From a6ac1fc64c3caed19da65c2e6b12f8ddaf551231 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Mon, 18 Sep 2023 14:41:07 -0400
Subject: [PATCH] c++: unifying identical tmpls from current inst [PR108347]
Here more_specialized_partial_spec wrongly considers the two partial
specializations to be unordered ultimately because unify for identical
parm=arg=A<T>::C returns failure due to C being dependent.
This patch fixes this by relaxing unify's early-exit identity test to
also accept dependent decls; we can't deduce anything further from them
anyway. In passing this patch removes the CONST_DECL case of unify:
we should never see the CONST_DECL version of a template parameter here,
and for other CONST_DECLs (such as enumerators) it seems we can rely on
them to already have been folded to their DECL_INITIAL.
PR c++/108347
gcc/cp/ChangeLog:
* pt.cc (unify): Return unify_success for identical dependent
DECL_P 'arg' and 'parm'.
<case CONST_DECL>: Remove handling.
gcc/testsuite/ChangeLog:
* g++.dg/template/ttp41.C: New test.
---
gcc/cp/pt.cc | 10 ++++------
gcc/testsuite/g++.dg/template/ttp41.C | 17 +++++++++++++++++
2 files changed, 21 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/ttp41.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index a40b8953e629..31ff80ea6e74 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24559,7 +24559,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
even if ARG == PARM, since we won't record unifications for the
template parameters. We might need them if we're trying to
figure out which of two things is more specialized. */
- if (arg == parm && !uses_template_parms (parm))
+ if (arg == parm
+ && (DECL_P (parm) || !uses_template_parms (parm)))
return unify_success (explain_p);
/* Handle init lists early, so the rest of the function can assume
@@ -25278,11 +25279,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
strict, explain_p);
case CONST_DECL:
- if (DECL_TEMPLATE_PARM_P (parm))
- return unify (tparms, targs, DECL_INITIAL (parm), arg, strict, explain_p);
- if (arg != scalar_constant_value (parm))
- return unify_template_argument_mismatch (explain_p, parm, arg);
- return unify_success (explain_p);
+ /* CONST_DECL should already have been folded to its DECL_INITIAL. */
+ gcc_unreachable ();
case FIELD_DECL:
case TEMPLATE_DECL:
diff --git a/gcc/testsuite/g++.dg/template/ttp41.C b/gcc/testsuite/g++.dg/template/ttp41.C
new file mode 100644
index 000000000000..c81e5dd24054
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp41.C
@@ -0,0 +1,17 @@
+// PR c++/108347
+
+template<class T>
+struct A {
+ template<class U> struct C { };
+
+ template<template<class> class TT, class U>
+ struct B;
+
+ template<class U>
+ struct B<C, U*>;
+
+ template<class U>
+ struct B<C, const U*> { };
+};
+
+A<int>::B<A<int>::C, const int*> b;
--
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