On Fri, 16 Dec 2022, Jason Merrill wrote:
> On 12/16/22 11:45, Patrick Palka wrote:
> > Here we're rejecting the use of the captured 't' (of empty type) as a
> > template argument ultimately because convert_nontype_argument checks
> > potentiality using is_constant_expression which returns false for
> > captured variables since want_rval=false. But in this case an
> > lvalue-to-rvalue conversion of the argument is implied, so I believe we
> > should be checking is_rvalue_constant_expression.
> >
> > This patch defines an rvalue version of is_nondep_const_expr and uses
> > it in convert_nontype_argument when the target type is a non-reference.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look right?
> > Alternatively, since 'non_dep' in convert_nontype_argument controls only
> > whether we should call instantiate_non_dependent_expr, it seems weird to
> > me that we care about potentiality at all. So I experimented with using
> > instantiation_dependent_expression_p here instead, and that seemed to
> > work well and even fixed the dg-ice'd test cpp1z/constexpr-lambda26.C.
> > In r12-7564-gec0f53a3a542e7 we made a similar change to decltype.
>
> This approach sounds good to me.
Like so? Bootstrapped and regtested on x86_64-pc-linux-gnu.
-- >8 --
Subject: [PATCH] c++: constantness of non-dependent NTTP argument [PR107437]
Here we're rejecting the use of the captured 't' (of empty type) as a
template argument ultimately because convert_nontype_argument checks
constantness using is_constant_expression which returns false for
captured variables since want_rval=false. But in this case an
lvalue-to-rvalue conversion of the argument is implied, so I believe we
should be using is_rvalue_constant_expression instead.
However, it doesn't seem necessary to consider constantness at all
in convert_nontype_argument when determining whether to instantiate
a non-dependent argument. So this patch gets rid of the problematic
constantness test altogether, which is sufficient to fix the testcase
(as well as the similar dg-ice'd testcase from PR87765). Note that in
r12-7564-gec0f53a3a542e7 we made a similar change to finish_decltype_type.
PR c++/107437
PR c++/87765
gcc/cp/ChangeLog:
* pt.cc (convert_nontype_argument): Relax is_nondep_const_expr
test to !inst_dep_expr_p.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/lambda-generic-107437.C: New test.
* g++.dg/cpp1z/constexpr-lambda26.C: Remove dg-ice.
---
gcc/cp/pt.cc | 2 +-
.../g++.dg/cpp1y/lambda-generic-107437.C | 21 +++++++++++++++++++
.../g++.dg/cpp1z/constexpr-lambda26.C | 1 -
3 files changed, 22 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/lambda-generic-107437.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index bc566ab702b..2516cca590e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -7318,7 +7318,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
&& has_value_dependent_address (expr))
/* If we want the address and it's value-dependent, don't fold. */;
else if (processing_template_decl
- && is_nondependent_constant_expression (expr))
+ && !instantiation_dependent_expression_p (expr))
non_dep = true;
if (error_operand_p (expr))
return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-107437.C
b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-107437.C
new file mode 100644
index 00000000000..f9b4e0187e2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-107437.C
@@ -0,0 +1,21 @@
+// PR c++/107437
+// { dg-do compile { target c++14 } }
+
+struct integral_constant {
+ constexpr operator int() const { return 42; }
+};
+
+template<int N>
+struct A {
+ static constexpr int value = N;
+};
+
+template<class T>
+void f(T t) {
+ [=](auto) {
+ A<t> a; // { dg-bogus "constant" }
+ return a.value;
+ }(0);
+}
+
+template void f(integral_constant);
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda26.C
b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda26.C
index 0cdb400d21c..e66cd1dee64 100644
--- a/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda26.C
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-lambda26.C
@@ -1,7 +1,6 @@
// PR c++/87765
// { dg-do compile { target c++17 } }
// { dg-additional-options "-fchecking" }
-// { dg-ice "cxx_eval_constant_expression" }
template <int N>
using foo = int;
--
2.39.0.56.g57e2c6ebbe
