[C] Improve diagnostics for vector types

[Richard Sandiford <richard dot sandiford at arm dot com>]

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.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Richard


2019-09-30  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.

Index: gcc/c-family/c-pretty-print.c
===================================================================
--- gcc/c-family/c-pretty-print.c	2019-09-30 13:54:18.387750214 +0100
+++ gcc/c-family/c-pretty-print.c	2019-09-30 14:01:05.904830151 +0100
@@ -470,6 +470,16 @@ pp_c_specifier_qualifier_list (c_pretty_
 			     ? "_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));
Index: gcc/testsuite/gcc.dg/diag-aka-3.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/diag-aka-3.c	2019-09-30 14:01:05.904830151 +0100
@@ -0,0 +1,9 @@
+typedef unsigned int myvec __attribute__((vector_size (16)));
+
+void f (float x)
+{
+  myvec y = x; /* { dg-error {incompatible types when initializing type 'myvec' {aka '__vector\([48]\) unsigned int'} using type 'float'} } */
+  myvec *ptr = &x; /* { dg-error {initialization of 'myvec \*' {aka '__vector\([48]\) unsigned int \*'} from incompatible pointer type 'float \*'} } */
+  const myvec *const_ptr = &x; /* { dg-error {initialization of 'const myvec \*' {aka 'const __vector\([48]\) unsigned int \*'} from incompatible pointer type 'float \*'} } */
+  volatile myvec *volatile_ptr = &x; /* { dg-error {initialization of 'volatile myvec \*' {aka 'volatile __vector\([48]\) unsigned int \*'} from incompatible pointer type 'float \*'} } */
+}
Index: gcc/testsuite/gcc.target/aarch64/diag_aka_1.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.target/aarch64/diag_aka_1.c	2019-09-30 14:01:05.908830119 +0100
@@ -0,0 +1,14 @@
+#include <arm_neon.h>
+
+typedef int16x4_t myvec;
+
+void f (float x)
+{
+  __Int8x8_t y1 = x; /* { dg-error {incompatible types when initializing type '__Int8x8_t' using type 'float'} } */
+  __Int8x8_t *ptr1 = &x; /* { dg-error {initialization of '__Int8x8_t \*' from incompatible pointer type 'float \*'} } */
+  int8x8_t y2 = x; /* { dg-error {incompatible types when initializing type 'int8x8_t' using type 'float'} } */
+  int8x8_t *ptr2 = &x; /* { dg-error {initialization of 'int8x8_t \*' from incompatible pointer type 'float \*'} } */
+  /* ??? For these it would be better to print an aka for 'int16x4_t'.  */
+  myvec y3 = x; /* { dg-error {incompatible types when initializing type 'myvec' using type 'float'} } */
+  myvec *ptr3 = &x; /* { dg-error {initialization of 'myvec \*' from incompatible pointer type 'float \*'} } */
+}
Index: gcc/testsuite/g++.dg/diagnostic/aka4.C
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/g++.dg/diagnostic/aka4.C	2019-09-30 14:01:05.904830151 +0100
@@ -0,0 +1,9 @@
+typedef unsigned int myvec __attribute__((vector_size (16)));
+
+void f (float x)
+{
+  myvec y = x; // { dg-error {cannot convert 'float' to 'myvec' {aka '__vector\([48]\) unsigned int'} in initialization} }
+  myvec *ptr = &x; // { dg-error {cannot convert 'float\*' to 'myvec\*' {aka '__vector\([48]\) unsigned int\*'} in initialization} }
+  const myvec *const_ptr = &x; // { dg-error {cannot convert 'float\*' to 'const myvec\*' {aka 'const __vector\([48]\) unsigned int\*'} in initialization} }
+  volatile myvec *volatile_ptr = &x; // { dg-error {cannot convert 'float\*' to 'volatile myvec\*' {aka 'volatile __vector\([48]\) unsigned int\*'} in initialization} }
+}