[gcc r11-8209] c++: Fix up handling of structured bindings in extract_locals_r [PR99833]

[gcc r11-8209] c++: Fix up handling of structured bindings in extract_locals_r [PR99833]

[Jakub Jelinek]

https://gcc.gnu.org/g:20eb7a1891cfd7fa85295a236cebe0322d041edd

commit r11-8209-g20eb7a1891cfd7fa85295a236cebe0322d041edd
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.
            * g++.dg/cpp2a/pr99833.C: New test.

Diff:
---
 gcc/cp/pt.c                          | 22 +++++++++++++++++++++-
 gcc/testsuite/g++.dg/cpp1z/pr99833.C | 11 +++++++++++
 gcc/testsuite/g++.dg/cpp2a/pr99833.C | 18 ++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index a0ca65cfa0d..19fdafa4c43 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12830,7 +12830,27 @@ 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_CODE (*tp) == LAMBDA_EXPR)
     {
       /* Since we defer implicit capture, look in the parms and body.  */
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> ();
diff --git a/gcc/testsuite/g++.dg/cpp2a/pr99833.C b/gcc/testsuite/g++.dg/cpp2a/pr99833.C
new file mode 100644
index 00000000000..33230535e10
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/pr99833.C
@@ -0,0 +1,18 @@
+// PR c++/99833
+// { dg-do compile { target c++20 } }
+
+#include <tuple>
+
+auto f(auto&& x)
+{
+  [&](auto...) {
+    auto y = std::tuple{ "what's happening here?", x };
+    if constexpr (auto [_, z] = y; requires { z; })
+      return;
+  }();
+}
+
+int main()
+{
+  f(42);
+}