[PATCH] c++: bound ttp level lowering [PR109531]

[Patrick Palka <ppalka@redhat.com>]

Here when level lowering the bound ttp TT<typename T::type> via the
substitution T=C, we're neglecting to canonicalize (and therefore strip
of simple typedefs) the resulting template arguments {A<int>} before
determining its new canonical type via hash table lookup.  This leads to
an a hash mismatch ICE for the two equivalent types TT<int> and TT<A<int>>
since iterative_hash_template_arg misbehaves for a non-canonicalized type
argument.

We can fix this by canonicalizing or coercing the substituted arguments
directly, but given that creation and ordinary substitution of bound
ttps both go through lookup_template_class, which in turn performs
coercion/canonicalization, it seems best to make this code path go
through lookup_template_class as well.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/13?

	PR c++/109531

gcc/cp/ChangeLog:

	* pt.cc (tsubst) <case BOUND_TEMPLATE_TEMPLATE_PARM>:
	In the level-lowering case just use lookup_template_class
	to rebuild the bound ttp.

gcc/testsuite/ChangeLog:

	* g++.dg/template/canon-type-20.C: New test.
	* g++.dg/template/ttp36.C: New test.
---
 gcc/cp/pt.cc                                  | 39 ++++++++++---------
 gcc/testsuite/g++.dg/template/canon-type-20.C | 18 +++++++++
 gcc/testsuite/g++.dg/template/ttp36.C         | 12 ++++++
 3 files changed, 50 insertions(+), 19 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/template/canon-type-20.C
 create mode 100644 gcc/testsuite/g++.dg/template/ttp36.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fcc8e0d1d57..e065ace5c55 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -16232,7 +16232,6 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	  {
 	  case TEMPLATE_TYPE_PARM:
 	  case TEMPLATE_TEMPLATE_PARM:
-	  case BOUND_TEMPLATE_TEMPLATE_PARM:
 	    if (cp_type_quals (t))
 	      {
 		r = tsubst (TYPE_MAIN_VARIANT (t), args, complain, in_decl);
@@ -16274,24 +16273,6 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 		       only instantiated during satisfaction.  */
 		    PLACEHOLDER_TYPE_CONSTRAINTS_INFO (r) = ci;
 
-		if (code == BOUND_TEMPLATE_TEMPLATE_PARM)
-		  {
-		    tree tinfo = TYPE_TEMPLATE_INFO (t);
-		    /* We might need to substitute into the types of non-type
-		       template parameters.  */
-		    tree tmpl = tsubst (TI_TEMPLATE (tinfo), args,
-					complain, in_decl);
-		    if (tmpl == error_mark_node)
-		      return error_mark_node;
-		    tree argvec = tsubst (TI_ARGS (tinfo), args,
-					  complain, in_decl);
-		    if (argvec == error_mark_node)
-		      return error_mark_node;
-
-		    TEMPLATE_TEMPLATE_PARM_TEMPLATE_INFO (r)
-		      = build_template_info (tmpl, argvec);
-		  }
-
 		if (TYPE_STRUCTURAL_EQUALITY_P (t))
 		  SET_TYPE_STRUCTURAL_EQUALITY (r);
 		else
@@ -16299,6 +16280,26 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	      }
 	    break;
 
+	  case BOUND_TEMPLATE_TEMPLATE_PARM:
+	    {
+	      tree tinfo = TYPE_TEMPLATE_INFO (t);
+	      /* We might need to substitute into the types of non-type
+		 template parameters.  This also lowers the level of
+		 the ttp appropriately.  */
+	      tree tmpl = tsubst (TI_TEMPLATE (tinfo), args,
+				  complain, in_decl);
+	      if (tmpl == error_mark_node)
+		return error_mark_node;
+	      tree argvec = tsubst (TI_ARGS (tinfo), args,
+				    complain, in_decl);
+	      if (argvec == error_mark_node)
+		return error_mark_node;
+	      r = lookup_template_class (tmpl, argvec, in_decl, NULL_TREE,
+					 /*entering_scope=*/false, complain);
+	      r = cp_build_qualified_type (r, cp_type_quals (t), complain);
+	      break;
+	    }
+
 	  case TEMPLATE_PARM_INDEX:
 	    /* OK, now substitute the type of the non-type parameter.  We
 	       couldn't do it earlier because it might be an auto parameter,
diff --git a/gcc/testsuite/g++.dg/template/canon-type-20.C b/gcc/testsuite/g++.dg/template/canon-type-20.C
new file mode 100644
index 00000000000..e40261037e5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/canon-type-20.C
@@ -0,0 +1,18 @@
+// PR c++/109531
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "--param=hash-table-verification-limit=1000" }
+
+template<class T>
+using A = int;
+
+struct B { using type = int; };
+struct C { using type = A<int>; };
+
+template<class T>
+struct D {
+  template<template<class> class TT>
+  TT<typename T::type> f ();
+};
+
+template struct D<B>;
+template struct D<C>;
diff --git a/gcc/testsuite/g++.dg/template/ttp36.C b/gcc/testsuite/g++.dg/template/ttp36.C
new file mode 100644
index 00000000000..2df00855cf7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp36.C
@@ -0,0 +1,12 @@
+// Verify we propagate cv-quals when level-lowering a bound ttp.
+
+template<class T>
+struct B {
+  template<template<class> class TT>
+  void f(const TT<T> *);
+
+  template<template<class> class TT>
+  void f(TT<T> *); // { dg-bogus "cannot be overloaded" }
+};
+
+template struct B<int>;
-- 
2.40.0.335.g9857273be0