target: default to the medium code model on LoongArch targets #130266
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The Rust LoongArch targets have been using the default LLVM code model so far, which is "small" in LLVM-speak and "normal" in LoongArch-speak. As described in the "Code Model" section of LoongArch ELF psABI spec v20231219 [1], one can only make function calls as far as ±128MiB with the "normal" code model; this is insufficient for very large software containing Rust components that needs to be linked into the big text section, such as Chromium. Because: * we do not want to ask users to recompile std if they are to build such software, * objects compiled with larger code models can be linked with those with smaller code models without problems, and * the "medium" code model is comparable to the "small"/"normal" one performance-wise (same data access pattern; each function call becomes 2-insn long and indirect, but this may be relaxed back into the direct 1-insn form in a future LLVM version), but is able to perform function calls within ±128GiB, it is better to just switch the targets to the "medium" code model, which is also "medium" in LLVM-speak. [1]: https://github.com/loongson/la-abi-specs/blob/v2.30/laelf.adoc#code-models Co-authored-by: WANG Rui <wangrui@loongson.cn>
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rustbot has assigned @petrochenkov. Use |
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These commits modify compiler targets. |
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It's better to mention in the PR description the comment suggesting the reland for some more context. It really helps Git archaeology several years later according to my experience... |
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@bors r+ rollup |
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…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#129320 (Fix crash when labeling arguments for call_once and friends) - rust-lang#130266 (target: default to the medium code model on LoongArch targets) - rust-lang#130297 (Dataflow cleanups) - rust-lang#130299 (Add set_dcx to ParseSess) - rust-lang#130301 (some fixes for clashing_extern_declarations lint) - rust-lang#130305 (Clippy: consider msrv for const context for const_float_bits_conv) r? `@ghost` `@rustbot` modify labels: rollup
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…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#129320 (Fix crash when labeling arguments for call_once and friends) - rust-lang#130266 (target: default to the medium code model on LoongArch targets) - rust-lang#130297 (Dataflow cleanups) - rust-lang#130299 (Add set_dcx to ParseSess) - rust-lang#130301 (some fixes for clashing_extern_declarations lint) - rust-lang#130305 (Clippy: consider msrv for const context for const_float_bits_conv) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#130266 - heiher:loong-medium-cmodel, r=compiler-errors target: default to the medium code model on LoongArch targets The Rust LoongArch targets have been using the default LLVM code model so far, which is "small" in LLVM-speak and "normal" in LoongArch-speak. As described in the "Code Model" section of LoongArch ELF psABI spec v20231219 [1], one can only make function calls as far as ±128MiB with the "normal" code model; this is insufficient for very large software containing Rust components that needs to be linked into the big text section, such as Chromium. Because: * we do not want to ask users to recompile std if they are to build such software, * objects compiled with larger code models can be linked with those with smaller code models without problems, and * the "medium" code model is comparable to the "small"/"normal" one performance-wise (same data access pattern; each function call becomes 2-insn long and indirect, but this may be relaxed back into the direct 1-insn form in a future LLVM version), but is able to perform function calls within ±128GiB, it is better to just switch the targets to the "medium" code model, which is also "medium" in LLVM-speak. Relands [2]: rust-lang#120661 [1]: https://github.com/loongson/la-abi-specs/blob/v2.30/laelf.adoc#code-models [2]: rust-lang#121289 (comment)
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The Rust LoongArch targets have been using the default LLVM code model so far, which is "small" in LLVM-speak and "normal" in LoongArch-speak. As described in the "Code Model" section of LoongArch ELF psABI spec v20231219 1, one can only make function calls as far as ±128MiB with the "normal" code model; this is insufficient for very large software containing Rust components that needs to be linked into the big text section, such as Chromium.
Because:
it is better to just switch the targets to the "medium" code model, which is also "medium" in LLVM-speak.
Relands 2: #120661