Re: [PATCH] c++: partially inst requires-expr in noexcept-spec [PR101043]

[Jason Merrill]

On 11/14/23 16:04, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

OK.

-- >8 --

Here we're ICEing from strip_typedefs for the partially instantiated
requires-expression when walking its REQUIRES_EXPR_EXTRA_ARGS since it's
a TREE_LIST with non-empty TREE_PURPOSE (to hold the captured local
specialization 't' as per build_extra_args) which strip_typedefs doesn't
expect.

We can probably skip walking REQUIRES_EXPR_EXTRA_ARGS at all since it
shouldn't contain any typedefs in the first place, but it seems safer
and more generally useful to just teach strip_typedefs to handle non-empty
TREE_PURPOSE the obvious way.  (The handling asserted TREE_PURPOSE was
empty ever since inception i.e. r189298.)

        PR c++/101043

gcc/cp/ChangeLog:

        * tree.cc (strip_typedefs_expr) <case TREE_LIST>: Handle
        non-empty TREE_PURPOSE.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/concepts-requires37.C: New test.
---
  gcc/cp/tree.cc                                | 19 ++++++++++++-------
  .../g++.dg/cpp2a/concepts-requires37.C        | 11 +++++++++++
  2 files changed, 23 insertions(+), 7 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index dc4126f935c..0736e8d8f48 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1911,19 +1911,24 @@ strip_typedefs_expr (tree t, bool *remove_attributes, 
unsigned int flags)
      case TREE_LIST:
        {
        bool changed = false;
-       releasing_vec vec;
+       auto_vec<tree_pair, 4> vec;
        r = t;
        for (; t; t = TREE_CHAIN (t))
          {
-           gcc_assert (!TREE_PURPOSE (t));
-           tree elt = strip_typedefs (TREE_VALUE (t),
-                                      remove_attributes, flags);
-           if (elt != TREE_VALUE (t))
+           tree purpose = strip_typedefs (TREE_PURPOSE (t),
+                                          remove_attributes, flags);
+           tree value = strip_typedefs (TREE_VALUE (t),
+                                        remove_attributes, flags);
+           if (purpose != TREE_PURPOSE (t) || value != TREE_VALUE (t))
              changed = true;
-           vec_safe_push (vec, elt);
+           vec.safe_push ({purpose, value});
          }
        if (changed)
-         r = build_tree_list_vec (vec);
+         {
+           r = NULL_TREE;
+           for (int i = vec.length () - 1; i >= 0; i--)
+             r = tree_cons (vec[i].first, vec[i].second, r);
+         }
        return r;
        }

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C

new file mode 100644
index 00000000000..72dad77fea1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
@@ -0,0 +1,11 @@
+// PR c++/101043
+// { dg-do compile { target c++20 } }
+
+template<class T>
+void f(T t) {
+  [&](auto) noexcept(requires { { t.g() }; }) { }(0);
+}
+
+int main() {
+  f(0);
+}