[gcc r10-10699] c++: Fix up __builtin_convertvector parsing

[Jakub Jelinek <jakub@gcc.gnu.org>]

https://gcc.gnu.org/g:91cc882245d7d93876d34f4d4c2e425acf48c8bb

commit r10-10699-g91cc882245d7d93876d34f4d4c2e425acf48c8bb
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Mar 26 08:11:58 2022 +0100

    c++: Fix up __builtin_convertvector parsing
    
    Jonathan reported on IRC that we don't parse
    __builtin_bit_cast (type, val).field
    etc.
    The problem is that for these 2 builtins we return from
    cp_parser_postfix_expression instead of setting postfix_expression
    to the cp_build_* value and falling through into the postfix regression
    suffix handling loop.
    
    2022-03-26  Jakub Jelinek  <jakub@redhat.com>
    
            * parser.c (cp_parser_postfix_expression)
            <case RID_BILTIN_CONVERTVECTOR>: Don't
            return cp_build_vec_convert result right away, instead
            set postfix_expression to it and break.
    
            * c-c++-common/builtin-convertvector-3.c: New test.
    
    (cherry picked from commit 1806829e08f14e4cacacec43d7845cc2dad2ddc8)

Diff:
---
 gcc/cp/parser.c                                      |  6 ++++--
 gcc/testsuite/c-c++-common/builtin-convertvector-3.c | 11 +++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index f48c856fa94..61f2af34688 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7162,8 +7162,10 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
 	}
 	/* Look for the closing `)'.  */
 	parens.require_close (parser);
-	return cp_build_vec_convert (expression, type_location, type,
-				     tf_warning_or_error);
+	postfix_expression
+	  = cp_build_vec_convert (expression, type_location, type,
+				  tf_warning_or_error);
+	break;
       }
 
     default:
diff --git a/gcc/testsuite/c-c++-common/builtin-convertvector-3.c b/gcc/testsuite/c-c++-common/builtin-convertvector-3.c
new file mode 100644
index 00000000000..882cd551ef8
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/builtin-convertvector-3.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef int v4si __attribute__((vector_size (4 * sizeof (int))));
+typedef double v4df __attribute__((vector_size (4 * sizeof (double))));
+double
+foo (void)
+{
+  v4si a = { 1, 2, 3, 4 };
+  return __builtin_convertvector (a, v4df)[1];
+}