Allow building LLVM DLL with MSVC

[Zoxc]

This allows building a LLVM DLL with MSVC using the LLVM_BUILD_LLVM_DYLIB_VIS option which limit symbols exported by the shared library.

This PR as written would also change exported symbols for other targets, which may affect LLVM plugins if the required symbols are not exported.

[Zoxc]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[rust-bors]

💔 Test for 3415beb failed: CI. Failed job:

• try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

[Zoxc]

@bors try @rust-timer queue

[rust-timer]

This pull request is already queued and waiting for a try build to finish.

[rust-bors]

💔 Test for 3ca981e failed: CI. Failed job:

• try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

[rust-log-analyzer]

The job dist-x86_64-linux-quick failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 1`
##[endgroup]
[2026-07-29T02:14:50.332Z INFO  opt_dist::timer] Section `Stage 1 (Rustc + rustdoc PGO)` starts
[2026-07-29T02:14:50.332Z INFO  opt_dist::timer] Section `Stage 1 (Rustc + rustdoc PGO) > Build PGO instrumented rustc and LLVM` starts
[2026-07-29T02:14:50.332Z INFO  opt_dist::exec] Executing `RUST_BACKTRACE=full python3 /checkout/x.py build --target x86_64-unknown-linux-gnu --host x86_64-unknown-linux-gnu --stage 2 library/std --set rust.llvm-bitcode-linker=false --set build.extended=false --set rust.codegen-backends=['llvm'] --set rust.deny-warnings=false rustdoc cargo --set pgo.rustc.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set pgo.cargo.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set pgo.rustdoc.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set llvm.thin-lto=false --set llvm.link-shared=true [at /checkout/obj]`
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.06s
##[endgroup]
[TIMING:start] compile::Assemble { target_compiler: Compiler { stage: 2, host: x86_64-unknown-linux-gnu, forced_compiler: false } }
[TIMING:start] builder::Libdir { compiler: Compiler { stage: 2, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu }
---
[ 94%] Linking CXX executable ../../bin/llvm-offload-binary
[ 94%] Building CXX object tools/llvm-profgen/CMakeFiles/llvm-profgen.dir/ProfiledBinary.cpp.o
[ 94%] Building CXX object tools/llvm-profgen/CMakeFiles/llvm-profgen.dir/CSPreInliner.cpp.o
[ 94%] Building CXX object tools/llvm-rc/CMakeFiles/llvm-rc.dir/ResourceScriptCppFilter.cpp.o
CMakeFiles/llvm-ir2vec.dir/llvm-ir2vec.cpp.o: In function `llvm::ir2vec::IR2VecTool::writeEmbeddingsToStream(llvm::Function const&, llvm::raw_ostream&, llvm::EmbeddingLevel) const':
llvm-ir2vec.cpp:(.text._ZNK4llvm6ir2vec10IR2VecTool23writeEmbeddingsToStreamERKNS_8FunctionERNS_11raw_ostreamENS_14EmbeddingLevelE+0x2c9): undefined reference to `llvm::ir2vec::Embedder::computeEmbeddings() const'
llvm-ir2vec.cpp:(.text._ZNK4llvm6ir2vec10IR2VecTool23writeEmbeddingsToStreamERKNS_8FunctionERNS_11raw_ostreamENS_14EmbeddingLevelE+0x474): undefined reference to `llvm::ir2vec::Embedder::computeEmbeddings(llvm::BasicBlock const&) const'
CMakeFiles/llvm-ir2vec.dir/llvm-ir2vec.cpp.o: In function `llvm::mir2vec::MIR2VecTool::generateTriplets(llvm::MachineFunction const&) const':
llvm-ir2vec.cpp:(.text._ZNK4llvm7mir2vec11MIR2VecTool16generateTripletsERKNS_15MachineFunctionE+0x2f2): undefined reference to `llvm::mir2vec::MIRVocabulary::getCommonOperandIndex(llvm::MachineOperand::MachineOperandType) const'
[ 94%] Built target llvm-extract
[ 94%] Building CXX object tools/llvm-rc/CMakeFiles/llvm-rc.dir/ResourceScriptParser.cpp.o
[ 94%] Built target llvm-isel-fuzzer
[ 94%] Linking CXX executable ../../bin/llvm-opt-report
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[2]: *** [bin/llvm-ir2vec] Error 1
gmake[1]: *** [tools/llvm-ir2vec/CMakeFiles/llvm-ir2vec.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....
[ 94%] Building CXX object tools/llvm-profgen/CMakeFiles/llvm-profgen.dir/ProfileGenerator.cpp.o
[ 94%] Building CXX object tools/llvm-rc/CMakeFiles/llvm-rc.dir/ResourceScriptStmt.cpp.o
