dg.exp=reflect/* passed on x86_64-linux so far.  Ok for trunk?

-- >8 --
As discussed in
<https://gcc.gnu.org/pipermail/gcc-patches/2026-January/705756.html>,
we shouldn't walk BIND_EXPR_VARS in check_out_of_consteval_use_r, but
BIND_EXPR_BODY should still be walked.

The IF_STMT is there so that we don't emit bogus errors in "if consteval"
branches, as tested in expr12.C.

gcc/cp/ChangeLog:

        * reflect.cc (check_out_of_consteval_use_r): Walk BIND_EXPR_BODY.
        For IF_STMT_CONSTEVAL_P, only walk the ELSE_CLAUSE.

gcc/testsuite/ChangeLog:

        * g++.dg/reflect/expr11.C: Adjust dg-error.
        * g++.dg/reflect/expr12.C: Adjust test.
---
 gcc/cp/reflect.cc                     | 24 ++++++++++++++++++++++--
 gcc/testsuite/g++.dg/reflect/expr11.C |  2 +-
 gcc/testsuite/g++.dg/reflect/expr12.C | 18 ++++++++++++++++++
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
index 46355251bcd..0e9118129be 100644
--- a/gcc/cp/reflect.cc
+++ b/gcc/cp/reflect.cc
@@ -8108,8 +8108,6 @@ check_out_of_consteval_use_r (tree *tp, int 
*walk_subtrees, void *pset)
       /* Don't walk INIT_EXPRs, because we'd emit bogus errors about
         member initializers.  */
       || TREE_CODE (t) == INIT_EXPR
-      /* Don't walk BIND_EXPR_VARS.  */
-      || TREE_CODE (t) == BIND_EXPR
       /* And don't recurse on DECL_EXPRs.  */
       || TREE_CODE (t) == DECL_EXPR)
     {
@@ -8139,6 +8137,28 @@ check_out_of_consteval_use_r (tree *tp, int 
*walk_subtrees, void *pset)
        return ret;
     }
 
+  if (TREE_CODE (t) == BIND_EXPR)
+    {
+      if (tree r = cp_walk_tree (&BIND_EXPR_BODY (t),
+                                check_out_of_consteval_use_r, pset,
+                                static_cast<hash_set<tree> *>(pset)))
+       return r;
+      /* Don't walk BIND_EXPR_VARS.  */
+      *walk_subtrees = false;
+      return NULL_TREE;
+    }
+
+  if (TREE_CODE (t) == IF_STMT && IF_STMT_CONSTEVAL_P (t))
+    {
+      if (tree r = cp_walk_tree (&ELSE_CLAUSE (t),
+                                check_out_of_consteval_use_r, pset,
+                                static_cast<hash_set<tree> *>(pset)))
+       return r;
+      /* Don't walk the consteval branch.  */
+      *walk_subtrees = false;
+      return NULL_TREE;
+    }
+
   /* Now check the type to see if we are dealing with a consteval-only
      expression.  */
   if (!consteval_only_p (t))
diff --git a/gcc/testsuite/g++.dg/reflect/expr11.C 
b/gcc/testsuite/g++.dg/reflect/expr11.C
index 20af4bc07ae..9691ceb07c7 100644
--- a/gcc/testsuite/g++.dg/reflect/expr11.C
+++ b/gcc/testsuite/g++.dg/reflect/expr11.C
@@ -15,7 +15,7 @@ f ()
       constexpr auto cr = ^^int;
     }
   if constexpr (auto r = ^^int;  // { dg-error "consteval-only variable .r." }
-               r == ^^int);     // { dg-error "the value of .r. is not usable" 
}
+               r == ^^int);     // { dg-error "consteval-only expressions|the 
value of .r. is not usable" }
   if constexpr (constexpr auto r = ^^int; r == ^^int);
   if constexpr (q != ^^char);
   if constexpr (^^int != ^^char);
diff --git a/gcc/testsuite/g++.dg/reflect/expr12.C 
b/gcc/testsuite/g++.dg/reflect/expr12.C
index a59a60f03a3..34aed536429 100644
--- a/gcc/testsuite/g++.dg/reflect/expr12.C
+++ b/gcc/testsuite/g++.dg/reflect/expr12.C
@@ -20,11 +20,29 @@ f ()
   if not consteval
     {
       ^^void;  // { dg-error "consteval-only expressions" }
+    }
+  if not consteval
+    {
       q;  // { dg-error "consteval-only expressions" }
+    }
+  if not consteval
+    {
       auto r = ^^int;  // { dg-error "consteval-only variable" }
+    }
+  if not consteval
+    {
       if (q != ^^char);  // { dg-error "consteval-only expressions" }
+    }
+  if not consteval
+    {
       if (^^char == ^^char);  // { dg-error "consteval-only expressions" }
+    }
+  if not consteval
+    {
       while (^^char != ^^char);  // { dg-error "consteval-only expressions" }
+    }
+  if not consteval
+    {
       do {} while (^^char != ^^char);  // { dg-error "consteval-only 
expressions" }
     }
 }

base-commit: 918cf3a50de02334af7bac2ad11ac89e8d816c11
-- 
2.53.0

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