Add test for issue #91490

Author: nikic

src/test/codegen/merge-functions.rs

@@ -0,0 +1,14 @@
+// compile-flags: -O
+#![crate_type = "lib"]
+
+// CHECK: @func2 = {{.*}}alias{{.*}}@func1
+
+#[no_mangle]
+pub fn func1(c: char) -> bool {
+    c == 's' || c == 'm' || c == 'h' || c == 'd' || c == 'w'
+}
+
+#[no_mangle]
+pub fn func2(c: char) -> bool {
+    matches!(c, 's' | 'm' | 'h' | 'd' | 'w')
+}