New MIR optimization pass to reduce branches on match of tuples of enums

compiler/rustc_mir/src/transform/mod.rs

@@ -26,6 +26,7 @@ pub mod copy_prop;
 pub mod deaggregator;
 pub mod dest_prop;
 pub mod dump_mir;
+pub mod early_otherwise_branch;
 pub mod elaborate_drops;
 pub mod generator;
 pub mod inline;
@@ -465,6 +466,7 @@ fn run_optimization_passes<'tcx>(
         &instcombine::InstCombine,
         &const_prop::ConstProp,
         &simplify_branches::SimplifyBranches::new("after-const-prop"),
+        &early_otherwise_branch::EarlyOtherwiseBranch,
         &simplify_comparison_integral::SimplifyComparisonIntegral,
         &simplify_try::SimplifyArmIdentity,
         &simplify_try::SimplifyBranchSame,