[gcc r12-11224] lto/114501 - missed free-lang-data for CONSTRUCTOR index

[Richard Biener]

https://gcc.gnu.org/g:415bad120d8f21cd754d827da9e3d5e1fbe68d4c

commit r12-11224-g415bad120d8f21cd754d827da9e3d5e1fbe68d4c
Author: Richard Biener <rguenther@suse.de>
Date:   Thu Mar 6 13:48:16 2025 +0100

    lto/114501 - missed free-lang-data for CONSTRUCTOR index
    
    The following makes sure to also walk CONSTRUCTOR element indexes
    which can be FIELD_DECLs, referencing otherwise unused types we
    need to clean.  walk_tree only walks CONSTRUCTOR element data.
    
            PR lto/114501
            * ipa-free-lang-data.cc (find_decls_types_r): Explicitly
            handle CONSTRUCTORs as walk_tree handling of those is
            incomplete.
    
            * g++.dg/pr114501_0.C: New testcase.
    
    (cherry picked from commit fdd95e1cf29137a19baed25f8c817d320dfe63e3)

Diff:
---
 gcc/ipa-free-lang-data.cc         | 14 ++++++++++++++
 gcc/testsuite/g++.dg/pr114501_0.C | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/gcc/ipa-free-lang-data.cc b/gcc/ipa-free-lang-data.cc
index 6fef047e3beb..1bfa0239be51 100644
--- a/gcc/ipa-free-lang-data.cc
+++ b/gcc/ipa-free-lang-data.cc
@@ -841,6 +841,20 @@ find_decls_types_r (tree *tp, int *ws, void *data)
 	fld_worklist_push (tem, fld);
       fld_worklist_push (BLOCK_ABSTRACT_ORIGIN (t), fld);
     }
+  /* walk_tree does not visit ce->index which can be a FIELD_DECL, pulling
+     in otherwise unused structure fields so handle CTORs explicitly.  */
+  else if (TREE_CODE (t) == CONSTRUCTOR)
+    {
+      unsigned HOST_WIDE_INT idx;
+      constructor_elt *ce;
+      for (idx = 0; vec_safe_iterate (CONSTRUCTOR_ELTS (t), idx, &ce); idx++)
+	{
+	  if (ce->index)
+	    fld_worklist_push (ce->index, fld);
+	  fld_worklist_push (ce->value, fld);
+	}
+      *ws = 0;
+    }
 
   if (TREE_CODE (t) != IDENTIFIER_NODE
       && CODE_CONTAINS_STRUCT (TREE_CODE (t), TS_TYPED))
diff --git a/gcc/testsuite/g++.dg/pr114501_0.C b/gcc/testsuite/g++.dg/pr114501_0.C
new file mode 100644
index 000000000000..0439ee5f6e23
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr114501_0.C
@@ -0,0 +1,20 @@
+// { dg-do compile }
+// { dg-require-effective-target c++17 }
+// { dg-require-effective-target lto }
+// { dg-options "-flto" }
+
+typedef long unsigned int size_t;
+struct basic_string_view {
+  typedef long unsigned int size_type;
+  constexpr size_type size() const { return 0; }
+};
+struct array {
+  char _M_elems[1];
+};
+inline constexpr auto make_it() {
+  constexpr basic_string_view view;
+  array arr{};
+  arr._M_elems[view.size()] = 'a';
+  return arr;
+}
+auto bar = make_it();