bjoernager/rust
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Rollup merge of #117744 - quininer:add-z-sync-uw, r=bjorn3

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Add -Zuse-sync-unwind

Currently Rust uses async unwind by default, but async unwind will bring non-negligible size overhead. it would be nice to allow users to choose this.

In addition, async unwind currently prevents LLVM from generate compact unwind for MachO, if one wishes to generate compact unwind for MachO, then also needs this flag.
This commit is contained in:
Matthias Krüger 2024-01-09 05:33:20 +01:00 • committed by GitHub
commit 9e4843e42e
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3 changed files with 8 additions and 4 deletions
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3
compiler/rustc_codegen_llvm/src/allocator.rs
View file

@ -134,7 +134,8 @@ fn create_wrapper_function(
llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
}
if tcx.sess.must_emit_unwind_tables() {
let uwtable = attributes::uwtable_attr(llcx);
let uwtable =
attributes::uwtable_attr(llcx, tcx.sess.opts.unstable_opts.use_sync_unwind);
attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[uwtable]);
}

7
compiler/rustc_codegen_llvm/src/attributes.rs
View file

@ -95,11 +95,12 @@ pub fn sanitize_attrs<'ll>(
/// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
#[inline]
pub fn uwtable_attr(llcx: &llvm::Context) -> &Attribute {
pub fn uwtable_attr(llcx: &llvm::Context, use_sync_unwind: Option<bool>) -> &Attribute {
// NOTE: We should determine if we even need async unwind tables, as they
// take have more overhead and if we can use sync unwind tables we
// probably should.
llvm::CreateUWTableAttr(llcx, true)
let async_unwind = !use_sync_unwind.unwrap_or(false);
llvm::CreateUWTableAttr(llcx, async_unwind)
}
pub fn frame_pointer_type_attr<'ll>(cx: &CodegenCx<'ll, '_>) -> Option<&'ll Attribute> {
@ -333,7 +334,7 @@ pub fn from_fn_attrs<'ll, 'tcx>(
// You can also find more info on why Windows always requires uwtables here:
// https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
if cx.sess().must_emit_unwind_tables() {
to_add.push(uwtable_attr(cx.llcx));
to_add.push(uwtable_attr(cx.llcx, cx.sess().opts.unstable_opts.use_sync_unwind));
}
if cx.sess().opts.unstable_opts.profile_sample_use.is_some() {