This is a similar problem to 83116: we'd cached a constexpr call, but after a
store the result had become invalid, yet we used the wrong result again when
encountering the same call later. This resulted in evaluating a THROW_EXPR
which doesn't work. Details in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83692#c5
The fix for 83116 didn't work here, because when evaluating the body of the
ctor via store_init_value -> cxx_constant_value we are in STRICT, so we do
cache.
It seems that we may no longer rely on the constexpr call table when we
do cxx_eval_store_expression, because that just rewrites *valp, i.e. the
value of an object. Might be too big a hammer again, but I couldn't think
of how I could guard the caching of a constexpr call.
This doesn't manifest in C++14 because build_special_member_call in C++17 is
more aggressive with copy elisions (as required by P0135 which changed how we
view prvalues). In C++14 build_special_member_call produces a CALL_EXPR, so
expand_default_init calls maybe_constant_init, for which STRICT is false, so
we avoid caching as per 83116.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2018-01-25 Marek Polacek <pola...@redhat.com>
PR c++/83692
* constexpr.c (cxx_eval_store_expression): Clear constexpr_call_table.
* g++.dg/cpp1y/constexpr-83692.C: New test.
diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index 4d2ee4a28fc..0202d22f320 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -3663,6 +3663,10 @@ cxx_eval_store_expression (const constexpr_ctx *ctx,
tree t,
else
*valp = init;
+ /* We've rewritten a value of a temporary in this constexpr
+ context which might invalide a cached call. */
+ constexpr_call_table = NULL;
+
/* Update TREE_CONSTANT and TREE_SIDE_EFFECTS on enclosing
CONSTRUCTORs, if any. */
tree elt;
diff --git gcc/testsuite/g++.dg/cpp1y/constexpr-83692.C
gcc/testsuite/g++.dg/cpp1y/constexpr-83692.C
index e69de29bb2d..292ba7c22e9 100644
--- gcc/testsuite/g++.dg/cpp1y/constexpr-83692.C
+++ gcc/testsuite/g++.dg/cpp1y/constexpr-83692.C
@@ -0,0 +1,21 @@
+// PR c++/83692
+// { dg-do compile { target c++14 } }
+
+struct integer {
+ constexpr int value() const { return m_value; }
+ int m_value;
+};
+
+struct outer {
+ integer m_x{0};
+ constexpr outer()
+ {
+ if (m_x.value() != 0)
+ throw 0;
+ m_x.m_value = integer{1}.value();
+ if (m_x.value() != 1)
+ throw 0;
+ }
+};
+
+constexpr outer o{};
Marek
