Add regression test showcasing miscompilation

src/test/mir-opt/76803_regression.encode.SimplifyBranchSame.diff

@@ -0,0 +1,30 @@
+- // MIR for `encode` before SimplifyBranchSame
++ // MIR for `encode` after SimplifyBranchSame
+
+ fn encode(_1: Type) -> Type {
+ debug v => _1; // in scope 0 at $DIR/76803_regression.rs:10:15: 10:16
+ let mut _0: Type; // return place in scope 0 at $DIR/76803_regression.rs:10:27: 10:31
+ let mut _2: isize; // in scope 0 at $DIR/76803_regression.rs:12:9: 12:16
+
+ bb0: {
+ _2 = discriminant(_1); // scope 0 at $DIR/76803_regression.rs:12:9: 12:16
+- switchInt(move _2) -> [0_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/76803_regression.rs:12:9: 12:16
++ goto -> bb1; // scope 0 at $DIR/76803_regression.rs:12:9: 12:16
+ }
+
+ bb1: {
+ _0 = move _1; // scope 0 at $DIR/76803_regression.rs:13:14: 13:15
+- goto -> bb3; // scope 0 at $DIR/76803_regression.rs:11:5: 14:6
++ goto -> bb2; // scope 0 at $DIR/76803_regression.rs:11:5: 14:6
+ }
+
+ bb2: {
+- discriminant(_0) = 1; // scope 0 at $DIR/76803_regression.rs:12:20: 12:27
+- goto -> bb3; // scope 0 at $DIR/76803_regression.rs:11:5: 14:6
+- }
+- 
+- bb3: {
+ return; // scope 0 at $DIR/76803_regression.rs:15:2: 15:2
+ }
+ }
+

src/test/mir-opt/76803_regression.rs

@@ -0,0 +1,19 @@
+// compile-flags: -Z mir-opt-level=1
+// EMIT_MIR 76803_regression.encode.SimplifyBranchSame.diff
+
+#[derive(Debug, Eq, PartialEq)]
+pub enum Type {
+ A,
+ B,
+}
+
+pub fn encode(v: Type) -> Type {
+ match v {
+ Type::A => Type::B,
+ _ => v,
+ }
+}
+
+fn main() {
+ assert_eq!(Type::B, encode(Type::A));
+}