On 3/25/25 11:43 AM, yxj-github-437 wrote:
This patch would like to avoid the ICE when template lambdas call with
default parameters in unevaluated context. The bug is the same as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119385. For example as blow:
1 | template <class T>
2 | void foo(T x) {
3 | sizeof []<int=0>(T=x) { return 0; }();
4 | }
5 |
6 | void test {
7 | foo(0);
8 | }
when compile with -fsyntax-only -std=c++20, it will have ICE similar as below
test.cc: In instantiation of 'void foo(T) [with T = int]':
test.cc:7:6: required from here
6 | foo(0);
| ~~~^~~
test.cc:3:38: internal compiler error: in tsubst_expr, at cp/pt.cc:21919
2 | sizeof []<int=0>(T=x) { return 0; }();
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
And if without the template code `<int=0>`, the code will pass compile, it's
wrong.
When parsing lambda, the sizeof will affect the lambda internal unevaluated
operand
being handled. So consider save/restore cp_unevaluated_operand.
gcc/cp/ChangeLog:
* parser.cc (cp_parser_lambda_expression): Save/restore
cp_unevaluated_operand when parser lambda.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/lambda-uneval25.C: New test.
---
gcc/cp/parser.cc | 4 ++++
gcc/testsuite/g++.dg/cpp2a/lambda-uneval25.C | 11 +++++++++++
2 files changed, 15 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval25.C
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 57a461042bf..9cc51f57fa7 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -11754,6 +11754,8 @@ cp_parser_lambda_expression (cp_parser* parser)
/* Inside the class, surrounding template-parameter-lists do not apply.
*/
unsigned int saved_num_template_parameter_lists
= parser->num_template_parameter_lists;
+ /* Inside the lambda, outside unevaluated context do not apply. */
+ int saved_cp_unevaluated_operand = cp_unevaluated_operand;
Instead of following the surrounding pattern, please use cp_evaluated.
That avoids the need for any change in the other two places.
OK, I've replace it with cp_evaluated.
Pushed, thanks. I removed an extra space in the comment and adjusted
the commit message to fit in 75 columns.
Jason
