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 --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index a0ca65cfa0de45127b289f436b4e72d7951af2f1..19fdafa4c43c8232bedd5beb9a717c9bdb166a86 100644 (file)
--- 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 (file)
index 0000000..f7c9958
--- /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 (file)
index 0000000..3323053
--- /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);
+}