UI tests `linkage-detect-local-generated-name-collision.rs` and `linkage-detect-extern-generated-name-collision.rs` trigger LLVM asserts when compiled with CGUs = 1

[the8472]

This was discovered in #81942 (comment) which lowers the default CGU count to 1. The tests were modified to explicitly request 16CGUs to make them pass, but the underlying issue remains.

This should be reproducible by setting assertions = true in config.toml and running ./x.py test --stage 1 src/test/ui on commit 01c682043d3632dab421c263b8a2263b08b01bab (base commit aef1140) or by adding // compile-flags: -Ccodegen-units=1 to the tests.

---- [ui] ui/linkage-attr/linkage-detect-local-generated-name-collision.rs stdout ----

error: Error: expected failure status (Some(1)) but received status None.
status: signal: 6 (core dumped)
command: "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustc" "/home/the8472/workspace/rust/src/test/ui/linkage-attr/linkage-detect-local-generated-name-collision.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zemit-future-incompat-report" "-C" "prefer-dynamic" "--out-dir" "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/test/ui/linkage-attr/linkage-detect-local-generated-name-collision" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-Clink-args=-fuse-ld=lld" "-Clink-arg=-Wl,--threads=1" "-Ccodegen-units=2" "-L" "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/test/ui/linkage-attr/linkage-detect-local-generated-name-collision/auxiliary"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
rustc: /home/the8472/workspace/rust/src/llvm-project/llvm/include/llvm/Support/Casting.h:269: typename llvm::cast_retty<X, Y*>::ret_type llvm::cast(Y*) [with X = llvm::GlobalValue; Y = llvm::Value; typename llvm::cast_retty<X, Y*>::ret_type = llvm::GlobalValue*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

------------------------------------------


---- [ui] ui/linkage-attr/linkage-detect-extern-generated-name-collision.rs stdout ----

error: Error: expected failure status (Some(1)) but received status None.
status: signal: 6 (core dumped)
command: "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/stage1/bin/rustc" "/home/the8472/workspace/rust/src/test/ui/linkage-attr/linkage-detect-extern-generated-name-collision.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zemit-future-incompat-report" "-C" "prefer-dynamic" "--out-dir" "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/test/ui/linkage-attr/linkage-detect-extern-generated-name-collision" "-A" "unused" "-Crpath" "-O" "-Cdebuginfo=0" "-Zunstable-options" "-Lnative=/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-Clink-args=-fuse-ld=lld" "-Clink-arg=-Wl,--threads=1" "-Ccodegen-units=2" "-L" "/home/the8472/workspace/rust/build/x86_64-unknown-linux-gnu/test/ui/linkage-attr/linkage-detect-extern-generated-name-collision/auxiliary"
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
rustc: /home/the8472/workspace/rust/src/llvm-project/llvm/include/llvm/Support/Casting.h:269: typename llvm::cast_retty<X, Y*>::ret_type llvm::cast(Y*) [with X = llvm::GlobalValue; Y = llvm::Value; typename llvm::cast_retty<X, Y*>::ret_type = llvm::GlobalValue*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

------------------------------------------



failures:
    [ui] ui/linkage-attr/linkage-detect-extern-generated-name-collision.rs
    [ui] ui/linkage-attr/linkage-detect-local-generated-name-collision.rs

[Qi-Hu]

This issue is fixed by commit df552b3. The error is caused by the bitcasting in the function getOrInsertGlobal, which is called by function LLVMRustGetOrInsertGlobal. It happens when there is a name collision and CGUs is set to 1. The commit rewrote the function LLVMRustGetOrInsertGlobal without bitcasting and fixed this issue.

[Qi-Hu]

This issue is fixed by commit df552b3. The error is caused by the bitcasting in the function getOrInsertGlobal, which is called by function LLVMRustGetOrInsertGlobal. It happens when there is a name collision and CGUs is set to 1. The commit rewrote the function LLVMRustGetOrInsertGlobal without bitcasting and fixed this issue.

If there's no objection, I propose closing this issue.

[Enselic]

Triage: No objections were raised, let's close.