Add codegen test for #129795

tests/codegen/issues/issue-129795.rs

@@ -0,0 +1,17 @@
+//@ compile-flags: -Copt-level=3
+//@ min-llvm-version: 20
+#![crate_type = "lib"]
+
+// Ensure that a modulo operation with an operand that is known to be
+// a power-of-two is properly optimized.
+
+// CHECK-LABEL: @modulo_with_power_of_two_divisor
+// CHECK: add i64 %divisor, -1
+// CHECK-NEXT: and i64
+// CHECK-NEXT: ret i64
+#[no_mangle]
+pub fn modulo_with_power_of_two_divisor(dividend: u64, divisor: u64) -> u64 {
+    assert!(divisor.is_power_of_two());
+    // should be optimized to (dividend & (divisor - 1))
+    dividend % divisor
+}