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authorMatthias Krüger <matthias.krueger@famsik.de>2024-02-05 11:07:28 +0100
committerGitHub <noreply@github.com>2024-02-05 11:07:28 +0100
commitdc0b1f961a42e5200831cea9f34973320069620f (patch)
treeff35353ce11549191a14d4e7b1cda713edc1a0a3 /compiler/rustc_pattern_analysis/src/lib.rs
parent13ea09b22f2b741a6326fb993bfe6d813f128496 (diff)
parent35dad14dfb63d77cf4a2077f1e8e9cff5a02a92b (diff)
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Rollup merge of #120661 - xen0n:loong-medium-cmodel, r=heiher,Nilstrieb
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][1] in the "Code Model" section of LoongArch ELF psABI spec v20231219, 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
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