[ 94%] Building CXX object tools/llvm-readobj/CMakeFiles/llvm-readobj.dir/COFFDumper.cpp.o
[ 94%] Linking CXX executable ../../bin/llvm-mca
---
   9:     0x55a071bc7402 - std[230c7218466d7ceb]::panicking::default_hook::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:292:27
  10:     0x55a071be394c - std[230c7218466d7ceb]::panicking::default_hook
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:319:9
  11:     0x55a070d333b9 - <alloc[20281b059bda2f70]::boxed::Box<dyn for<'a, 'b> core[8ec35bcd8078f253]::ops::function::Fn<(&'a std[230c7218466d7ceb]::panic::PanicHookInfo<'b>,), Output = ()> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::marker::Send> as core[8ec35bcd8078f253]::ops::function::Fn<(&std[230c7218466d7ceb]::panic::PanicHookInfo,)>>::call
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/alloc/src/boxed.rs:2333:9
  12:     0x55a070d2dae0 - bootstrap[86ed21b2d5261d0]::main::{closure#0}
                               at /checkout/src/bootstrap/src/bin/main.rs:48:9
  13:     0x55a071be3cb2 - <alloc[20281b059bda2f70]::boxed::Box<dyn for<'a, 'b> core[8ec35bcd8078f253]::ops::function::Fn<(&'a std[230c7218466d7ceb]::panic::PanicHookInfo<'b>,), Output = ()> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::marker::Send> as core[8ec35bcd8078f253]::ops::function::Fn<(&std[230c7218466d7ceb]::panic::PanicHookInfo,)>>::call
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/alloc/src/boxed.rs:2333:9
  14:     0x55a071be3cb2 - std[230c7218466d7ceb]::panicking::panic_with_hook
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:823:13
  15:     0x55a071bc74b2 - std[230c7218466d7ceb]::panicking::panic_handler::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:688:13
  16:     0x55a071bbe579 - std[230c7218466d7ceb]::sys::backtrace::__rust_end_short_backtrace::<std[230c7218466d7ceb]::panicking::panic_handler::{closure#0}, !>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/backtrace.rs:182:18
  17:     0x55a071bc851d - __rustc[a25a212e9fab2cd3]::rust_begin_unwind
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:679:5
  18:     0x55a070d28bbc - core[8ec35bcd8078f253]::panicking::panic_fmt
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/panicking.rs:80:14
  19:     0x55a071700e27 - cmake[eebe24415ec307ea]::fail
  20:     0x55a071700ab3 - cmake[eebe24415ec307ea]::run
  21:     0x55a071706aeb - <cmake[eebe24415ec307ea]::Config>::build
  22:     0x55a07113cde7 - <bootstrap[8c00cf1cfb06d8c]::core::build_steps::llvm::Llvm as bootstrap[8c00cf1cfb06d8c]::core::builder::CommandLineStep>::run
                               at /checkout/src/bootstrap/src/core/build_steps/llvm.rs:563:13
  23:     0x55a0711374f9 - <bootstrap[8c00cf1cfb06d8c]::core::build_steps::llvm::Llvm as bootstrap[8c00cf1cfb06d8c]::core::builder::Step>::run
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:131:9
  24:     0x55a0714c3104 - <bootstrap[8c00cf1cfb06d8c]::core::builder::Builder>::ensure::<bootstrap[8c00cf1cfb06d8c]::core::build_steps::llvm::Llvm>
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:1662:36
  25:     0x55a070f4f783 - <bootstrap[8c00cf1cfb06d8c]::core::build_steps::compile::Assemble as bootstrap[8c00cf1cfb06d8c]::core::builder::CommandLineStep>::run
                               at /checkout/src/bootstrap/src/core/build_steps/compile.rs:2114:69
  26:     0x55a070f2a2b7 - <bootstrap[8c00cf1cfb06d8c]::core::build_steps::compile::Assemble as bootstrap[8c00cf1cfb06d8c]::core::builder::Step>::run
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:131:9
  27:     0x55a071584d57 - <bootstrap[8c00cf1cfb06d8c]::core::builder::Builder>::ensure::<bootstrap[8c00cf1cfb06d8c]::core::build_steps::compile::Assemble>
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:1662:36
  28:     0x55a071624080 - <bootstrap[8c00cf1cfb06d8c]::core::builder::Builder>::compiler
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:1217:14
  29:     0x55a070f47905 - <bootstrap[8c00cf1cfb06d8c]::core::build_steps::compile::Std as bootstrap[8c00cf1cfb06d8c]::core::builder::CommandLineStep>::make_run
