target: default to the medium code model on LoongArch targets by heiher · Pull Request #130266 · rust-lang/rust (original) (raw)
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request
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