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Add -Z small-data-threshold

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This flag allows specifying the threshold size above which LLVM should
not consider placing small objects in a .sdata or .sbss section.

Support is indicated in the target options via the
small-data-threshold-support target option, which can indicate either an
LLVM argument or an LLVM module flag.  To avoid duplicate specifications
in a large number of targets, the default value for support is
DefaultForArch, which is translated to a concrete value according to the
target's architecture.
This commit is contained in:
Paul Menage 2024-09-10 12:19:16 -07:00
parent 33855f80d4
commit 3810386bbe
10 changed files with 241 additions and 4 deletions
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20
compiler/rustc_codegen_llvm/src/context.rs
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@ -27,7 +27,7 @@ use rustc_span::source_map::Spanned;
use rustc_span::{Span, DUMMY_SP};
use rustc_target::abi::call::FnAbi;
use rustc_target::abi::{HasDataLayout, TargetDataLayout, VariantIdx};
use rustc_target::spec::{HasTargetSpec, RelocModel, Target, TlsModel};
use rustc_target::spec::{HasTargetSpec, RelocModel, SmallDataThresholdSupport, Target, TlsModel};
use smallvec::SmallVec;
use crate::back::write::to_llvm_code_model;
@ -387,6 +387,24 @@ pub(crate) unsafe fn create_module<'ll>(
}
}
match (sess.opts.unstable_opts.small_data_threshold, sess.target.small_data_threshold_support())
{
// Set up the small-data optimization limit for architectures that use
// an LLVM module flag to control this.
(Some(threshold), SmallDataThresholdSupport::LlvmModuleFlag(flag)) => {
let flag = SmallCStr::new(flag.as_ref());
unsafe {
llvm::LLVMRustAddModuleFlagU32(
llmod,
llvm::LLVMModFlagBehavior::Error,
flag.as_c_str().as_ptr(),
threshold as u32,
)
}
}
_ => (),
};
// Insert `llvm.ident` metadata.
//
// On the wasm targets it will get hooked up to the "producer" sections