c++: spec_hasher::equal and PARM_DECLs [PR94632]

In the testcase below, during specialization of c<int>::d, we build two
identical specializations of the parameter type b<decltype(e)::k> -- one when
substituting into c<int>::d's TYPE_ARG_TYPES and another when substituting into
c<int>::d's DECL_ARGUMENTS.

We don't reuse the first specialization the second time around as a consequence
of the fix for PR c++/56247 which made PARM_DECLs always compare different from
one another during spec_hasher::equal.  As a result, when looking up existing
specializations of 'b', spec_hasher::equal considers the template argument
decltype(e')::k to be different from decltype(e'')::k, where e' and e'' are the
result of two calls to tsubst_copy on the PARM_DECL e.

Since the two specializations are considered different due to the mentioned fix,
their TYPE_CANONICAL points to themselves even though they are otherwise
identical types, and this triggers an ICE in maybe_rebuild_function_decl_type
when comparing the TYPE_ARG_TYPES of c<int>::d to its DECL_ARGUMENTS.

This patch fixes this issue at the spec_hasher::equal level by ignoring the
'comparing_specializations' flag in cp_tree_equal whenever the DECL_CONTEXTs of
the two parameters are identical.  This seems to be a sufficient condition to be
able to correctly compare PARM_DECLs structurally.  (This also subsumes the
CONSTRAINT_VAR_P check since constraint variables all have empty, and therefore
identical, DECL_CONTEXTs.)

gcc/cp/ChangeLog:

	PR c++/94632
	* tree.c (cp_tree_equal) <case PARM_DECL>: Ignore
	comparing_specializations if the parameters' contexts are identical.

gcc/testsuite/ChangeLog:

	PR c++/94632
	* g++.dg/template/canon-type-14.C: New test.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 45c422f59507e167ea2534a744b3ad0b805dae9d..9533cca713702cc3213e3ec4544343b23f117c02 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 2020-04-18  Patrick Palka  <ppalka@redhat.com>
 
+       PR c++/94632
+       * tree.c (cp_tree_equal) <case PARM_DECL>: Ignore
+       comparing_specializations if the parameters' contexts are identical.
+
        PR c++/92187
        * pt.c (splice_late_return_type): Propagate cv-qualifiers and
        PLACEHOLDER_TYPE_CONSTRAINTS from the original auto node to the new one.

diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 8e4934c00093ec5f5627b52049394cbbca17d81f..dc4f1f48d3c5cd6eae4f9bc5207d72286c517ab4 100644 (file)
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -3723,11 +3723,12 @@ cp_tree_equal (tree t1, tree t2)
         up for expressions that involve 'this' in a member function
         template.  */
 
-      if (comparing_specializations && !CONSTRAINT_VAR_P (t1))
+      if (comparing_specializations
+         && DECL_CONTEXT (t1) != DECL_CONTEXT (t2))
        /* When comparing hash table entries, only an exact match is
           good enough; we don't want to replace 'this' with the
           version from another function.  But be more flexible
-          with local parameters in a requires-expression.  */
+          with parameters with identical contexts.  */
        return false;
 
       if (same_type_p (TREE_TYPE (t1), TREE_TYPE (t2)))

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 08bef53e9112e5d1d960cd9be60eafafc41e494a..a41cc03f6fa2b1761618c62c9a8b9995737d5cac 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2020-04-18  Patrick Palka  <ppalka@redhat.com>
 
+       PR c++/94632
+       * g++.dg/template/canon-type-14.C: New test.
+
        PR c++/92187
        * g++.dg/concepts/abbrev5.C: New test.
        * g++.dg/concepts/abbrev6.C: New test.

diff --git a/gcc/testsuite/g++.dg/template/canon-type-14.C b/gcc/testsuite/g++.dg/template/canon-type-14.C
new file mode 100644 (file)
index 0000000..fa05bdb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/canon-type-14.C
@@ -0,0 +1,8 @@
+// PR c++/94632
+// { dg-do compile { target c++11 } }
+
+template <bool> struct b;
+template <typename> class c {
+  template <typename f> static void d(f e, b<decltype(e)::k>);
+};
+template class c<int>;