On 6/1/22 12:44, Patrick Palka wrote:
As explained in r11-4959-gde6f64f9556ae3, the atom cache assumes two
equivalent expressions (according to cp_tree_equal) must use the same
template parameters (according to find_template_parameters). This
assumption turned out to not hold for TARGET_EXPR, which was addressed
by that commit.
But this assumption apparently doesn't hold for PARM_DECL either:
find_template_parameters walks its DECL_CONTEXT but cp_tree_equal by
default doesn't consider DECL_CONTEXT unless comparing_specializations
is set. Thus in the first testcase below, the atomic constraints of #1
and #2 are equivalent according to cp_tree_equal, but according to
find_template_parameters the former uses T and the latter uses both T
and U.
I suppose we can fix this assumption violation by setting
comparing_specializations in the atom_hasher, which would make
cp_tree_equal return false for the two atoms, but that seems overly
pessimistic here. Ideally the atoms should be considered equivalent
and we should fix find_template_paremeters to return just T for #2's
atom.
To that end this patch makes for_each_template_parm_r stop walking the
DECL_CONTEXT of a PARM_DECL. This should be safe to do because
tsubst_copy / tsubst_decl only cares about the TREE_TYPE of a PARM_DECL
and doesn't bother substituting the DECL_CONTEXT, thus the only relevant
template parameters are those used in its type. any_template_parm_r is
currently responsible for walking its TREE_TYPE, but I suppose it now makes
sense make for_each_template_parm_r do so instead.
In passing this patch also makes for_each_template_parm_r stop walking
the DECL_CONTEXT of a VAR_/FUNCTION_DECL since it should be unnecessary
after walking DECL_TI_ARGS.
I experimented with not walking DECL_CONTEXT for CONST_DECL, but the
second testcase below demonstrates it's necessary to walk it.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
OK.
PR c++/105797
gcc/cp/ChangeLog:
* pt.cc (for_each_template_parm_r) <case FUNCTION_DECL, VAR_DECL>:
Don't walk DECL_CONTEXT.
<case PARM_DECL>: Likewise. Walk TREE_TYPE.
<case CONST_DECL>: Simplify accordingly.
(any_template_parm_r) <case PARM_DECL>: Don't walk TREE_TYPE.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-decltype4.C: New test.
---
gcc/cp/pt.cc | 10 +++++-----
gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C | 16 ++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C | 12 ++++++++++++
3 files changed, 33 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4f0ace2644b..e4a473002a0 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -10561,11 +10561,14 @@ for_each_template_parm_r (tree *tp, int
*walk_subtrees, void *d)
case VAR_DECL:
if (DECL_LANG_SPECIFIC (t) && DECL_TEMPLATE_INFO (t))
WALK_SUBTREE (DECL_TI_ARGS (t));
- /* Fall through. */
+ break;
case PARM_DECL:
+ WALK_SUBTREE (TREE_TYPE (t));
+ break;
+
case CONST_DECL:
- if (TREE_CODE (t) == CONST_DECL && DECL_TEMPLATE_PARM_P (t))
+ if (DECL_TEMPLATE_PARM_P (t))
WALK_SUBTREE (DECL_INITIAL (t));
if (DECL_CONTEXT (t)
&& pfd->include_nondeduced_p)
@@ -10824,9 +10827,6 @@ any_template_parm_r (tree t, void *data)
break;
case TEMPLATE_PARM_INDEX:
- case PARM_DECL:
- /* A parameter or constraint variable may also depend on a template
- parameter without explicitly naming it. */
WALK_SUBTREE (TREE_TYPE (t));
break;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C
new file mode 100644
index 00000000000..6683d224cf8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-decltype4.C
@@ -0,0 +1,16 @@
+// PR c++/105797
+// { dg-do compile { target c++20 } }
+
+template<class T>
+concept C = requires { T(); };
+
+template<class T>
+void f(T v) requires C<decltype(v)>; // #1
+
+template<class T, class U>
+void f(T v) requires C<decltype(v)>; // #2
+
+int main() {
+ f<int, int>(0);
+ f<int>(0);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C
new file mode 100644
index 00000000000..3fa4fb82818
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun3.C
@@ -0,0 +1,12 @@
+// { dg-do compile { target c++20 } }
+
+template<class T, int I>
+struct A {
+ enum E { e = I };
+ static void f() requires (e != 0);
+};
+
+int main() {
+ A<int, 1>::f();
+ A<int, 0>::f(); // { dg-error "no match" }
+}
