c-family: Fix ICE with -Wsuggest-attribute [PR98487]

Here we crash because check_function_format was using TREE_PURPOSE
directly rather than using get_attribute_name.

	PR c/98487

gcc/c-family/ChangeLog:

	* c-format.cc (check_function_format): Use get_attribute_name.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wsuggest-attribute-1.c: New test.

2 files changed, 37 insertions, 1 deletions

diff --git a/gcc/c-family/c-format.cc b/gcc/c-family/c-format.cc
index 01adea4..08643c5 100644
--- a/gcc/c-family/c-format.cc
+++ b/gcc/c-family/c-format.cc
@@ -1215,7 +1215,7 @@ check_function_format (const_tree fn, tree attrs, int nargs,
 	      for (c = TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl));
 		   c;
 		   c = TREE_CHAIN (c))
-		if (is_attribute_p ("format", TREE_PURPOSE (c))
+		if (is_attribute_p ("format", get_attribute_name (c))
 		    && (decode_format_type (IDENTIFIER_POINTER
 					    (TREE_VALUE (TREE_VALUE (c))))
 			== info.format_type))
diff --git a/gcc/testsuite/c-c++-common/Wsuggest-attribute-1.c b/gcc/testsuite/c-c++-common/Wsuggest-attribute-1.c
new file mode 100644
index 0000000..8b5b398
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wsuggest-attribute-1.c
@@ -0,0 +1,36 @@
+/* PR c/98487 */
+/* { dg-do compile { target { c || c++11 } } } */
+/* { dg-options "-Wsuggest-attribute=format" } */
+
+#include <stdarg.h>
+
+[[gnu::__format__(__printf__, 1, 2)]]
+void
+do_printf(const char * const a0, ...)
+{
+  va_list ap;
+  va_start(ap, a0);
+  __builtin_vprintf(a0, ap);
+  va_end(ap);
+}
+
+[[gnu::__format__(__scanf__, 1, 2)]]
+void
+do_scanf(const char * const a0, ...)
+{
+  va_list ap;
+  va_start(ap, a0);
+  __builtin_vscanf(a0, ap);
+  va_end(ap);
+}
+
+struct tm;
+
+[[gnu::__format__(__strftime__, 1, 0)]]
+void
+do_strftime(const char * const a0, struct tm * a1)
+{
+  char buff[256];
+  __builtin_strftime(buff, sizeof(buff), a0, a1);
+  __builtin_puts(buff);
+}