Convert -Z mutable-noalias to Optional<bool>

The default value will dependend on the LLVM version in the future,
so don't specify one to start with.

Author: nikic

compiler/rustc_codegen_llvm/src/abi.rs

@@ -62,7 +62,7 @@ fn should_use_mutable_noalias(cx: &CodegenCx<'_, '_>) -> bool {
     //
     // For now, do not enable mutable_noalias by default at all, while the
     // issue is being figured out.
-    cx.tcx.sess.opts.debugging_opts.mutable_noalias
+    cx.tcx.sess.opts.debugging_opts.mutable_noalias.unwrap_or(false)
 }
 
 impl ArgAttributesExt for ArgAttributes {

compiler/rustc_interface/src/tests.rs

@@ -566,7 +566,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(merge_functions, Some(MergeFunctions::Disabled));
     tracked!(mir_emit_retag, true);
     tracked!(mir_opt_level, Some(4));
-    tracked!(mutable_noalias, true);
+    tracked!(mutable_noalias, Some(true));
     tracked!(new_llvm_pass_manager, true);
     tracked!(no_codegen, true);
     tracked!(no_generate_arange_section, true);

compiler/rustc_session/src/options.rs

@@ -997,7 +997,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         (default: no)"),
     mir_opt_level: Option<usize> = (None, parse_opt_uint, [TRACKED],
         "MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
-    mutable_noalias: bool = (false, parse_bool, [TRACKED],
+    mutable_noalias: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: no)"),
     new_llvm_pass_manager: bool = (false, parse_bool, [TRACKED],
         "use new LLVM pass manager (default: no)"),