openmp: Mark OpenMP atomic write expression as read [PR119000]

The following testcase was emitting false positive warning that
the rhs of #pragma omp atomic write was stored but not read,
when the atomic actually does read it.  The following patch
fixes that by calling default_function_array_read_conversion
on it, so that it is marked as read as well as converted from
lvalue to rvalue.
Furthermore, the code had
if (code == NOP_EXPR) ... else ... if (code == NOP_EXPR) ...
with none of ... parts changing code, so I've merged the two ifs.

2025-02-25  Jakub Jelinek  <jakub@redhat.com>

	PR c/119000
	* c-parser.cc (c_parser_omp_atomic): For omp write call
	default_function_array_read_conversion on the rhs expression.
	Merge the two adjacent if (code == NOP_EXPR) blocks.

	* c-c++-common/gomp/pr119000.c: New test.

(cherry picked from commit cdffc76393488a73671b70481cf8a4b7c289029d)

diff --git a/gcc/c/c-parser.cc b/gcc/c/c-parser.cc
index 9264581da558a31cae9625b3982daf45b3a0fc92..ed292db4248cac6f523b0a1c5381af88744a9996 100644 (file)
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -18320,9 +18320,16 @@ c_parser_omp_atomic (location_t loc, c_parser *parser, bool openacc)
        goto saw_error;
       if (code == NOP_EXPR)
        {
-         lhs = c_parser_expression (parser).value;
-         lhs = c_fully_fold (lhs, false, NULL);
-         if (lhs == error_mark_node)
+         eloc = c_parser_peek_token (parser)->location;
+         expr = c_parser_expression (parser);
+         expr = default_function_array_read_conversion (eloc, expr);
+         /* atomic write is represented by OMP_ATOMIC with NOP_EXPR
+            opcode.  */
+         code = OMP_ATOMIC;
+         lhs = v;
+         v = NULL_TREE;
+         rhs = c_fully_fold (expr.value, false, NULL);
+         if (rhs == error_mark_node)
            goto saw_error;
        }
       else
@@ -18335,15 +18342,6 @@ c_parser_omp_atomic (location_t loc, c_parser *parser, bool openacc)
          if (non_lvalue_p)
            lhs = non_lvalue (lhs);
        }
-      if (code == NOP_EXPR)
-       {
-         /* atomic write is represented by OMP_ATOMIC with NOP_EXPR
-            opcode.  */
-         code = OMP_ATOMIC;
-         rhs = lhs;
-         lhs = v;
-         v = NULL_TREE;
-       }
       goto done;
     case OMP_ATOMIC_CAPTURE_NEW:
       if (c_parser_next_token_is (parser, CPP_OPEN_BRACE))

diff --git a/gcc/testsuite/c-c++-common/gomp/pr119000.c b/gcc/testsuite/c-c++-common/gomp/pr119000.c
new file mode 100644 (file)
index 0000000..e5b7ab0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/gomp/pr119000.c
@@ -0,0 +1,16 @@
+/* PR c/119000 */
+/* { dg-do compile } */
+/* { dg-options "-fopenmp -Wunused-but-set-variable" } */
+
+int
+foo (void)
+{
+  int a = 1, b, c = 1, v;      /* { dg-warning "variable 'b' set but not used" } */
+  #pragma omp atomic write
+  v = a;
+  #pragma omp atomic read
+  b = v;
+  #pragma omp atomic update
+  v += c;
+  return v;
+}