From 6441bc34bcd4cc558d79710a87c2ab47085a8712 Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Thu, 19 Feb 2026 12:40:39 -0500
Subject: [PATCH] c++/reflection: also walk BIND_EXPR_BODY

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.  For
	IF_STMT_CONSTEXPR_P, only walk the THEN_ and ELSE_CLAUSE.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/expr11.C: Test more if constexpr.
	* g++.dg/reflect/expr12.C: Adjust test.

Reviewed-by: Jason Merrill <jason@redhat.com>
---
 gcc/cp/reflect.cc                     | 42 +++++++++++++++++++++++++--
 gcc/testsuite/g++.dg/reflect/expr11.C | 17 +++++++++++
 gcc/testsuite/g++.dg/reflect/expr12.C | 18 ++++++++++++
 3 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
index 5254ac028d1..3c82251f511 100644
--- a/gcc/cp/reflect.cc
+++ b/gcc/cp/reflect.cc
@@ -8120,8 +8120,6 @@ 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)
     {
@@ -8151,6 +8149,46 @@ 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 (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;
+	}
+      else if (IF_STMT_CONSTEXPR_P (t))
+	{
+	  if (tree r = cp_walk_tree (&THEN_CLAUSE (t),
+				     check_out_of_consteval_use_r, pset,
+				     static_cast<hash_set<tree> *>(pset)))
+	    return r;
+	  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 condition -- it's a manifestly constant-evaluated
+	     context.  */
+	  *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..44d66947d9d 100644
--- a/gcc/testsuite/g++.dg/reflect/expr11.C
+++ b/gcc/testsuite/g++.dg/reflect/expr11.C
@@ -29,4 +29,21 @@ f ()
     while (^^char != ^^char);
     do {} while (^^char != ^^char);
   }
+
+  if constexpr (true)
+    {
+      auto r = ^^int; // { dg-error "consteval-only variable .r." }
+    }
+  else
+    {
+      auto r = ^^int; // { dg-error "consteval-only variable .r." }
+    }
+  if constexpr (false)
+    {
+      auto r = ^^int; // { dg-error "consteval-only variable .r." }
+    }
+  else
+    {
+      auto r = ^^int; // { dg-error "consteval-only variable .r." }
+    }
 }
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" }
     }
 }