Use optional values for inlining thresholds

Turn inlining threshold into optional values to make it possible to
configure different defaults depending on the current mir-opt-level.

Author: tmiasko

compiler/rustc_interface/src/tests.rs

@@ -557,8 +557,8 @@ fn test_debugging_options_tracking_hash() {
     tracked!(human_readable_cgu_names, true);
     tracked!(inline_in_all_cgus, Some(true));
     tracked!(inline_mir, Some(true));
-    tracked!(inline_mir_threshold, 123);
-    tracked!(inline_mir_hint_threshold, 123);
+    tracked!(inline_mir_threshold, Some(123));
+    tracked!(inline_mir_hint_threshold, Some(123));
     tracked!(insert_sideeffect, true);
     tracked!(instrument_coverage, true);
     tracked!(instrument_mcount, true);

compiler/rustc_mir/src/transform/inline.rs

@@ -316,9 +316,9 @@ impl Inliner<'tcx> {
         }
 
         let mut threshold = if hinted {
-            self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold
+            self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold.unwrap_or(100)
         } else {
-            self.tcx.sess.opts.debugging_opts.inline_mir_threshold
+            self.tcx.sess.opts.debugging_opts.inline_mir_threshold.unwrap_or(50)
         };
 
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {

compiler/rustc_session/src/options.rs

@@ -958,9 +958,9 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "verify incr. comp. hashes of green query instances (default: no)"),
     inline_mir: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "enable MIR inlining (default: no)"),
-    inline_mir_threshold: usize = (50, parse_uint, [TRACKED],
+    inline_mir_threshold: Option<usize> = (None, parse_opt_uint, [TRACKED],
         "a default MIR inlining threshold (default: 50)"),
-    inline_mir_hint_threshold: usize = (100, parse_uint, [TRACKED],
+    inline_mir_hint_threshold: Option<usize> = (None, parse_opt_uint, [TRACKED],
         "inlining threshold for functions with inline hint (default: 100)"),
     inline_in_all_cgus: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "control whether `#[inline]` functions are in all CGUs"),