Gate move elimination behind -Z mir-move-elimination

This flag also has the effect of disabling DestinationPropagation, which
is already covered by move elimination.

Author: Amanieu

compiler/rustc_interface/src/tests.rs

@@ -848,6 +848,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(min_function_alignment, Some(Align::EIGHT));
     tracked!(min_recursion_limit, Some(256));
     tracked!(mir_enable_passes, vec![("DestProp".to_string(), false)]);
+    tracked!(mir_move_elimination, true);
     tracked!(mir_opt_level, Some(4));
     tracked!(mir_preserve_ub, true);
     tracked!(move_size_limit, Some(4096));

compiler/rustc_mir_transform/src/dest_prop.rs

@@ -153,7 +153,7 @@ pub(super) struct DestinationPropagation;
 
 impl<'tcx> crate::MirPass<'tcx> for DestinationPropagation {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 2
+        sess.mir_opt_level() >= 2 && !sess.opts.unstable_opts.mir_move_elimination
     }
 
     #[tracing::instrument(level = "trace", skip(self, tcx, body))]

compiler/rustc_mir_transform/src/move_elimination.rs

@@ -125,7 +125,7 @@ pub(super) struct MoveElimination;
 
 impl<'tcx> crate::MirPass<'tcx> for MoveElimination {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 2
+        sess.mir_opt_level() >= 2 && sess.opts.unstable_opts.mir_move_elimination
     }
 
     #[tracing::instrument(level = "trace", skip(self, tcx, body))]

compiler/rustc_mir_transform/src/tail_copy_to_move.rs

@@ -40,7 +40,7 @@ pub(super) struct TailCopyToMove;
 
 impl<'tcx> crate::MirPass<'tcx> for TailCopyToMove {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.mir_opt_level() >= 2
+        sess.mir_opt_level() >= 2 && sess.opts.unstable_opts.mir_move_elimination
     }
 
     #[tracing::instrument(level = "trace", skip(self, _tcx, body))]

compiler/rustc_session/src/options.rs

@@ -2495,6 +2495,8 @@ options! {
     mir_include_spans: MirIncludeSpans = (MirIncludeSpans::default(), parse_mir_include_spans, [UNTRACKED],
         "include extra comments in mir pretty printing, like line numbers and statement indices, \
          details about types, etc. (boolean for all passes, 'nll' to enable in NLL MIR only, default: 'nll')"),
+    mir_move_elimination: bool = (false, parse_bool, [TRACKED],
+        "enable the experimental MIR move elimination pass (default: no)"),
     mir_opt_bisect_limit: Option<usize> = (None, parse_opt_number, [TRACKED],
         "limit the number of MIR optimization pass executions (global across all bodies). \
         Pass executions after this limit are skipped and reported. (default: no limit)"),