add test for not optimized pow with constant power

Closes #34947

Author: Dushistov

src/test/codegen/issue-34947-pow-i32.rs

@@ -0,0 +1,23 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -O
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: @issue_34947
+#[no_mangle]
+pub fn issue_34947(x: i32) -> i32 {
+    // CHECK: mul
+    // CHECK-NEXT: mul
+    // CHECK-NEXT: mul
+    // CHECK-NEXT: ret
+    x.pow(5)
+}