Add diff test for MatchBranchSimplification

Author: clubby789

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

@@ -0,0 +1,33 @@
+- // 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;
++     let mut _3: isize;
+  
+      bb0: {
+          _2 = discriminant((*_1));
+-         switchInt(move _2) -> [1: bb2, otherwise: bb1];
+-     }
+- 
+-     bb1: {
+-         _0 = const false;
+-         goto -> bb3;
+-     }
+- 
+-     bb2: {
+-         _0 = const true;
+-         goto -> bb3;
+-     }
+- 
+-     bb3: {
++         StorageLive(_3);
++         _3 = move _2;
++         _0 = Eq(copy _3, const 1_isize);
++         StorageDead(_3);
+          return;
+      }
+  }
+  

tests/mir-opt/matches_reduce_branches.rs

@@ -19,6 +19,11 @@ fn foo(bar: Option<()>) {
     }
 }
 
+// EMIT_MIR matches_reduce_branches.my_is_some.MatchBranchSimplification.diff
+fn my_is_some<T>(bar: &Option<T>) -> bool {
+    matches!(bar, Some(_))
+}
+
 // EMIT_MIR matches_reduce_branches.bar.MatchBranchSimplification.diff
 fn bar(i: i32) -> (bool, bool, bool, bool) {
     // CHECK-LABEL: fn bar(
@@ -651,4 +656,7 @@ 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(()));
 }