Add diff test for MatchBranchSimplification

Author: clubby789

tests/mir-opt/matches_reduce_branches.my_is_some.MatchBranchSimplification.diff

@@ -0,0 +1,36 @@
+- // MIR for `my_is_some` before MatchBranchSimplification
++ // MIR for `my_is_some` after MatchBranchSimplification
+  
+  fn my_is_some(_1: Option<T>) -> bool {
+      debug bar => _1;
+      let mut _0: bool;
+      let mut _2: isize;
+  
+      bb0: {
+          _2 = discriminant(_1);
+          switchInt(move _2) -> [0: bb2, 1: bb3, otherwise: bb1];
+      }
+  
+      bb1: {
+          unreachable;
+      }
+  
+      bb2: {
+          _0 = const false;
+          goto -> bb4;
+      }
+  
+      bb3: {
+          _0 = const true;
+          goto -> bb4;
+      }
+  
+      bb4: {
+          drop(_1) -> [return: bb5, unwind unreachable];
+      }
+  
+      bb5: {
+          return;
+      }
+  }
+  

tests/mir-opt/matches_reduce_branches.rs

@@ -19,6 +19,18 @@ fn foo(bar: Option<()>) {
     }
 }
 
+// EMIT_MIR matches_reduce_branches.my_is_some.MatchBranchSimplification.diff
+// Test for #131219.
+fn my_is_some<T>(bar: Option<T>) -> bool {
+    // CHECK-LABEL: fn my_is_some(
+    // CHECK: switchInt
+    // CHECK: return
+    match bar {
+        Some(_) => true,
+        None => false,
+    }
+}
+
 // EMIT_MIR matches_reduce_branches.bar.MatchBranchSimplification.diff
 fn bar(i: i32) -> (bool, bool, bool, bool) {
     // CHECK-LABEL: fn bar(
@@ -651,4 +663,7 @@ fn main() {
     let _: u8 = match_trunc_u16_u8_failed(EnumAu16::u0_0x0000);
 
     let _ = match_i128_u128(EnumAi128::A);
+
+    let _ = my_is_some::<()>(None);
+    let _ = my_is_some(Some(()));
 }