[aarch64] PR102376 - Emit better diagnostic for arch extensions in target attr

[Prathamesh Kulkarni]

Hi,
The attached patch emits a more verbose diagnostic for target attribute that
is an architecture extension needing a leading '+'.

For the following test,
void calculate(void) __attribute__ ((__target__ ("sve")));

With patch, the compiler now emits:
102376.c:1:1: error: arch extension ‘sve’ should be prepended with ‘+’
    1 | void calculate(void) __attribute__ ((__target__ ("sve")));
      | ^~~~

instead of:
102376.c:1:1: error: pragma or attribute ‘target("sve")’ is not valid
    1 | void calculate(void) __attribute__ ((__target__ ("sve")));
      | ^~~~

(This isn't specific to sve though).
OK to commit after bootstrap+test ?

Thanks,
Prathamesh
-------------- next part --------------
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index a9a1800af53..975f7faf968 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -17821,7 +17821,16 @@ aarch64_process_target_attr (tree args)
       num_attrs++;
       if (!aarch64_process_one_target_attr (token))
 	{
-	  error ("pragma or attribute %<target(\"%s\")%> is not valid", token);
+	  /* Check if token is possibly an arch extension without
+	     leading '+'.  */
+	  char *str = (char *) xmalloc (strlen (token) + 2);
+	  str[0] = '+';
+	  strcpy(str + 1, token);
+	  if (aarch64_handle_attr_isa_flags (str))
+	    error("arch extension %<%s%> should be prepended with %<+%>", token);
+	  else
+	    error ("pragma or attribute %<target(\"%s\")%> is not valid", token);
+	  free (str);
 	  return false;
 	}