[C] Improve diagnostics for vector types

Given the following invalid arm_neon.h-based code:

  float x;
  int8x8_t y = x;

the error message we emit is pretty good:

  incompatible types when initializing type 'int8x8_t' using type 'float'

But convert the types to pointers:

  int8x8_t *ptr = &x;

and the message becomes:

  initialization of '__vector(8) signed char *' from incompatible pointer type 'float *'

Although it's reasonably obvious what '__vector(8) signed char *' means,
it isn't valid C or C++ syntax and is quite far from what the user wrote,
so using 'int8x8_t *' would be better.

This patch therefore prints the type name of vectors that have one.
It's still OK to print the __vector syntax as an "aka", although I have
a follow-on patch to tweak this slightly for types defined in system
header files.  The follow-on patch also addresses the ??? in
gcc.target/aarch64/diag_aka_1.c.

The C++ test already passed, but it seemed worth including for
consistency.

2019-10-01  Richard Sandiford  <richard.sandiford@arm.com>

gcc/c-family/
	* c-pretty-print.c (pp_c_specifier_qualifier_list): If a vector type
	has a type name, use it in preference to the __vector syntax.

gcc/testsuite/
	* gcc.dg/diag-aka-3.c: New test.
	* gcc.target/aarch64/diag_aka_1.c: New test.
	* g++.dg/diagnostic/aka4.C: New test.

From-SVN: r276394

1 files changed, 10 insertions, 0 deletions

diff --git a/gcc/c-family/c-pretty-print.c b/gcc/c-family/c-pretty-print.c
index e5cad67..1b06cc2 100644
--- a/gcc/c-family/c-pretty-print.c
+++ b/gcc/c-family/c-pretty-print.c
@@ -470,6 +470,16 @@ pp_c_specifier_qualifier_list (c_pretty_printer *pp, tree t)
 			     ? "_Complex" : "__complex__"));
       else if (code == VECTOR_TYPE)
 	{
+	  /* The syntax we print for vector types isn't real C or C++ syntax,
+	     so it's better to print the type name if we have one.  */
+	  tree name = TYPE_NAME (t);
+	  if (!(pp->flags & pp_c_flag_gnu_v3)
+	      && name
+	      && TREE_CODE (name) == TYPE_DECL)
+	    {
+	      pp->id_expression (name);
+	      break;
+	    }
 	  pp_c_ws_string (pp, "__vector");
 	  pp_c_left_paren (pp);
 	  pp_wide_integer (pp, TYPE_VECTOR_SUBPARTS (t));