[gcc r14-9916] c++: build_extra_args recapturing local specs [PR114303]

[gcc r14-9916] c++: build_extra_args recapturing local specs [PR114303]

[Patrick Palka]

https://gcc.gnu.org/g:b262b17636e47ae969a74f16e86ccb00678d5e88

commit r14-9916-gb262b17636e47ae969a74f16e86ccb00678d5e88
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Apr 11 10:16:41 2024 -0400

    c++: build_extra_args recapturing local specs [PR114303]
    
    r13-6452-g341e6cd8d603a3 made build_extra_args walk evaluated contexts
    first so that we prefer processing a local specialization in an evaluated
    context even if its first use is in an unevaluated context.  But this
    means we need to avoid walking a tree that already has extra args/specs
    saved because the list of saved specs appears to be an evaluated
    context which we'll now walk first.  It seems then that we should be
    calculating the saved specs from scratch each time, rather than
    potentially walking the saved specs list from an earlier partial
    instantiation when calling build_extra_args a second time around.
    
            PR c++/114303
    
    gcc/cp/ChangeLog:
    
            * constraint.cc (tsubst_requires_expr): Clear
            REQUIRES_EXPR_EXTRA_ARGS before calling build_extra_args.
            * pt.cc (tree_extra_args): Define.
            (extract_locals_r): Assert *_EXTRA_ARGS is empty.
            (tsubst_stmt) <case IF_STMT>: Clear IF_SCOPE on the new
            IF_STMT.  Call build_extra_args on the new IF_STMT instead
            of t which might already have IF_STMT_EXTRA_ARGS.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1z/constexpr-if-lambda6.C: New test.
    
    Reviewed-by: Jason Merrill <jason@redhat.com>

Diff:
---
 gcc/cp/constraint.cc                              |  1 +
 gcc/cp/pt.cc                                      | 31 ++++++++++++++++++++++-
 gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C | 16 ++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 49de3211d4c..8a3b5d80ba7 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2362,6 +2362,7 @@ tsubst_requires_expr (tree t, tree args, sat_info info)
 	 matching or dguide constraint rewriting), in which case we need
 	 to partially substitute.  */
       t = copy_node (t);
+      REQUIRES_EXPR_EXTRA_ARGS (t) = NULL_TREE;
       REQUIRES_EXPR_EXTRA_ARGS (t) = build_extra_args (t, args, info.complain);
       return t;
     }
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 767778e53ef..7c91c6959aa 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3858,6 +3858,24 @@ has_extra_args_mechanism_p (const_tree t)
 	      && IF_STMT_CONSTEXPR_P (t))); /* IF_STMT_EXTRA_ARGS  */
 }
 
+/* Return *_EXTRA_ARGS of the given supported tree T.  */
+
+static tree&
+tree_extra_args (tree t)
+{
+  gcc_checking_assert (has_extra_args_mechanism_p (t));
+
+  if (PACK_EXPANSION_P (t))
+    return PACK_EXPANSION_EXTRA_ARGS (t);
+  else if (TREE_CODE (t) == REQUIRES_EXPR)
+    return REQUIRES_EXPR_EXTRA_ARGS (t);
+  else if (TREE_CODE (t) == IF_STMT
+	   && IF_STMT_CONSTEXPR_P (t))
+    return IF_STMT_EXTRA_ARGS (t);
+
+  gcc_unreachable ();
+}
+
 /* Structure used to track the progress of find_parameter_packs_r.  */
 struct find_parameter_pack_data
 {
@@ -13291,6 +13309,16 @@ extract_locals_r (tree *tp, int *walk_subtrees, void *data_)
     /* Remember local typedefs (85214).  */
     tp = &TYPE_NAME (*tp);
 
+  if (has_extra_args_mechanism_p (*tp))
+    /* Assert *_EXTRA_ARGS is empty, because we don't want to walk it and
+       potentially see a previously captured local in an evaluated context
+       that's really only used in an unevaluated context (PR114303).  This
+       means callers of build_extra_args need to clear *_EXTRA_ARGS of the
+       outermost tree.  Nested *_EXTRA_ARGS should naturally be empty since
+       the outermost (extra-args) tree will intercept any substitution before
+       a nested tree can.  */
+    gcc_checking_assert (tree_extra_args (*tp) == NULL_TREE);
+
   if (TREE_CODE (*tp) == DECL_EXPR)
     {
       tree decl = DECL_EXPR_DECL (*tp);
@@ -18716,10 +18744,11 @@ tsubst_stmt (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	     of the constexpr if is still dependent.  Don't substitute into the
 	     branches now, just remember the template arguments.  */
 	  do_poplevel (IF_SCOPE (stmt));
+	  IF_SCOPE (stmt) = NULL_TREE;
 	  IF_COND (stmt) = IF_COND (t);
 	  THEN_CLAUSE (stmt) = THEN_CLAUSE (t);
 	  ELSE_CLAUSE (stmt) = ELSE_CLAUSE (t);
-	  IF_STMT_EXTRA_ARGS (stmt) = build_extra_args (t, args, complain);
+	  IF_STMT_EXTRA_ARGS (stmt) = build_extra_args (stmt, args, complain);
 	  add_stmt (stmt);
 	  break;
 	}
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C
new file mode 100644
index 00000000000..038c2a41210
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if-lambda6.C
@@ -0,0 +1,16 @@
+// PR c++/114303
+// { dg-do compile { target c++17 } }
+
+struct A { static constexpr bool value = true; };
+
+int main() {
+  [](auto x1) {
+    return [&](auto) {
+      return [&](auto x3) {
+        if constexpr (decltype(x3)::value) {
+          static_assert(decltype(x1)::value);
+        }
+      }(A{});
+    }(0);
+  }(A{});
+}