[gcc r9-9447] c++: Fix up handling of structured bindings in extract_locals_r [PR99833]

[gcc r9-9447] c++: Fix up handling of structured bindings in extract_locals_r [PR99833]

[Jakub Jelinek]

https://gcc.gnu.org/g:969999f7b35903338738c7e7e4d99aa929276404

commit r9-9447-g969999f7b35903338738c7e7e4d99aa929276404
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Apr 16 09:32:44 2021 +0200

    c++: Fix up handling of structured bindings in extract_locals_r [PR99833]
    
    The following testcase ICEs in tsubst_decomp_names because the assumptions
    that the structured binding artificial var is followed in DECL_CHAIN by
    the corresponding structured binding vars is violated.
    I've tracked it to extract_locals* which is done for the constexpr
    IF_STMT.  extract_locals_r when it sees a DECL_EXPR adds that decl
    into a hash set so that such decls aren't returned from extract_locals*,
    but in the case of a structured binding that just means the artificial var
    and not the vars corresponding to structured binding identifiers.
    The following patch fixes it by pushing not just the artificial var
    for structured bindings but also the other vars.
    
    2021-04-16  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/99833
            * pt.c (extract_locals_r): When handling DECL_EXPR of a structured
            binding, add to data.internal also all corresponding structured
            binding decls.
    
            * g++.dg/cpp1z/pr99833.C: New test.
    
    (cherry picked from commit 06d50ebc9fb2761ed2bdda5e76adb4d47a8ca983)

Diff:
---
 gcc/cp/pt.c                          | 22 +++++++++++++++++++++-
 gcc/testsuite/g++.dg/cpp1z/pr99833.C | 11 +++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 86b13f9d2bd..104b228187e 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12104,7 +12104,27 @@ extract_locals_r (tree *tp, int */*walk_subtrees*/, void *data_)
     tp = &TYPE_NAME (*tp);
 
   if (TREE_CODE (*tp) == DECL_EXPR)
-    data.internal.add (DECL_EXPR_DECL (*tp));
+    {
+      tree decl = DECL_EXPR_DECL (*tp);
+      data.internal.add (decl);
+      if (VAR_P (decl)
+	  && DECL_DECOMPOSITION_P (decl)
+	  && TREE_TYPE (decl) != error_mark_node)
+	{
+	  gcc_assert (DECL_NAME (decl) == NULL_TREE);
+	  for (tree decl2 = DECL_CHAIN (decl);
+	       decl2
+	       && VAR_P (decl2)
+	       && DECL_DECOMPOSITION_P (decl2)
+	       && DECL_NAME (decl2)
+	       && TREE_TYPE (decl2) != error_mark_node;
+	       decl2 = DECL_CHAIN (decl2))
+	    {
+	      gcc_assert (DECL_DECOMP_BASE (decl2) == decl);
+	      data.internal.add (decl2);
+	    }
+	}
+    }
   else if (tree spec = retrieve_local_specialization (*tp))
     {
       if (data.internal.contains (*tp))
diff --git a/gcc/testsuite/g++.dg/cpp1z/pr99833.C b/gcc/testsuite/g++.dg/cpp1z/pr99833.C
new file mode 100644
index 00000000000..f7c995887f8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/pr99833.C
@@ -0,0 +1,11 @@
+// PR c++/99833
+// { dg-do compile { target c++17 } }
+
+struct S { int a, b; };
+template <class>
+void
+foo ()
+{
+  [](auto d) { if constexpr (auto [a, b]{d}; sizeof (a) > 0) a++; } (S{});
+}
+template void foo<S> ();