From 48edb32a3fc8ba6cc3db9a9d11f5201a919391f5 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Fri, 15 Aug 2014 12:34:28 -0400
Subject: [PATCH] mark &T params without UnsafeCell<U> as readonly
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`.
---
src/librustc/middle/trans/base.rs | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index 9aa4355632c..351ccd9bf4d 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -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);