On 1/31/24 16:03, Patrick Palka wrote:
On Wed, 31 Jan 2024, Jason Merrill wrote:
On 1/31/24 12:12, Patrick Palka wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
-- >8 --
Here during declaration matching we undesirably consider the two TT{42}
CTAD expressions to be non-equivalent ultimately because for CTAD
placeholder equivalence we compare the TEMPLATE_DECLs (which uses
pointer identity) and here the corresponding TEMPLATE_DECLs for TT are
different since they're from different scopes. On the other hand, the
corresponding TEMPLATE_TEMPLATE_PARMs are deemed equivalent (since they
have the same position and template parameters). This turns out to be
the root cause of some of the xtreme-header modules regressions.
We don't have this ttp equivalence issue in other contexts because either
the TEMPLATE_TEMPLATE_PARM is used instead of the TEMPLATE_DECL already
(e.g. when a ttp is used as a targ), or the equivalence logic is relaxed
(e.g. for bound ttps), it seems.
So this patch relaxes ttp CTAD placeholder equivalence accordingly, by
comparing the TEMPLATE_TEMPLATE_PARM instead of the TEMPLATE_DECL. The
ctp_hasher doesn't need to be adjusted since it currently doesn't include
CLASS_PLACEHOLDER_TEMPLATE in the hash anyway.
Maybe put this handling in cp_tree_equal and call it from here? Does
iterative_hash_template_arg need something similar?
I was hoping cp_tree_equal would never be called for a ttp TEMPLATE_DECL
after this patch, and so it wouldn't matter either way, but it turns out
to matter for a function template-id:
template<template<class> class, class T>
void g(T);
template<template<class> class TT, class T>
decltype(g<TT>(T{})) f(T); // #1
template<template<class> class TT, class T>
decltype(g<TT>(T{})) f(T); // redeclaration of #1
template<class T> struct A { A(T); };
int main() {
f<A>(0);
}
Here we represent TT in g<TT> as a TEMPLATE_DECL because it's not until
coercion that convert_template_argument turns it into a
TEMPLATE_TEMPLATE_PARM, but of course we can't coerce until the call is
non-dependent and we know which function we're calling. (So TT within
a class, variable or alias template-id would be represented as a
TEMPLATE_TEMPLATE_PARM since we can do coercion ahead of time in that
case.)
So indeed it seems desirable to handle this in cp_tree_equal... like so?
Bootstrap and regtest nearly finished.
OK.
-- >8 --
PR c++/112737
gcc/cp/ChangeLog:
* pt.cc (iterative_hash_template_arg) <case TEMPLATE_DECL>:
Adjust hashing to match cp_tree_equal.
(ctp_hasher::hash): Also hash CLASS_PLACEHOLDER_TEMPLATE.
* tree.cc (cp_tree_equal) <case TEMPLATE_DECL>: Return true
for ttp TEMPLATE_DECLs if their TEMPLATE_TEMPLATE_PARMs are
equivalent.
* typeck.cc (structural_comptypes) <case TEMPLATE_TYPE_PARM>:
Use cp_tree_equal to compare CLASS_PLACEHOLDER_TEMPLATE.
gcc/testsuite/ChangeLog:
* g++.dg/template/ttp42.C: New test.
* g++.dg/template/ttp42a.C: New test.
