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mark &T params without UnsafeCell<U> as readonly

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These are already marked as `noalias` due to the immutability guarantee
(see 4c2d4cd3dea344e81e4df24382ac3f23e2f86f40), but more information can
be bubbled up to the caller via `readonly`.
This commit is contained in:
Daniel Micay 2014-08-15 12:34:28 -04:00
parent cafa47506d
commit 48edb32a3f
1 changed files with 9 additions and 3 deletions
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12
src/librustc/middle/trans/base.rs
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@ -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(_) => {
@ -2356,8 +2356,10 @@ 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() => {
@ -2365,6 +2367,10 @@ pub fn get_fn_llvm_attributes(ccx: &CrateContext, fn_ty: ty::t)
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);