Added a GVN storage test for borrowed value

Author: ohadravid

tests/mir-opt/gvn_storage_issue_141649.f_borrowed.GVN.diff

@@ -0,0 +1,25 @@
+- // MIR for `f_borrowed` before GVN
++ // MIR for `f_borrowed` after GVN
+  
+  fn f_borrowed(_1: u32) -> () {
+      let mut _0: ();
+      let mut _2: S;
+      let mut _3: S;
+      let mut _4: &S;
+      let mut _5: S;
+  
+      bb0: {
+-         StorageLive(_2);
++         nop;
+          _2 = S(copy _1, const 2_u32);
+-         _3 = S(copy _1, const 2_u32);
++         _3 = copy _2;
+          _4 = &_3;
+-         StorageDead(_2);
+-         _5 = copy (*_4);
++         nop;
++         _5 = copy _2;
+          return;
+      }
+  }
+  

tests/mir-opt/gvn_storage_issue_141649.rs

@@ -1,6 +1,7 @@
 //! Check that we do not remove storage statements when possible.
 //@ test-mir-pass: GVN
 // EMIT_MIR gvn_storage_issue_141649.f.GVN.diff
+// EMIT_MIR gvn_storage_issue_141649.f_borrowed.GVN.diff
 
 #![feature(custom_mir, core_intrinsics)]
 
@@ -30,3 +31,29 @@ pub fn f(_1: u32) {
         }
     }
 }
+
+#[custom_mir(dialect = "runtime")]
+pub fn f_borrowed(_1: u32) {
+    // CHECK-LABEL: fn f_borrowed(
+    mir! {
+        let _2: S;
+        let _3: S;
+        let _4: &S;
+        let _5: S;
+        {
+            // CHECK-NOT: StorageLive(_2);
+            // CHECK: _3 = copy _2;
+            // CHECK-NOT: StorageDead(_2);
+            // CHECK: _5 = copy _2;
+            StorageLive(_2);
+            _2 = S(_1, 2);
+            _3 = S(_1, 2);
+            _4 = &_3;
+            StorageDead(_2);
+            // Because `*_4` will be replaced with `_2`,
+            // we have to remove the storage statements of `_2`.
+            _5 = *_4;
+            Return()
+        }
+    }
+}