Add mechanism for skipping MIR passes

Author: ecstatic-morse

compiler/rustc_interface/src/tests.rs

@@ -558,6 +558,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(link_only, true);
     tracked!(merge_functions, Some(MergeFunctions::Disabled));
     tracked!(mir_emit_retag, true);
+    tracked!(mir_opt_skip_pass, vec!["ConstProp".to_owned()]);
     tracked!(mir_opt_level, 3);
     tracked!(mutable_noalias, true);
     tracked!(new_llvm_pass_manager, true);

compiler/rustc_mir/src/transform/pass.rs

@@ -72,17 +72,25 @@ impl PassManager<'mir, 'tcx> {
         ret
     }
 
-    fn is_pass_enabled(&self, level: OptLevel) -> bool {
+    fn is_pass_enabled<P>(&self, pass: &P) -> bool
+    where
+        P: MirPass<'tcx>,
+    {
         let opts = &self.tcx.sess.opts.debugging_opts;
-        let level_required = match level {
+        let level_required = match P::LEVEL {
             OptLevel::Cleanup => return !self.skip_cleanup,
             OptLevel::Unsound if !opts.unsound_mir_opts => return false,
 
             OptLevel::Unsound => UNSOUND_MIR_OPT_LEVEL,
             OptLevel::N(n) => n,
         };
 
-        opts.mir_opt_level >= level_required as usize
+        // Optimization passes that are not always run can be disabled
+        if level_required != 0 && is_skipped(&pass.name(), &opts.mir_opt_skip_pass) {
+            return false;
+        }
+
+        opts.mir_opt_level >= level_required.into()
     }
 
     pub fn validate(&self, when: &str) {
@@ -145,3 +153,10 @@ macro_rules! run_passes {
         $( manager.run_pass(&$pass); )*
     }}
 }
+
+fn is_skipped(pass_name: &str, skipped_passes: &[String]) -> bool {
+    skipped_passes
+        .into_iter()
+        .filter(|skipped| !skipped.is_empty())
+        .any(|skipped| pass_name.starts_with(skipped))
+}

compiler/rustc_session/src/options.rs

@@ -959,6 +959,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     mir_emit_retag: bool = (false, parse_bool, [TRACKED],
         "emit Retagging MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \
         (default: no)"),
+    mir_opt_skip_pass: Vec<String> = (Vec::new(), parse_string_push, [TRACKED],
+        "MIR optimization passes that will not run (default: [])"),
     mir_opt_level: usize = (1, parse_uint, [TRACKED],
         "MIR optimization level (0-3; default: 1)"),
     mutable_noalias: bool = (false, parse_bool, [TRACKED],