From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Sun, 13 Apr 2025 02:20:37 +0000 (+1000)
Subject: c++: Prune lambda captures from more places [PR119755]
X-Git-Tag: basepoints/gcc-16~45
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a6f4178d0d5a51c0de175d282f693f923ffefa27;p=thirdparty%2Fgcc.git

c++: Prune lambda captures from more places [PR119755]

Currently, pruned lambda captures are still leftover in the function's
BLOCK and topmost BIND_EXPR; this doesn't cause any issues for normal
compilation, but does break modules streaming as we try to reconstruct a
FIELD_DECL that no longer exists on the type itself.

	PR c++/119755

gcc/cp/ChangeLog:

	* lambda.cc (prune_lambda_captures): Remove pruned capture from
	function's BLOCK_VARS and BIND_EXPR_VARS.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/lambda-10_a.H: New test.
	* g++.dg/modules/lambda-10_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index f0a54b60275..b2e0ecdd67e 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -1858,6 +1858,13 @@ prune_lambda_captures (tree body)
 
   cp_walk_tree_without_duplicates (&body, mark_const_cap_r, &const_vars);
 
+  tree bind_expr = expr_single (DECL_SAVED_TREE (lambda_function (lam)));
+  if (bind_expr && TREE_CODE (bind_expr) == MUST_NOT_THROW_EXPR)
+    bind_expr = expr_single (TREE_OPERAND (bind_expr, 0));
+  /* FIXME: We don't currently handle noexcept lambda captures correctly,
+     so bind_expr may not be set; see PR c++/119764.  */
+  gcc_assert (!bind_expr || TREE_CODE (bind_expr) == BIND_EXPR);
+
   tree *fieldp = &TYPE_FIELDS (LAMBDA_EXPR_CLOSURE (lam));
   for (tree *capp = &LAMBDA_EXPR_CAPTURE_LIST (lam); *capp; )
     {
@@ -1879,6 +1886,23 @@ prune_lambda_captures (tree body)
 		fieldp = &DECL_CHAIN (*fieldp);
 	      *fieldp = DECL_CHAIN (*fieldp);
 
+	      /* And out of the bindings for the function.  */
+	      tree *blockp = &BLOCK_VARS (current_binding_level->blocks);
+	      while (*blockp != DECL_EXPR_DECL (**use))
+		blockp = &DECL_CHAIN (*blockp);
+	      *blockp = DECL_CHAIN (*blockp);
+
+	      /* And maybe out of the vars declared in the containing
+		 BIND_EXPR, if it's listed there.  */
+	      if (bind_expr)
+		{
+		  tree *bindp = &BIND_EXPR_VARS (bind_expr);
+		  while (*bindp && *bindp != DECL_EXPR_DECL (**use))
+		    bindp = &DECL_CHAIN (*bindp);
+		  if (*bindp)
+		    *bindp = DECL_CHAIN (*bindp);
+		}
+
 	      /* And remove the capture proxy declaration.  */
 	      **use = void_node;
 	      continue;
diff --git a/gcc/testsuite/g++.dg/modules/lambda-10_a.H b/gcc/testsuite/g++.dg/modules/lambda-10_a.H
new file mode 100644
index 00000000000..1ad1a808c07
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-10_a.H
@@ -0,0 +1,17 @@
+// PR c++/119755
+// { dg-additional-options "-fmodule-header" }
+// { dg-module-cmi {} }
+
+template <typename _Out> void format(_Out) {
+  constexpr int __term = 1;
+  [&] { __term; };
+  [&] { const int outer = __term; { __term; } };
+  [&]() noexcept { __term; };
+  [&]() noexcept { const int outer = __term; { __term; } };
+  [&](auto) { int n[__term]; }(0);
+  [&](auto) noexcept { int n[__term]; }(0);
+}
+
+inline void vformat() {
+  format(0);
+}
diff --git a/gcc/testsuite/g++.dg/modules/lambda-10_b.C b/gcc/testsuite/g++.dg/modules/lambda-10_b.C
new file mode 100644
index 00000000000..3556bcee02c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/lambda-10_b.C
@@ -0,0 +1,7 @@
+// PR c++/119755
+// { dg-additional-options "-fmodules" }
+
+import "lambda-10_a.H";
+int main() {
+  vformat();
+}