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* [gcc r13-2633] c++: template-id arguments are evaluated [PR101906]
@ 2022-09-12 21:06 Patrick Palka
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From: Patrick Palka @ 2022-09-12 21:06 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:c3ba0eaaa223f7b8208d279e3f39ff134912f9e9
commit r13-2633-gc3ba0eaaa223f7b8208d279e3f39ff134912f9e9
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Jun 7 14:19:53 2022 -0400
c++: template-id arguments are evaluated [PR101906]
Here we're neglecting to clear cp_unevaluated_operand when substituting
into the arguments of the alias template-id 'skip<(T(), 0), T>' with T=A,
which means cp_unevaluated_operand remains set during mark_used for
A::A() and so we don't synthesize it. Later constant evaluation for
the substituted template argument '(A(), 0)' (from coerce_template_parms)
fails with "'constexpr A::A()' used before its definition" since it was
never synthesized.
This doesn't happen with a class template because tsubst_aggr_type
clears cp_unevaluated_operand during substitution thereof. But since
template arguments are generally manifestly constant-evaluated, which in
turn are evaluated even in an unevaluated operand, we should be clearing
cp_unevaluated_operand more broadly whenever substituting into any set
of template arguments. To that end this patch makes us clear it during
tsubst_template_args.
PR c++/101906
gcc/cp/ChangeLog:
* pt.cc (tsubst_template_args): Set cp_evaluated here.
(tsubst_aggr_type): Not here.
gcc/testsuite/ChangeLog:
* g++.dg/template/evaluated1.C: New test.
* g++.dg/template/evaluated1a.C: New test.
* g++.dg/template/evaluated1b.C: New test.
* g++.dg/template/evaluated1c.C: New test.
Diff:
---
gcc/cp/pt.cc | 6 +++---
gcc/testsuite/g++.dg/template/evaluated1.C | 17 +++++++++++++++++
gcc/testsuite/g++.dg/template/evaluated1a.C | 16 ++++++++++++++++
gcc/testsuite/g++.dg/template/evaluated1b.C | 17 +++++++++++++++++
gcc/testsuite/g++.dg/template/evaluated1c.C | 17 +++++++++++++++++
5 files changed, 70 insertions(+), 3 deletions(-)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 31e3e391098..4c6b343ab6e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -13616,6 +13616,9 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl)
if (t == error_mark_node)
return error_mark_node;
+ /* In "sizeof(X<I>)" we need to evaluate "I". */
+ cp_evaluated ev;
+
const int len = TREE_VEC_LENGTH (t);
tree *elts = XALLOCAVEC (tree, len);
int expanded_len_adjust = 0;
@@ -13888,9 +13891,6 @@ tsubst_aggr_type (tree t,
tree argvec;
tree r;
- /* In "sizeof(X<I>)" we need to evaluate "I". */
- cp_evaluated ev;
-
/* Figure out what arguments are appropriate for the
type we are trying to find. For example, given:
diff --git a/gcc/testsuite/g++.dg/template/evaluated1.C b/gcc/testsuite/g++.dg/template/evaluated1.C
new file mode 100644
index 00000000000..41845c65acb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/evaluated1.C
@@ -0,0 +1,17 @@
+// PR c++/101906
+// Verify the template arguments of an alias template-id are evaluated even
+// in an unevaluated context.
+// { dg-do compile { target c++11 } }
+
+template<int, class T> using skip = T;
+
+template<class T>
+constexpr unsigned sizeof_() {
+ return sizeof(skip<(T(), 0), T>);
+}
+
+struct A {
+ int m = -1;
+};
+
+static_assert(sizeof_<A>() == sizeof(A), "");
diff --git a/gcc/testsuite/g++.dg/template/evaluated1a.C b/gcc/testsuite/g++.dg/template/evaluated1a.C
new file mode 100644
index 00000000000..78286871004
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/evaluated1a.C
@@ -0,0 +1,16 @@
+// PR c++/101906
+// Like unevaluated1.C, but where the unevaluated context is a
+// constraint instead of sizeof.
+// { dg-do compile { target c++20 } }
+
+template<int> using voidify = void;
+
+template<class T>
+concept constant_value_initializable
+ = requires { typename voidify<(T(), 0)>; };
+
+struct A {
+ int m = -1;
+};
+
+static_assert(constant_value_initializable<A>);
diff --git a/gcc/testsuite/g++.dg/template/evaluated1b.C b/gcc/testsuite/g++.dg/template/evaluated1b.C
new file mode 100644
index 00000000000..7994065ac86
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/evaluated1b.C
@@ -0,0 +1,17 @@
+// PR c++/101906
+// Like unevaluated1.C, but using a function template instead of an
+// alias template.
+// { dg-do compile { target c++14 } }
+
+template<int, class T> T skip();
+
+template<class T>
+constexpr unsigned sizeof_() {
+ return sizeof(skip<(T(), 0), T>());
+}
+
+struct A {
+ int m = -1;
+};
+
+static_assert(sizeof_<A>() == sizeof(A), "");
diff --git a/gcc/testsuite/g++.dg/template/evaluated1c.C b/gcc/testsuite/g++.dg/template/evaluated1c.C
new file mode 100644
index 00000000000..15c55821c01
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/evaluated1c.C
@@ -0,0 +1,17 @@
+// PR c++/101906
+// Like unevaluated1b.C, but using a variable template instead of a
+// function template.
+// { dg-do compile { target c++14 } }
+
+template<int, class T> T skip;
+
+template<class T>
+constexpr unsigned sizeof_() {
+ return sizeof(skip<(T(), 0), T>);
+}
+
+struct A {
+ int m = -1;
+};
+
+static_assert(sizeof_<A>() == sizeof(A), "");
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