[gcc r12-5054] c++: Fix ICE on complex constant with -frounding-math [PR103114]

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

https://gcc.gnu.org/g:0318df0ae63e47f6b2f30e96205d00dcb3696538

commit r12-5054-g0318df0ae63e47f6b2f30e96205d00dcb3696538
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Nov 9 15:29:36 2021 +0100

    c++: Fix ICE on complex constant with -frounding-math [PR103114]
    
    The FE uses build_complex which assumes that fold_convert will fold
    value to a constant.  With -frounding-math that isn't guaranteed though.
    So, the patch instead fold_build2s COMPLEX_EXPR, which will result
    in build_complex if both arguments are constants, and otherwise
    will build COMPLEX_EXPR.
    build_zero_cst is an optimization for fold_convert (type, integer_zero_node).
    
    2021-11-09  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/103114
            * parser.c (cp_parser_userdef_numeric_literal): Use fold_build2
            with COMPLEX_EXPR arg instead of build_complex, use build_zero_cst
            instead of fold_convert from integer_zero_node.
    
            * g++.dg/ext/complex10.C: New test.

Diff:
---
 gcc/cp/parser.c                      | 5 ++---
 gcc/testsuite/g++.dg/ext/complex10.C | 5 +++++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 6061f983392..32de97b08bd 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -4804,9 +4804,8 @@ cp_parser_userdef_numeric_literal (cp_parser *parser)
       else /* if (id_equal (suffix_id, "il")) */
 	type = long_double_type_node;
 
-      value = build_complex (build_complex_type (type),
-			     fold_convert (type, integer_zero_node),
-			     fold_convert (type, value));
+      value = fold_build2 (COMPLEX_EXPR, build_complex_type (type),
+			   build_zero_cst (type), fold_convert (type, value));
     }
 
   if (cp_parser_uncommitted_to_tentative_parse_p (parser))
diff --git a/gcc/testsuite/g++.dg/ext/complex10.C b/gcc/testsuite/g++.dg/ext/complex10.C
new file mode 100644
index 00000000000..67dfb0c2aed
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/complex10.C
@@ -0,0 +1,5 @@
+// PR c++/103114
+// { dg-do compile }
+// { dg-options "-frounding-math" }
+
+_Complex double d = 10.1i;