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target: default to the medium code model on LoongArch targets

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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
This commit is contained in:
WANG Xuerui 2024-02-05 13:18:32 +08:00
parent 991a9dc3f7
commit 35dad14dfb
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GPG key ID: 99797B0EB13A6337
3 changed files with 4 additions and 3 deletions
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3
compiler/rustc_target/src/spec/targets/loongarch64_unknown_linux_gnu.rs
View file

@ -1,4 +1,4 @@
use crate::spec::{base, Target, TargetOptions};
use crate::spec::{base, CodeModel, Target, TargetOptions};
pub fn target() -> Target {
Target {
@ -7,6 +7,7 @@ pub fn target() -> Target {
data_layout: "e-m:e-p:64:64-i64:64-i128:128-n64-S128".into(),
arch: "loongarch64".into(),
options: TargetOptions {
code_model: Some(CodeModel::Medium),
cpu: "generic".into(),
features: "+f,+d".into(),
llvm_abiname: "lp64d".into(),

2
compiler/rustc_target/src/spec/targets/loongarch64_unknown_none.rs
View file

@ -16,7 +16,7 @@ pub fn target() -> Target {
max_atomic_width: Some(64),
relocation_model: RelocModel::Static,
panic_strategy: PanicStrategy::Abort,
code_model: Some(CodeModel::Small),
code_model: Some(CodeModel::Medium),
..Default::default()
},
}

2
compiler/rustc_target/src/spec/targets/loongarch64_unknown_none_softfloat.rs
View file

@ -17,7 +17,7 @@ pub fn target() -> Target {
max_atomic_width: Some(64),
relocation_model: RelocModel::Static,
panic_strategy: PanicStrategy::Abort,
code_model: Some(CodeModel::Small),
code_model: Some(CodeModel::Medium),
..Default::default()
},
}