[gcc r15-10887] c++: Fix wrong-code with overloaded comma and CPP_EMBED [PR123737]

[Jakub Jelinek]

https://gcc.gnu.org/g:c8637cd2eea50953208a12a5c7a638b92357612a

commit r15-10887-gc8637cd2eea50953208a12a5c7a638b92357612a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jan 24 10:38:17 2026 +0100

    c++: Fix wrong-code with overloaded comma and CPP_EMBED [PR123737]
    
    In cp_parser_expression for comma operator I've used a short path
    where instead of calling build_x_compound_expr #embed number times
    it is called just 3 times, for the CPP_NUMBER added by the preprocessor
    at the start, last byte from CPP_EMBED and then CPP_NUMBER added by
    libcpp at the end, enough to make sure -Wunused-value reports something,
    but not bothering users with millions of -Wunused-value warnings
    and spending too much compile time on it when they use a very large #embed.
    
    As the following testcases show, that is ok for C or for C++ if the
    expression before it is known not to have OVERLOAD_TYPE_P (common case
    is INTEGER_TYPE I guess), but doesn't work well in case one uses overloaded
    comma operator.  In that case we just have to call build_x_compound_expr
    the right number of times, even if it is a lot.
    
    I think I don't need to test for !expression, because the preprocessor
    should guarantee that CPP_EMBED is preceded by CPP_NUMBER CPP_COMMA
    tokens.
    
    2026-01-24  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/123737
            * parser.cc (cp_parser_expression): Don't handle CPP_EMBED just
            as the last byte in it if expression has or might have overloaded
            type.  In that case call build_x_compound_expr for each byte
            in CPP_EMBED separately.
    
            * g++.dg/cpp/embed-28.C: New test.
            * g++.dg/parse/comma3.C: New test.
    
    (cherry picked from commit e2f626b37ef62fcab8667b2a67318c27a8f2a6ca)

Diff:
---
 gcc/cp/parser.cc                    | 16 +++++++++++++++-
 gcc/testsuite/g++.dg/cpp/embed-28.C | 19 +++++++++++++++++++
 gcc/testsuite/g++.dg/parse/comma3.C | 22 ++++++++++++++++++++++
 3 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 317901bb1691..b777cad0ec3c 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -11268,10 +11268,24 @@ cp_parser_expression (cp_parser* parser, cp_id_kind * pidk,
 	     and one CPP_NUMBER plus CPP_COMMA before it and one
 	     CPP_COMMA plus CPP_NUMBER after it is guaranteed by
 	     the preprocessor.  Thus, parse the whole CPP_EMBED just
-	     as a single INTEGER_CST, the last byte in it.  */
+	     as a single INTEGER_CST, the last byte in it.  Though,
+	     don't use that shortcut if the comma operator could be
+	     overloaded.  */
 	  tree raw_data = cp_lexer_peek_token (parser->lexer)->u.value;
 	  location_t loc = cp_lexer_peek_token (parser->lexer)->location;
 	  cp_lexer_consume_token (parser->lexer);
+	  if (OVERLOAD_TYPE_P (TREE_TYPE (expression))
+	      || type_dependent_expression_p (expression))
+	    for (unsigned i = 0; i < RAW_DATA_LENGTH (raw_data) - 1U; ++i)
+	      {
+		assignment_expression
+		  = *raw_data_iterator (raw_data, i);
+		assignment_expression.set_location (loc);
+		expression
+		  = build_x_compound_expr (loc, expression,
+					   assignment_expression, NULL_TREE,
+					   complain_flags (decltype_p));
+	      }
 	  assignment_expression
 	    = *raw_data_iterator (raw_data, RAW_DATA_LENGTH (raw_data) - 1);
 	  assignment_expression.set_location (loc);
diff --git a/gcc/testsuite/g++.dg/cpp/embed-28.C b/gcc/testsuite/g++.dg/cpp/embed-28.C
new file mode 100644
index 000000000000..0d8d1adf6377
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp/embed-28.C
@@ -0,0 +1,19 @@
+// PR c++/123737
+// { dg-do run }
+// { dg-options "--embed-dir=${srcdir}/c-c++-common/cpp/embed-dir" }
+
+struct A {
+  A (int x) : a (0), e (x) {}
+  unsigned long a, e;
+  A &operator, (int) { ++a; return *this; }
+  ~A () { if (a != e) __builtin_abort (); }
+};
+
+int
+main ()
+{
+  A a = 231;
+  a,
+#embed <magna-carta.txt> limit (231)
+    ;
+}
diff --git a/gcc/testsuite/g++.dg/parse/comma3.C b/gcc/testsuite/g++.dg/parse/comma3.C
new file mode 100644
index 000000000000..71603d3315a7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/comma3.C
@@ -0,0 +1,22 @@
+// PR c++/123737
+// { dg-do run }
+
+struct A {
+  A (int x) : a (0), e (x) {}
+  unsigned long a, e;
+  A &operator, (int) { ++a; return *this; }
+  ~A () { if (a != e) __builtin_abort (); }
+};
+
+int
+main ()
+{
+  A a = 131;
+  a, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0;
+}