[gcc r16-1992] c++: trivial lambda pruning [PR120716]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:387cc9f80fcfd8b7d3fc142ef01bb05a46f0f244

commit r16-1992-g387cc9f80fcfd8b7d3fc142ef01bb05a46f0f244
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Jul 3 16:52:56 2025 -0400

    c++: trivial lambda pruning [PR120716]
    
    In this testcase there is nothing in the lambda except a static_assert which
    mentions a variable from the enclosing scope but does not odr-use it, so we
    want prune_lambda_captures to remove its capture.  Since the lambda is so
    empty, there's nothing in the body except the DECL_EXPR of the capture
    proxy, so pop_stmt_list moves that into the enclosing STATEMENT_LIST and
    passes the 'body' STATEMENT_LIST to free_stmt_list.  As a result, passing
    'body' to prune_lambda_captures is wrong; we should instead pass the
    enclosing scope, i.e. cur_stmt_list.
    
            PR c++/120716
    
    gcc/cp/ChangeLog:
    
            * lambda.cc (finish_lambda_function): Pass cur_stmt_list to
            prune_lambda_captures.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/lambda/lambda-constexpr3.C: New test.
            * g++.dg/cpp0x/lambda/lambda-constexpr3a.C: New test.

Diff:
---
 gcc/cp/lambda.cc                                       |  2 +-
 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3.C  | 13 +++++++++++++
 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3a.C | 12 ++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/lambda.cc b/gcc/cp/lambda.cc
index ae732c3f72a6..182cffaf8d4f 100644
--- a/gcc/cp/lambda.cc
+++ b/gcc/cp/lambda.cc
@@ -1950,7 +1950,7 @@ finish_lambda_function (tree body)
 {
   finish_function_body (body);
 
-  prune_lambda_captures (body);
+  prune_lambda_captures (cur_stmt_list);
 
   /* Finish the function and generate code for it if necessary.  */
   tree fn = finish_function (/*inline_p=*/true);
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3.C 
b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3.C
new file mode 100644
index 000000000000..652521325f68
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3.C
@@ -0,0 +1,13 @@
+// PR c++/120716
+// { dg-do compile { target c++11 } }
+
+struct A { int *r; };
+
+void
+foo ()
+{
+  static int i;
+  constexpr A a = { &i };
+  static_assert (a.r == &i, "");
+  [&] { static_assert (a.r != nullptr, ""); } ();
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3a.C 
b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3a.C
new file mode 100644
index 000000000000..398e079f7246
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-constexpr3a.C
@@ -0,0 +1,12 @@
+// PR c++/120716
+// { dg-do compile { target c++11 } }
+
+struct A { int *const &r; };
+
+void
+foo (int x)
+{
+  constexpr A a = { &x };      // { dg-error "constant" }
+  static_assert (a.r == &x, "");       // { dg-error "non-constant" }
+  [&] { static_assert (a.r != nullptr, ""); } (); // { dg-error "non-constant" 
}
+}