[PATCH] c: Avoid -Wenum-int-mismatch warning for redeclaration of builtin acc_on_device [PR107041]

[Jakub Jelinek via Gcc-patches]

Hi!

The new -Wenum-int-mismatch warning triggers with -Wsystem-headers in
<openacc.h>, for obvious reasons the builtin acc_on_device uses int
type argument rather than enum which isn't defined yet when the builtin
is created, while the OpenACC spec requires it to have acc_device_t
enum argument.  The header makes sure it has int underlying type by using
negative and __INT_MAX__ enumerators.

I've tried to make the builtin typegeneric or just varargs, but that
changes behavior e.g. when one calls it with some C++ class which has
cast operator to acc_device_t, so the following patch instead disables
the warning for this builtin.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
and 13.2?

2023-04-19  Jakub Jelinek  <ja...@redhat.com>

        PR c/107041
        * c-decl.cc (diagnose_mismatched_decls): Avoid -Wenum-int-mismatch
        warning on acc_on_device declaration.

        * gcc.dg/goacc/pr107041.c: New test.

--- gcc/c/c-decl.cc.jj  2023-03-10 10:10:17.918387120 +0100
+++ gcc/c/c-decl.cc     2023-04-18 10:29:33.340793562 +0200
@@ -2219,7 +2219,14 @@ diagnose_mismatched_decls (tree newdecl,
     }
   /* Warn about enum/integer type mismatches.  They are compatible types
      (C2X 6.7.2.2/5), but may pose portability problems.  */
-  else if (enum_and_int_p && TREE_CODE (newdecl) != TYPE_DECL)
+  else if (enum_and_int_p
+          && TREE_CODE (newdecl) != TYPE_DECL
+          /* Don't warn about about acc_on_device builtin redeclaration,
+             the builtin is declared with int rather than enum because
+             the enum isn't intrinsic.  */
+          && !(TREE_CODE (olddecl) == FUNCTION_DECL
+               && fndecl_built_in_p (olddecl, BUILT_IN_ACC_ON_DEVICE)
+               && !C_DECL_DECLARED_BUILTIN (olddecl)))
     warned = warning_at (DECL_SOURCE_LOCATION (newdecl),
                         OPT_Wenum_int_mismatch,
                         "conflicting types for %q+D due to enum/integer "
--- gcc/testsuite/gcc.dg/goacc/pr107041.c.jj    2023-04-18 10:18:07.039754258 
+0200
+++ gcc/testsuite/gcc.dg/goacc/pr107041.c       2023-04-18 10:17:21.252418797 
+0200
@@ -0,0 +1,23 @@
+/* PR c/107041 */
+/* { dg-do compile } */
+/* { dg-additional-options "-Wenum-int-mismatch" } */
+
+typedef enum acc_device_t {
+  acc_device_current = -1,
+  acc_device_none = 0,
+  acc_device_default = 1,
+  acc_device_host = 2,
+  acc_device_not_host = 4,
+  acc_device_nvidia = 5,
+  acc_device_radeon = 8,
+  _ACC_highest = __INT_MAX__
+} acc_device_t;
+
+int acc_on_device (acc_device_t);              /* { dg-bogus "conflicting 
types for 'acc_on_device' due to enum/integer mismatch; have 
'int\\\(acc_device_t\\\)'" } */
+int acc_on_device (acc_device_t);
+
+int
+foo (void)
+{
+  return acc_on_device (acc_device_host);
+}

        Jakub