Re: [PATCH 1/2] c++: correct __has_attribute(init_priority)

[Jason Merrill via Gcc-patches]

On 11/4/22 11:05, Patrick Palka wrote:

Currently __has_attribute(init_priority) always returns true, even on
targets that don't actually support init priorities, and when using
the attribute on such targets, we issue a hard error that init
priorities are unsupported.  This makes it impossible to conditionally
use the attribute by querying __has_attribute.

This patch fixes this by adding the attribute to the attribute table
only if the target supports init priorities, so that __has_attribute
returns false appropriately.  Thus on such targets we'll now treat it as
just another unrecognized attribute, so using it gives a -Wattribute
warning instead of an error.

OK.

gcc/cp/ChangeLog:

        * tree.cc (cxx_attribute_table): Add entry for init_priority
        only if SUPPORTS_INIT_PRIORITY.
        (handle_init_priority_attribute): Assert SUPPORTS_INIT_PRIORITY
        is true.

gcc/testsuite/ChangeLog:

        * g++.dg/special/initpri3.C: New test.
---
  gcc/cp/tree.cc                          | 20 +++++++-------------
  gcc/testsuite/g++.dg/special/initpri3.C |  9 +++++++++
  2 files changed, 16 insertions(+), 13 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/special/initpri3.C

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 45348c58bb6..c30bbeb0839 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -5010,8 +5010,10 @@ const struct attribute_spec cxx_attribute_table[] =
  {
    /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
         affects_type_identity, handler, exclude } */
+#if SUPPORTS_INIT_PRIORITY
    { "init_priority",  1, 1, true,  false, false, false,
      handle_init_priority_attribute, NULL },
+#endif
    { "abi_tag", 1, -1, false, false, false, true,
      handle_abi_tag_attribute, NULL },
    { NULL, 0, 0, false, false, false, false, NULL, NULL }
@@ -5039,7 +5041,7 @@ const struct attribute_spec std_attribute_table[] =

/* Handle an "init_priority" attribute; arguments as in

     struct attribute_spec.handler.  */
-static tree
+ATTRIBUTE_UNUSED static tree
  handle_init_priority_attribute (tree* node,
                                tree name,
                                tree args,
@@ -5103,18 +5105,10 @@ handle_init_priority_attribute (tree* node,
         pri);
      }

- if (SUPPORTS_INIT_PRIORITY)

-    {
-      SET_DECL_INIT_PRIORITY (decl, pri);
-      DECL_HAS_INIT_PRIORITY_P (decl) = 1;
-      return NULL_TREE;
-    }
-  else
-    {
-      error ("%qE attribute is not supported on this platform", name);
-      *no_add_attrs = true;
-      return NULL_TREE;
-    }
+  gcc_assert (SUPPORTS_INIT_PRIORITY);
+  SET_DECL_INIT_PRIORITY (decl, pri);
+  DECL_HAS_INIT_PRIORITY_P (decl) = 1;
+  return NULL_TREE;
  }

/* DECL is being redeclared; the old declaration had the abi tags in OLD,

diff --git a/gcc/testsuite/g++.dg/special/initpri3.C 
b/gcc/testsuite/g++.dg/special/initpri3.C
new file mode 100644
index 00000000000..a181abdd0b1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/special/initpri3.C
@@ -0,0 +1,9 @@
+// Verify __has_attribute(init_priority) is false whenever the platform
+// doesn't support it, and is treated as an unrecognized attribute.
+
+#if !__has_attribute(init_priority)
+#error init_priority /* { dg-error "" "" { target { ! init_priority } } } */
+#endif
+
+struct A { A(); } a __attribute__((init_priority(500)));
+// { dg-warning "attribute directive ignored" "" { target { ! init_priority } 
} .-1 }