Add regression tests for promotion mir expansion

Author: oli-obk

src/test/mir-opt/const_prop/ref_deref.rs

@@ -3,6 +3,24 @@ fn main() {
 }
 
 // END RUST SOURCE
+// START rustc.main.PromoteTemps.before.mir
+// bb0: {
+//     ...
+//     _3 = const 4i32;
+//     _2 = &_3;
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.PromoteTemps.before.mir
+// START rustc.main.PromoteTemps.after.mir
+// bb0: {
+//     ...
+//     _4 = const main::promoted[0];
+//     _2 = &(*_4);
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.PromoteTemps.after.mir
 // START rustc.main.ConstProp.before.mir
 // bb0: {
 //     ...

src/test/mir-opt/const_prop/ref_deref_project.rs

@@ -0,0 +1,41 @@
+fn main() {
+    *(&(4, 5).1);
+}
+
+// END RUST SOURCE
+// START rustc.main.PromoteTemps.before.mir
+// bb0: {
+//     ...
+//     _3 = (const 4i32, const 5i32);
+//     _2 = &(_3.1: i32);
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.PromoteTemps.before.mir
+// START rustc.main.PromoteTemps.after.mir
+// bb0: {
+//     ...
+//     _4 = const main::promoted[0];
+//     _2 = &((*_4).1: i32);
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.PromoteTemps.after.mir
+// START rustc.main.ConstProp.before.mir
+// bb0: {
+//     ...
+//     _4 = const main::promoted[0];
+//     _2 = &((*_4).1: i32);
+//     _1 = (*_2);
+//     ...
+//}
+// END rustc.main.ConstProp.before.mir
+// START rustc.main.ConstProp.after.mir
+// bb0: {
+//     ...
+//     _4 = const main::promoted[0];
+//     _2 = &((*_4).1: i32);
+//     _1 = const 5i32;
+//     ...
+// }
+// END rustc.main.ConstProp.after.mir