                               at /checkout/src/bootstrap/src/core/build_steps/compile.rs:142:41
  30:     0x55a0716194ea - <bootstrap[8c00cf1cfb06d8c]::core::builder::CommandLineStepDescription>::maybe_run
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:502:13
  31:     0x55a0712c248a - bootstrap[8c00cf1cfb06d8c]::core::builder::cli_paths::match_paths_to_steps_and_run
                               at /checkout/src/bootstrap/src/core/builder/cli_paths.rs:233:18
  32:     0x55a071623016 - <bootstrap[8c00cf1cfb06d8c]::core::builder::Builder>::run_step_descriptions
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:1189:9
  33:     0x55a07161c742 - <bootstrap[8c00cf1cfb06d8c]::core::builder::Builder>::execute_cli
                               at /checkout/src/bootstrap/src/core/builder/mod.rs:1168:14
  34:     0x55a070f087cc - <bootstrap[8c00cf1cfb06d8c]::Build>::build
                               at /checkout/src/bootstrap/src/lib.rs:802:25
  35:     0x55a070d2ffdc - bootstrap[86ed21b2d5261d0]::main
                               at /checkout/src/bootstrap/src/bin/main.rs:157:11
  36:     0x55a070d333e3 - <fn() as core[8ec35bcd8078f253]::ops::function::FnOnce<()>>::call_once
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/ops/function.rs:250:5
  37:     0x55a070d2a1d6 - std[230c7218466d7ceb]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/backtrace.rs:166:18
  38:     0x55a070d2d509 - std[230c7218466d7ceb]::rt::lang_start::<()>::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:206:18
  39:     0x55a071be2357 - <&dyn core[8ec35bcd8078f253]::ops::function::Fn<(), Output = i32> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::panic::unwind_safe::RefUnwindSafe as core[8ec35bcd8078f253]::ops::function::FnOnce<()>>::call_once
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/ops/function.rs:287:21
  40:     0x55a071be2357 - std[230c7218466d7ceb]::panicking::catch_unwind::do_call::<&dyn core[8ec35bcd8078f253]::ops::function::Fn<(), Output = i32> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::panic::unwind_safe::RefUnwindSafe, i32>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:576:43
  41:     0x55a071be2357 - std[230c7218466d7ceb]::panicking::catch_unwind::<i32, &dyn core[8ec35bcd8078f253]::ops::function::Fn<(), Output = i32> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::panic::unwind_safe::RefUnwindSafe>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:544:19
  42:     0x55a071be2357 - std[230c7218466d7ceb]::panic::catch_unwind::<&dyn core[8ec35bcd8078f253]::ops::function::Fn<(), Output = i32> + core[8ec35bcd8078f253]::marker::Sync + core[8ec35bcd8078f253]::panic::unwind_safe::RefUnwindSafe, i32>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panic.rs:359:14
  43:     0x55a071be2357 - std[230c7218466d7ceb]::rt::lang_start_internal::{closure#0}
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:175:24
  44:     0x55a071be2357 - std[230c7218466d7ceb]::panicking::catch_unwind::do_call::<std[230c7218466d7ceb]::rt::lang_start_internal::{closure#0}, isize>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:576:43
  45:     0x55a071be2357 - std[230c7218466d7ceb]::panicking::catch_unwind::<isize, std[230c7218466d7ceb]::rt::lang_start_internal::{closure#0}>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:544:19
  46:     0x55a071be2357 - std[230c7218466d7ceb]::panic::catch_unwind::<std[230c7218466d7ceb]::rt::lang_start_internal::{closure#0}, isize>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panic.rs:359:14
  47:     0x55a071be2357 - std[230c7218466d7ceb]::rt::lang_start_internal
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:171:5
  48:     0x55a070d29ff1 - std[230c7218466d7ceb]::rt::lang_start::<()>
                               at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:205:5
---
[2026-07-29T02:16:47.038Z INFO  opt_dist::utils] Free disk space: 1.28 TiB out of total 2.51 TiB (48.86% used)
Error: Optimized build pipeline has failed

