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mark &T params without UnsafeCell<U> as readonly #16525

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Merged
merged 1 commit into from
Aug 16, 2014
Merged

mark &T params without UnsafeCell<U> as readonly #16525

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12 changes: 9 additions & 3 deletions src/librustc/middle/trans/base.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2280,7 +2280,7 @@ pub fn get_fn_llvm_attributes(ccx: &CrateContext, fn_ty: ty::t)
match ty::get(ret_ty).sty {
// `~` pointer return values never alias because ownership
// is transferred
ty::ty_uniq(it) if match ty::get(it).sty {
ty::ty_uniq(it) if match ty::get(it).sty {
ty::ty_str | ty::ty_vec(..) | ty::ty_trait(..) => true, _ => false
} => {}
ty::ty_uniq(_) => {
Expand Down Expand Up @@ -2356,15 +2356,21 @@ pub fn get_fn_llvm_attributes(ccx: &CrateContext, fn_ty: ty::t)
}

// `&mut` pointer parameters never alias other parameters, or mutable global data
// `&` pointer parameters never alias either (for LLVM's purposes) as long as the
// interior is safe
//
// `&T` where `T` contains no `UnsafeCell<U>` is immutable, and can be marked as both
// `readonly` and `noalias`, as LLVM's definition of `noalias` is based solely on
// memory dependencies rather than pointer equality
ty::ty_rptr(b, mt) if mt.mutbl == ast::MutMutable ||
!ty::type_contents(ccx.tcx(), mt.ty).interior_unsafe() => {

let llsz = llsize_of_real(ccx, type_of::type_of(ccx, mt.ty));
attrs.arg(idx, llvm::NoAliasAttribute)
.arg(idx, llvm::DereferenceableAttribute(llsz));

if mt.mutbl == ast::MutImmutable {
attrs.arg(idx, llvm::ReadOnlyAttribute);
}

match b {
ReLateBound(_, BrAnon(_)) => {
attrs.arg(idx, llvm::NoCaptureAttribute);
Expand Down