[gcc r10-10605] c++: ICE with requires-expr and -Wsequence-point [PR105304]

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:9a8b7edbe65ec6350a996eab51a7c26a087e6d2b

commit r10-10605-g9a8b7edbe65ec6350a996eab51a7c26a087e6d2b
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Apr 25 21:49:00 2022 -0400

    c++: ICE with requires-expr and -Wsequence-point [PR105304]
    
    Here we're crashing from verify_sequence_points for this requires-expr
    condition because it contains a templated CAST_EXPR with empty operand,
    and verify_tree doesn't ignore this empty operand only because the
    manual tail recursion that it performs for unary expression trees skips
    the NULL test.
    
            PR c++/105304
    
    gcc/c-family/ChangeLog:
    
            * c-common.c (verify_tree) [restart]: Move up to before the
            NULL test.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-requires30.C: New test.
    
    (cherry picked from commit c83b9c54d9dee2dce5d8268472a745b013d166cc)

Diff:
---
 gcc/c-family/c-common.c                          |  2 +-
 gcc/testsuite/g++.dg/cpp2a/concepts-requires30.C | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 064c2f263f0..661a194fc89 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -1838,12 +1838,12 @@ verify_tree (tree x, struct tlist **pbefore_sp, struct tlist **pno_sp,
   enum tree_code code;
   enum tree_code_class cl;
 
+ restart:
   /* X may be NULL if it is the operand of an empty statement expression
      ({ }).  */
   if (x == NULL)
     return;
 
- restart:
   code = TREE_CODE (x);
   cl = TREE_CODE_CLASS (code);
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires30.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires30.C
new file mode 100644
index 00000000000..f500af3f616
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires30.C
@@ -0,0 +1,10 @@
+// PR c++/105304
+// { dg-do compile { target c++20 } }
+// { dg-additional-options "-Wall -Wsequence-point" }
+
+struct A { };
+
+int main() {
+  if (requires { A(); })
+    ;
+}