[C PATCH] Drop qualifiers of assignment expressions [PR 97981]

[Uecker, Martin]

Here is a patch to drop qualifiers in assignment expressions.

-- Martin



C: Drop qualifiers of assignment expressions. [PR98047]

ISO C17 6.5.15.1 specifies that the result is the
type the LHS would have after lvalue conversion.

    
2020-12-12  Martin Uecker  <muecker@gwdg.de>
    
gcc/c/
     PR c/98047
     * c-typeck.c (build_modify_expr): Drop qualifiers.      

gcc/testsuite/
     PR c/98047
     * gcc.dg/qual-assign-7.c.c: New test.


diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 138af073925..d8b2ca12766 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6276,16 +6276,9 @@ build_modify_expr (location_t location, tree lhs, tree lhs_origtype,
 		    "enum conversion in assignment is invalid in C++");
     }
 
-  /* If the lhs is atomic, remove that qualifier.  */
-  if (is_atomic_op)
-    {
-      lhstype = build_qualified_type (lhstype, 
-				      (TYPE_QUALS (lhstype)
-				       & ~TYPE_QUAL_ATOMIC));
-      olhstype = build_qualified_type (olhstype, 
-				       (TYPE_QUALS (lhstype)
-					& ~TYPE_QUAL_ATOMIC));
-    }
+  /* Remove qualifiers.  */
+  lhstype = build_qualified_type (lhstype, TYPE_UNQUALIFIED);
+  olhstype = build_qualified_type (olhstype, TYPE_UNQUALIFIED);
 
   /* Convert new value to destination type.  Fold it first, then
      restore any excess precision information, for the sake of
diff --git a/gcc/testsuite/gcc.dg/qual-assign-7.c b/gcc/testsuite/gcc.dg/qual-assign-7.c
new file mode 100644
index 00000000000..3e064e82f5f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/qual-assign-7.c
@@ -0,0 +1,18 @@
+/* test that assignment drops qualifiers, Bug 98047 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+
+volatile int jv;
+extern int j;
+extern typeof(jv = 1) j;
+
+_Atomic int ja;
+extern typeof(ja = 1) j;
+
+int * __restrict pa;
+extern int *p;
+extern typeof(pa = 0) p;
+
+
+