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Should generate llvm.threadlocal.address for TLS accesses #136044

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nikic opened this issue Jan 25, 2025 · 0 comments · May be fixed by #139385
Open

Should generate llvm.threadlocal.address for TLS accesses #136044

nikic opened this issue Jan 25, 2025 · 0 comments · May be fixed by #139385
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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-thread-locals Area: Thread local storage (TLS) C-bug Category: This is a bug. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@nikic
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nikic commented Jan 25, 2025

See https://llvm.org/docs/LangRef.html#llvm-threadlocal-address-intrinsic. Instead of directly accessing the global, the result of @llvm.threadlocal.address(ptr @g) should be accessed.

This is required for correctness when using LLVM coroutines (not relevant for Rust), but it should also improve codegen in some cases because it will allow CSE/LICM of the TLS address calculation.
@nikic nikic added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. C-bug Category: This is a bug. labels Jan 25, 2025
@rustbot rustbot added the needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. label Jan 25, 2025
@nikic nikic mentioned this issue Jan 25, 2025
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@jieyouxu jieyouxu added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-thread-locals Area: Thread local storage (TLS) and removed needs-triage This issue may need triage. Remove it if it has been sufficiently triaged. labels Jan 25, 2025
@joboet joboet linked a pull request Apr 4, 2025 that will close this issue
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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. A-thread-locals Area: Thread local storage (TLS) C-bug Category: This is a bug. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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rustc_codegen_llvm: use threadlocal.address intrinsic to access TLS joboet/rust
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