---
gcc/cp/pt.cc | 9 +++++++++
gcc/cp/tree.cc | 6 +++++-
gcc/cp/typeck.cc | 4 ++--
gcc/testsuite/g++.dg/template/ttp42.C | 14 ++++++++++++++
gcc/testsuite/g++.dg/template/ttp42a.C | 18 ++++++++++++++++++
5 files changed, 48 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/template/ttp42.C
create mode 100644 gcc/testsuite/g++.dg/template/ttp42a.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 5871cb668d0..ca454758ca7 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -1816,6 +1816,13 @@ iterative_hash_template_arg (tree arg, hashval_t val)
}
return iterative_hash_template_arg (TREE_TYPE (arg), val);
+ case TEMPLATE_DECL:
+ if (DECL_TEMPLATE_TEMPLATE_PARM_P (arg))
+ return iterative_hash_template_arg (TREE_TYPE (arg), val);
+ else
+ /* Hash it like any other declaration. */
+ break;
+
case TARGET_EXPR:
return iterative_hash_template_arg (TARGET_EXPR_INITIAL (arg), val);
@@ -4499,6 +4506,8 @@ struct ctp_hasher : ggc_ptr_hash<tree_node>
hashval_t val = iterative_hash_object (code, 0);
val = iterative_hash_object (TEMPLATE_TYPE_LEVEL (t), val);
val = iterative_hash_object (TEMPLATE_TYPE_IDX (t), val);
+ if (TREE_CODE (t) == TEMPLATE_TYPE_PARM)
+ val = iterative_hash_template_arg (CLASS_PLACEHOLDER_TEMPLATE (t), val);
if (TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM)
val = iterative_hash_template_arg (TYPE_TI_ARGS (t), val);
--comparing_specializations;
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 77f57e0f9ac..5c8c05dc168 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -4084,11 +4084,15 @@ cp_tree_equal (tree t1, tree t2)
}
return false;
+ case TEMPLATE_DECL:
+ if (DECL_TEMPLATE_TEMPLATE_PARM_P (t1)
+ && DECL_TEMPLATE_TEMPLATE_PARM_P (t2))
+ return cp_tree_equal (TREE_TYPE (t1), TREE_TYPE (t2));
+ /* Fall through. */
case VAR_DECL:
case CONST_DECL:
case FIELD_DECL:
case FUNCTION_DECL:
- case TEMPLATE_DECL:
case IDENTIFIER_NODE:
case SSA_NAME:
case USING_DECL:
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index a15eda3f5f8..87109e63138 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -1573,8 +1573,8 @@ structural_comptypes (tree t1, tree t2, int strict)
return false;
/* If T1 and T2 don't represent the same class template deduction,
they aren't equal. */
- if (CLASS_PLACEHOLDER_TEMPLATE (t1)
- != CLASS_PLACEHOLDER_TEMPLATE (t2))
+ if (!cp_tree_equal (CLASS_PLACEHOLDER_TEMPLATE (t1),
+ CLASS_PLACEHOLDER_TEMPLATE (t2)))
return false;
/* Constrained 'auto's are distinct from parms that don't have the same
constraints. */
diff --git a/gcc/testsuite/g++.dg/template/ttp42.C
b/gcc/testsuite/g++.dg/template/ttp42.C
new file mode 100644
index 00000000000..da08e857fc5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp42.C
@@ -0,0 +1,14 @@
+// PR c++/112737
+// { dg-do compile { target c++17 } }
+
+template<template<class> class TT>
+decltype(TT{42}) f(); // #1
+
+template<template<class> class TT>
+decltype(TT{42}) f(); // redeclaration of #1
+
+template<class T> struct A { A(T); };
+
+int main() {
+ f<A>();
+}
diff --git a/gcc/testsuite/g++.dg/template/ttp42a.C
b/gcc/testsuite/g++.dg/template/ttp42a.C
new file mode 100644
index 00000000000..e890deda3a3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp42a.C
@@ -0,0 +1,18 @@
+// PR c++/112737
+// A version of ttp42.C using a function template-id instead of ttp CTAD.
+// { dg-do compile { target c++11 } }
+
+template<template<class> class, class T>
+void g(T);
+
+template<template<class> class TT, class T>
+decltype(g<TT>(T{})) f(T); // #1
+
+template<template<class> class TT, class T>
+decltype(g<TT>(T{})) f(T); // redeclaration of #1
+
+template<class T> struct A { A(T); };
+
+int main() {
+ f<A>(0);
+}
