On 7/7/20 3:36 PM, Patrick Palka wrote:
On Tue, 7 Jul 2020, Jason Merrill wrote:
On 7/7/20 9:33 AM, Patrick Palka wrote:
We are ICEing in the testcase below because we pass the
yet-uninstantiated class type A<int> of the PARM_DECL b to
is_really_empty_class from potential_rvalue_constant_expression when
parsing the requirement t += b.
Why are we getting to potential_rvalue_constant_expression? My guess is from
build_non_dependent_expr because processing_constraint isn't set?
My mistake, I meant to write that we are calling is_really_empty_class
from is_rvalue_constant_expression, not from
potential_rvalue_constant_expression. And we're getting to
is_rvalue_constant_expression from cp_parser_constant_expression when
parsing the RHS of the assignment.
Most of the parser constant-expression stuff is a relic of C++98; I
tried changing cp_parser_constant_expression to only check constancy
when we're requiring a constant expression, but that broke some library
tests for some reason.
This patch fixes the ICE by guarding the problematic call to
is_really_empty_class with a COMPLETE_TYPE_P check, which should also
subsume the existing dependent_type_p check.
OK.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK to
commit to trunk and to the 10 branch?
gcc/cp/ChangeLog:
PR c++/95497
* constexpr.c (potential_constant_expression_1): When
processing_template_decl, check COMPLETE_TYPE_P before calling
is_really_empty_class.
gcc/testsuite/ChangeLog:
PR c++/95497
* g++.dg/cpp2a/concepts-pr95497.C: New test.
---
gcc/cp/constexpr.c | 2 +-
gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C | 12 ++++++++++++
2 files changed, 13 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 1939166e907..ff78ebda2dc 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7443,7 +7443,7 @@ potential_constant_expression_1 (tree t, bool
want_rval, bool strict, bool now,
if (now && want_rval)
{
tree type = TREE_TYPE (t);
- if (dependent_type_p (type)
+ if ((processing_template_decl && !COMPLETE_TYPE_P (type))
|| is_really_empty_class (type, /*ignore_vptr*/false))
/* An empty class has no data to read. */
return true;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
new file mode 100644
index 00000000000..4d7718ad5e8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
@@ -0,0 +1,12 @@
+// PR c++/95497
+// { dg-do compile { target c++20 } }
+
+template <typename T>
+struct A{};
+
+template <typename T>
+concept c =
+ requires(T t, A<int> b) // note that A<int> is independent of T
+ {
+ { t += b };
+ };
