Patchwork C++ PATCH for c++/53498 (infinite tsubst recursion with variadic template)

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Submitter Jason Merrill
Date June 26, 2012, 3:39 a.m.
Message ID <4FE92F07.8020508@redhat.com>
Download mbox | patch
Permalink /patch/167312/
State New
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Comments

Jason Merrill - June 26, 2012, 3:39 a.m.
Here, the problem was that when we substitute into a parameter pack 
PARM_DECL to get a dummy decl for use in a decltype context, we were 
continuing to tsubst into its DECL_CHAIN as well, which causes problems 
if a following parameter uses the previous parameter, as in this testcase.

In tsubst_copy we've dealt with this issue for non-pack parameters by 
doing a copy_node before calling tsubst_decl, but it occurred to me that 
we could check cp_unevaluated_context instead to avoid the extra allocation.

Tested x86_64-pc-linux-gnu, applying to trunk.  Alternative patch that 
just does the copy for packs as well tested and applying to 4.7.

Patch

commit 1965f161a59d81a408cd2369e7a393fa17e95ede
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 25 17:32:32 2012 -0400

    	PR c++/53498
    	PR c++/53305
    	* pt.c (tsubst_pack_expansion): Copy before dummy tsubst.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 7f5682d..1b5ab9e 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -9393,7 +9393,9 @@  tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
 		 late-specified return type).  Even if it exists, it might
 		 have the wrong value for a recursive call.  Just make a
 		 dummy decl, since it's only used for its type.  */
-	      arg_pack = tsubst_decl (parm_pack, args, complain);
+	      /* Copy before tsubsting so that we don't recurse into any
+		 later PARM_DECLs.  */
+	      arg_pack = tsubst_decl (copy_node (parm_pack), args, complain);
 	      if (arg_pack && FUNCTION_PARAMETER_PACK_P (arg_pack))
 		/* Partial instantiation of the parm_pack, we can't build
 		   up an argument pack yet.  */
diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype38.C b/gcc/testsuite/g++.dg/cpp0x/decltype38.C
new file mode 100644
index 0000000..97ebb33
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/decltype38.C
@@ -0,0 +1,17 @@ 
+// PR c++/53498
+// { dg-do compile { target c++11 } }
+
+template<typename... Args>
+struct B
+{
+  template<typename U>
+  static
+  void b(const U& u, const Args&... args,
+	 decltype(u.f(args...)) dummy)
+  {
+  }
+};
+
+int main() {
+  B<int> b;
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic132.C b/gcc/testsuite/g++.dg/cpp0x/variadic132.C
new file mode 100644
index 0000000..1b9c286
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic132.C
@@ -0,0 +1,27 @@ 
+// PR c++/53305
+// { dg-do compile { target c++11 } }
+
+template<class... Ts> struct tuple { };
+
+struct funct
+{
+  template<class... argTs>
+  int operator()(argTs...);
+};
+
+template<class...> struct test;
+
+template<template <class...> class tp,
+	 class... arg1Ts, class... arg2Ts>
+struct test<tp<arg1Ts...>, tp<arg2Ts...>>
+{
+  template<class func, class...arg3Ts>
+    auto test2(func fun, arg1Ts... arg1s, arg3Ts... arg3s)
+    -> decltype(fun(arg1s..., arg3s...));
+};
+
+int main()
+{
+  test<tuple<>, tuple<char,int>> t2;
+  t2.test2(funct(), 'a', 2);
+}