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Add -Zuse-sync-unwind #117744

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Jan 9, 2024
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Add -Zuse-sync-unwind #117744

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3 changes: 2 additions & 1 deletion compiler/rustc_codegen_llvm/src/allocator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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]);
}

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7 changes: 4 additions & 3 deletions compiler/rustc_codegen_llvm/src/attributes.rs
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Expand Up @@ -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.
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@durin42 do you think unconditionally (or by default) using sync only unwind tables would work?

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> {
Expand Down Expand Up @@ -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() {
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2 changes: 2 additions & 0 deletions compiler/rustc_session/src/options.rs
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Expand Up @@ -1991,6 +1991,8 @@ written to standard error output)"),
"adds unstable command line options to rustc interface (default: no)"),
use_ctors_section: Option<bool> = (None, parse_opt_bool, [TRACKED],
"use legacy .ctors section for initializers rather than .init_array"),
use_sync_unwind: Option<bool> = (None, parse_opt_bool, [TRACKED],
"Generate sync unwind tables instead of async unwind tables (default: no)"),
validate_mir: bool = (false, parse_bool, [UNTRACKED],
"validate MIR after each transformation"),
#[rustc_lint_opt_deny_field_access("use `Session::verbose_internals` instead of this field")]
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