Caused by:
    Command RUST_BACKTRACE=full python3 /checkout/x.py build --target x86_64-unknown-linux-gnu --host x86_64-unknown-linux-gnu --stage 2 library/std --set rust.llvm-bitcode-linker=false --set build.extended=false --set rust.codegen-backends=['llvm'] --set rust.deny-warnings=false rustdoc cargo --set pgo.rustc.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set pgo.cargo.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set pgo.rustdoc.generate="/tmp/tmp-multistage/opt-artifacts/rustc-pgo" --set llvm.thin-lto=false --set llvm.link-shared=true [at /checkout/obj] has failed with exit code Some(1)

Stack backtrace:
   0: <anyhow::Error>::msg::<alloc::string::String>
             at /rust/deps/anyhow-1.0.102/src/backtrace.rs:10:14
   1: <opt_dist::exec::CmdBuilder>::run
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/exec.rs:81:17
   2: <opt_dist::exec::Bootstrap>::run
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/exec.rs:251:18
   3: opt_dist::execute_pipeline::{closure#1}::{closure#0}
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/main.rs:265:25
   4: <opt_dist::timer::TimerSection>::section::<opt_dist::execute_pipeline::{closure#1}::{closure#0}, ()>
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/timer.rs:111:22
   5: opt_dist::execute_pipeline::{closure#1}
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/main.rs:246:19
   6: <opt_dist::timer::TimerSection>::section::<opt_dist::execute_pipeline::{closure#1}, (opt_dist::training::RustcPGOProfile, opt_dist::training::RustdocPGOProfile)>
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/timer.rs:111:22
   7: opt_dist::execute_pipeline
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/main.rs:243:15
   8: opt_dist::main
             at /rustc/3ca981ef0caa77b61484753888229beae18dfe52/src/tools/opt-dist/src/main.rs:516:18
   9: <fn() -> core::result::Result<(), anyhow::Error> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/ops/function.rs:250:5
  10: std::sys::backtrace::__rust_begin_short_backtrace::<fn() -> core::result::Result<(), anyhow::Error>, core::result::Result<(), anyhow::Error>>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/sys/backtrace.rs:166:18
  11: std::rt::lang_start::<core::result::Result<(), anyhow::Error>>::{closure#0}
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:206:18
  12: <&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe as core::ops::function::FnOnce<()>>::call_once
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/core/src/ops/function.rs:287:21
  13: std::panicking::catch_unwind::do_call::<&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe, i32>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:576:43
  14: std::panicking::catch_unwind::<i32, &dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:544:19
  15: std::panic::catch_unwind::<&dyn core::ops::function::Fn<(), Output = i32> + core::marker::Sync + core::panic::unwind_safe::RefUnwindSafe, i32>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panic.rs:359:14
  16: std::rt::lang_start_internal::{closure#0}
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/rt.rs:175:24
  17: std::panicking::catch_unwind::do_call::<std::rt::lang_start_internal::{closure#0}, isize>
             at /rustc/08d5b675a9b2abdca5e2fe4eabe0e07bbda15d49/library/std/src/panicking.rs:576:43