Add -Zmutable-noalias flag

rust-lang · Oct 3, 2017 · 3647129 · 3647129
1 parent 4502e2a
commit 3647129
Show file tree

Hide file tree

Showing 2 changed files with 12 additions and 1 deletion.
diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
@@ -1060,6 +1060,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "print the result of the translation item collection pass"),
     mir_opt_level: usize = (1, parse_uint, [TRACKED],
           "set the MIR optimization level (0-3, default: 1)"),
+    mutable_noalias: bool = (false, parse_bool, [UNTRACKED],
+          "emit noalias metadata for mutable references"),
     dump_mir: Option<String> = (None, parse_opt_string, [UNTRACKED],
           "dump MIR state at various points in translation"),
     dump_mir_dir: Option<String> = (None, parse_opt_string, [UNTRACKED],

diff --git a/src/librustc_trans/abi.rs b/src/librustc_trans/abi.rs
@@ -760,7 +760,16 @@ impl<'a, 'tcx> FnType<'tcx> {
                 // on memory dependencies rather than pointer equality
                 let is_freeze = ccx.shared().type_is_freeze(mt.ty);
 
-                if mt.mutbl != hir::MutMutable && is_freeze {
+                let no_alias_is_safe =
+                    if ccx.shared().tcx().sess.opts.debugging_opts.mutable_noalias {
+                        // Mutable refrences or immutable shared references
+                        mt.mutbl == hir::MutMutable || is_freeze
+                    } else {
+                        // Only immutable shared references
+                        mt.mutbl != hir::MutMutable && is_freeze
+                    };
+
+                if no_alias_is_safe {
                     arg.attrs.set(ArgAttribute::NoAlias);
                 }