c: improvements to address space diagnostics

This adds a clarifying "note" to address space mismatch diagnostics.
For example, it improves the diagnostic for
gcc.target/i386/addr-space-typeck-2.c from:

addr-space-typeck-2.c: In function 'test_bad_call':
addr-space-typeck-2.c:12:22: error: passing argument 2 of 'expects_seg_gs'
  from pointer to non-enclosed address space
   12 |   expects_seg_gs (0, ptr, 1);
      |                      ^~~

to:

addr-space-typeck-2.c: In function 'test_bad_call':
addr-space-typeck-2.c:12:22: error: passing argument 2 of 'expects_seg_gs'
  from pointer to non-enclosed address space
   12 |   expects_seg_gs (0, ptr, 1);
      |                      ^~~
addr-space-typeck-2.c:7:51: note: expected '__seg_gs void *' but argument
  is of type 'void *'
    7 | extern void expects_seg_gs (int i, void __seg_gs *param, int j);
      |                                    ~~~~~~~~~~~~~~~^~~~~

I took the liberty of adding the test coverage to i386 since we need
a specific target to test this on.

gcc/c/ChangeLog:
	* c-typeck.cc (build_c_cast): Quote names of address spaces in
	diagnostics.
	(convert_for_assignment): Add a note to address space mismatch
	diagnostics, specifying the expected and actual types.

gcc/testsuite/ChangeLog:
	* gcc.target/i386/addr-space-typeck-1.c: New test.
	* gcc.target/i386/addr-space-typeck-2.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

3 files changed, 66 insertions, 8 deletions

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index fd0a7f8..8514488 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -6032,18 +6032,18 @@ build_c_cast (location_t loc, tree type, tree expr)
 	  if (!addr_space_superset (as_to, as_from, &as_common))
 	    {
 	      if (ADDR_SPACE_GENERIC_P (as_from))
-		warning_at (loc, 0, "cast to %s address space pointer "
+		warning_at (loc, 0, "cast to %qs address space pointer "
 			    "from disjoint generic address space pointer",
 			    c_addr_space_name (as_to));
 
 	      else if (ADDR_SPACE_GENERIC_P (as_to))
 		warning_at (loc, 0, "cast to generic address space pointer "
-			    "from disjoint %s address space pointer",
+			    "from disjoint %qs address space pointer",
 			    c_addr_space_name (as_from));
 
 	      else
-		warning_at (loc, 0, "cast to %s address space pointer "
-			    "from disjoint %s address space pointer",
+		warning_at (loc, 0, "cast to %qs address space pointer "
+			    "from disjoint %qs address space pointer",
 			    c_addr_space_name (as_to),
 			    c_addr_space_name (as_from));
 	    }
@@ -7252,6 +7252,8 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
       if (!null_pointer_constant_p (rhs)
 	  && asr != asl && !targetm.addr_space.subset_p (asr, asl))
 	{
+	  auto_diagnostic_group d;
+	  bool diagnosed = true;
 	  switch (errtype)
 	    {
 	    case ic_argpass:
@@ -7259,7 +7261,8 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		const char msg[] = G_("passing argument %d of %qE from "
 				      "pointer to non-enclosed address space");
 		if (warnopt)
-		  warning_at (expr_loc, warnopt, msg, parmnum, rname);
+		  diagnosed
+		    = warning_at (expr_loc, warnopt, msg, parmnum, rname);
 		else
 		  error_at (expr_loc, msg, parmnum, rname);
 	      break;
@@ -7269,7 +7272,7 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		const char msg[] = G_("assignment from pointer to "
 				      "non-enclosed address space");
 		if (warnopt)
-		  warning_at (location, warnopt, msg);
+		  diagnosed = warning_at (location, warnopt, msg);
 		else
 		  error_at (location, msg);
 		break;
@@ -7280,7 +7283,7 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		const char msg[] = G_("initialization from pointer to "
 				      "non-enclosed address space");
 		if (warnopt)
-		  warning_at (location, warnopt, msg);
+		  diagnosed = warning_at (location, warnopt, msg);
 		else
 		  error_at (location, msg);
 		break;
@@ -7290,7 +7293,7 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 		const char msg[] = G_("return from pointer to "
 				      "non-enclosed address space");
 		if (warnopt)
-		  warning_at (location, warnopt, msg);
+		  diagnosed = warning_at (location, warnopt, msg);
 		else
 		  error_at (location, msg);
 		break;
@@ -7298,6 +7301,14 @@ convert_for_assignment (location_t location, location_t expr_loc, tree type,
 	    default:
 	      gcc_unreachable ();
 	    }
+	  if (diagnosed)
+	    {
+	      if (errtype == ic_argpass)
+		inform_for_arg (fundecl, expr_loc, parmnum, type, rhstype);
+	      else
+		inform (location, "expected %qT but pointer is of type %qT",
+			type, rhstype);
+	    }
 	  return error_mark_node;
 	}
 
diff --git a/gcc/testsuite/gcc.target/i386/addr-space-typeck-1.c b/gcc/testsuite/gcc.target/i386/addr-space-typeck-1.c
new file mode 100644
index 0000000..84d27b0
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/addr-space-typeck-1.c
@@ -0,0 +1,22 @@
+/* { dg-options "-std=gnu90" } */
+
+void *
+test_gs_to_generic (void __seg_gs *p)
+{
+  return p; /* { dg-error "return from pointer to non-enclosed address space" "error" } */
+  /* { dg-message "expected 'void \\*' but pointer is of type '__seg_gs void \\*'" "note" { target *-*-* } .-1 } */
+}
+
+void __seg_gs *
+test_generic_to_gs (void *q)
+{
+  return q; /* { dg-error "return from pointer to non-enclosed address space" "error" } */
+  /* { dg-message "expected '__seg_gs void \\*' but pointer is of type 'void \\*'" "note" { target *-*-* } .-1 } */
+}
+
+extern void use_double_deref (char __seg_gs **buffer);
+
+void test_double_deref (char __seg_gs *buf)
+{
+  use_double_deref (&buf);
+}
diff --git a/gcc/testsuite/gcc.target/i386/addr-space-typeck-2.c b/gcc/testsuite/gcc.target/i386/addr-space-typeck-2.c
new file mode 100644
index 0000000..d9fb9a7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/addr-space-typeck-2.c
@@ -0,0 +1,25 @@
+/* Tests of C frontend's address space type-checking.  */
+/* { dg-options "-std=gnu90 -fdiagnostics-show-caret" } */
+
+/* Verify that we emit helpful diagnostics at a mismatching address space
+   at a function call, and that the underlined locations are correct.  */
+
+extern void expects_seg_gs (int i, void __seg_gs *param, int j); /* { dg-line "decl_line" } */
+
+void
+test_bad_call (void *ptr)
+{
+  expects_seg_gs (0, ptr, 1); /* { dg-line "err_line" } */
+}
+
+/* { dg-error "passing argument 2 of 'expects_seg_gs' from pointer to non-enclosed address space" "" { target *-*-* } err_line } */
+/* { dg-begin-multiline-output "" }
+   expects_seg_gs (0, ptr, 1);
+                      ^~~
+   { dg-end-multiline-output "" } */
+
+/* { dg-message "expected '__seg_gs void \\*' but argument is of type 'void \\*'" "" { target *-*-* } decl_line } */
+/* { dg-begin-multiline-output "" }
+ extern void expects_seg_gs (int i, void __seg_gs *param, int j);
+                                    ~~~~~~~~~~~~~~~^~~~~
+   { dg-end-multiline-output "" } */