MIR: opt-in normalization of BasicBlock and Local numbering

compiler/rustc_mir_transform/src/lib.rs

@@ -3,6 +3,7 @@
 #![deny(rustc::diagnostic_outside_of_impl)]
 #![feature(box_patterns)]
 #![feature(drain_filter)]
+#![feature(is_sorted)]
 #![feature(let_chains)]
 #![feature(map_try_insert)]
 #![feature(min_specialization)]
@@ -84,6 +85,7 @@ mod match_branches;
 mod multiple_return_terminators;
 mod normalize_array_len;
 mod nrvo;
+mod prettify;
 mod ref_prop;
 mod remove_noop_landing_pads;
 mod remove_storage_markers;
@@ -581,6 +583,9 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &large_enums::EnumSizeOpt { discrepancy: 128 },
             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
             &add_call_guards::CriticalCallEdges,
+            // Cleanup for human readability, off by default.
+            &prettify::ReorderBasicBlocks,
+            &prettify::ReorderLocals,
             // Dump the end result for testing and debugging purposes.
             &dump_mir::Marker("PreCodegen"),
         ],