[COMMITTED 2/2] c++: Fix constexpr vs. reference parameter.
Jason Merrill
jason@redhat.com
Mon Feb 3 22:52:00 GMT 2020
[expr.const] specifically rules out mentioning a reference even if its
address is never used, because it implies indirection that is similarly
non-constant for a pointer variable.
Tested x86_64-pc-linux-gnu, applying to trunk.
PR c++/66477
* constexpr.c (cxx_eval_constant_expression) [PARM_DECL]: Don't
defer loading the value of a reference.
---
gcc/cp/constexpr.c | 2 -
.../g++.dg/cpp0x/constexpr-array-ptr6.C | 2 +-
gcc/testsuite/g++.dg/cpp0x/constexpr-ref12.C | 46 +++++++++++++++++++
.../g++.dg/cpp1y/lambda-generic-const10.C | 2 +-
4 files changed, 48 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-ref12.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index a39ba413d68..3962763fb21 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -5322,8 +5322,6 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
r = *p;
else if (lval)
/* Defer in case this is only used for its type. */;
- else if (TYPE_REF_P (TREE_TYPE (t)))
- /* Defer, there's no lvalue->rvalue conversion. */;
else if (COMPLETE_TYPE_P (TREE_TYPE (t))
&& is_really_empty_class (TREE_TYPE (t), /*ignore_vptr*/false))
{
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array-ptr6.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array-ptr6.C
index 3a483989c1f..1c065120314 100644
--- a/gcc/testsuite/g++.dg/cpp0x/constexpr-array-ptr6.C
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array-ptr6.C
@@ -12,7 +12,7 @@ constexpr auto sz_d = size(array_double);
static_assert(sz_d == 3, "Array size failure");
void f(bool (¶m)[2]) {
- static_assert(size(param) == 2, "Array size failure"); // Line 13
+ static_assert(size(param) == 2, "Array size failure"); // { dg-error "" }
short data[] = {-1, 2, -45, 6, 88, 99, -345};
static_assert(size(data) == 7, "Array size failure");
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ref12.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-ref12.C
new file mode 100644
index 00000000000..7c3ce66b4c9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ref12.C
@@ -0,0 +1,46 @@
+// PR c++/66477
+// { dg-do compile { target c++11 } }
+
+struct a { constexpr bool g() const { return true; } };
+constexpr bool g(a&) { return true;}
+constexpr bool h(a) { return true;}
+
+a a1;
+a& ar = a1;
+
+void f(a ap, a& arp)
+{
+ a a2;
+ a& ar2 = a2;
+
+ // Most of these are OK because no data is actually loaded.
+ static_assert (a1.g(),"");
+ static_assert (g(a1),"");
+ static_assert (h(a1),"");
+
+ static_assert (a2.g(),"");
+ static_assert (g(a2),"");
+ static_assert (h(a2),"");
+
+ static_assert (ap.g(),"");
+ static_assert (g(ap),"");
+ static_assert (h(ap),"");
+
+ static_assert (ar.g(),"");
+ static_assert (g(ar),"");
+ static_assert (h(ar),"");
+
+ // But these are specifically prohibited in [expr.const]/4.12:
+ // * an id-expression that refers to a variable or data member of reference
+ // type unless the reference has a preceding initialization and either
+ // ** it is usable in constant expressions or
+ // ** its lifetime began within the evaluation of e;
+
+ static_assert (ar2.g(),""); // { dg-error "constant" }
+ static_assert (g(ar2),""); // { dg-error "constant" }
+ static_assert (h(ar2),""); // { dg-error "constant" }
+
+ static_assert (arp.g(),""); // { dg-error "constant" }
+ static_assert (g(arp),""); // { dg-error "constant" }
+ static_assert (h(arp),""); // { dg-error "constant" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const10.C b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const10.C
index e0080b3d4f6..2f48dae4746 100644
--- a/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const10.C
+++ b/gcc/testsuite/g++.dg/cpp1y/lambda-generic-const10.C
@@ -11,7 +11,7 @@ int main()
constexpr auto x = f(); //ok, call constexpr const non-static method
[](auto const &f) {
- constexpr auto x = f(); /*ok*/
+ constexpr auto x = f(); // { dg-error "" }
}(f);
[&]() {
--
2.18.1
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