Run combine_duplicate_switch_targets after the simplification that produces them

Author: saethlin

compiler/rustc_mir_transform/src/instcombine.rs

@@ -1,11 +1,9 @@
 //! Performs various peephole optimizations.
 
+use crate::simplify::combine_duplicate_switch_targets;
 use crate::MirPass;
 use rustc_hir::Mutability;
-use rustc_middle::mir::{
-    BinOp, Body, CastKind, Constant, ConstantKind, LocalDecls, Operand, Place, ProjectionElem,
-    Rvalue, SourceInfo, Statement, StatementKind, SwitchTargets, Terminator, TerminatorKind, UnOp,
-};
+use rustc_middle::mir::*;
 use rustc_middle::ty::layout::ValidityRequirement;
 use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, ParamEnv, SubstsRef, Ty, TyCtxt};
@@ -46,7 +44,7 @@ impl<'tcx> MirPass<'tcx> for InstCombine {
                 &mut block.terminator.as_mut().unwrap(),
                 &mut block.statements,
             );
-            ctx.combine_duplicate_switch_targets(&mut block.terminator.as_mut().unwrap());
+            combine_duplicate_switch_targets(block.terminator.as_mut().unwrap());
         }
     }
 }
@@ -264,19 +262,6 @@ impl<'tcx> InstCombineContext<'tcx, '_> {
         terminator.kind = TerminatorKind::Goto { target: destination_block };
     }
 
-    fn combine_duplicate_switch_targets(&self, terminator: &mut Terminator<'tcx>) {
-        let TerminatorKind::SwitchInt { targets, .. } = &mut terminator.kind
-        else { return };
-
-        let otherwise = targets.otherwise();
-        if targets.iter().any(|t| t.1 == otherwise) {
-            *targets = SwitchTargets::new(
-                targets.iter().filter(|t| t.1 != otherwise),
-                targets.otherwise(),
-            );
-        }
-    }
-
     fn combine_intrinsic_assert(
         &self,
         terminator: &mut Terminator<'tcx>,

compiler/rustc_mir_transform/src/simplify.rs

@@ -278,6 +278,18 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
     }
 }
 
+pub fn combine_duplicate_switch_targets(terminator: &mut Terminator<'_>) {
+    if let TerminatorKind::SwitchInt { targets, .. } = &mut terminator.kind {
+        let otherwise = targets.otherwise();
+        if targets.iter().any(|t| t.1 == otherwise) {
+            *targets = SwitchTargets::new(
+                targets.iter().filter(|t| t.1 != otherwise),
+                targets.otherwise(),
+            );
+        }
+    }
+}
+
 pub fn remove_duplicate_unreachable_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     struct OptApplier<'tcx> {
         tcx: TyCtxt<'tcx>,
@@ -298,6 +310,8 @@ pub fn remove_duplicate_unreachable_blocks<'tcx>(tcx: TyCtxt<'tcx>, body: &mut B
                 }
             }
 
+            combine_duplicate_switch_targets(terminator);
+
             self.super_terminator(terminator, location);
         }
     }

tests/mir-opt/inline/unwrap_unchecked.unwrap_unchecked.Inline.diff

@@ -34,7 +34,7 @@
 -                                          // + literal: Const { ty: unsafe fn(Option<T>) -> T {Option::<T>::unwrap_unchecked}, val: Value(<ZST>) }
 +         StorageLive(_3);                 // scope 0 at $DIR/unwrap_unchecked.rs:+1:9: +1:27
 +         _4 = discriminant(_2);           // scope 1 at $SRC_DIR/core/src/option.rs:LL:COL
-+         switchInt(move _4) -> [0: bb1, 1: bb2, otherwise: bb1]; // scope 1 at $SRC_DIR/core/src/option.rs:LL:COL
++         switchInt(move _4) -> [1: bb2, otherwise: bb1]; // scope 1 at $SRC_DIR/core/src/option.rs:LL:COL
       }
 
       bb1: {

tests/mir-opt/instcombine_duplicate_switch_targets_e2e.ub_if_b.PreCodegen.after.mir

@@ -13,7 +13,7 @@ fn ub_if_b(_1: Thing) -> Thing {
 
     bb0: {
         _2 = discriminant(_1);           // scope 0 at $DIR/instcombine_duplicate_switch_targets_e2e.rs:+1:11: +1:12
-        switchInt(move _2) -> [0: bb2, 1: bb1, otherwise: bb1]; // scope 0 at $DIR/instcombine_duplicate_switch_targets_e2e.rs:+1:5: +1:12
+        switchInt(move _2) -> [0: bb2, otherwise: bb1]; // scope 0 at $DIR/instcombine_duplicate_switch_targets_e2e.rs:+1:5: +1:12
     }
 
     bb1: {