structs, that might cover a lot of types, but we don't even get integer signedness
        • alternatively, we could "cheat" by making cast_backend_type(cast_ty) return a special placeholder (ignoring cast_ty's contents), which load+ret special-case to give the original type
      • we control everything else via store_arg/store_fn_arg/fn_decl_backend_type, so the function signatures can remain whatever we want them to be, at the SPIR-V level
      • to avoid PassMode::Cast insanity, we could "just" always use PassMode::Indirect, and pretend the signature has an extra pointer at the start (which is, instead, a local variable, that we can load on ret_void, to do the actual return)
    • vendor a fixed copy of rustc_codegen_ssa and/or build one on the user's machine, from the source code provided by the rustc-dev rustup component
      • since all the dependencies of any rustc_* crate should already have been supplied by rustc-dev, Cargo might not even be necessary
      • even a separate rustc invocation might be superfluous: we can, in theory, copy all the source files, patch them, then include them from rustc_codegen_spirv
      • even if this is the whackiest approach, it might prove useful long-term
        • _{oh dear lord that's our ticket to continuing to use alloca types
          (if we add a new method, there's only 2 callsites to patch: PlaceRef::alloca and some weird immediate-newtype-of-vector hack - also, PlaceRef::alloca gets type information to this day)}
          • EDIT: see Hack around blockers to update toolchain all the way to nightly-2024-11-22 (~1.84). #170
13. eddyb

    closed this as completedin #170on Dec 18, 2024