On Thu, Mar 24, 2022 at 11:40:11AM -0400, Jason Merrill wrote:
> On 3/18/22 17:55, Marek Polacek wrote:
> > On Fri, Mar 11, 2022 at 06:46:42PM -0500, Jason Merrill wrote:
> > > On 3/10/22 18:04, Marek Polacek wrote:
> > > > Since r9-6073 cxx_eval_store_expression preevaluates the value to
> > > > be stored, and that revealed a crash where a template code (here,
> > > > code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*.
> > > >
> > > > It happens because we're performing build_vec_init while processing
> > > > a template
> > >
> > > Hmm, that seems like the bug. Where's that call coming from?
> >
> > From build_aggr_init. So we're handling e.g.
> >
> > template<class>
> > constexpr void g () {
> > constexpr S s2[]{{'a'}};
> > }
> >
> > cp_finish_decl (decl=s2, init={{'a'}}) sees we're in
> > processing_template_decl,
> > but also that we have a constexpr var which is not dependent, nor is its
> > initializer:
> >
> > else if (init
> > && (init_const_expr_p || DECL_DECLARED_CONSTEXPR_P (decl))
> > && !TYPE_REF_P (type)
> > && decl_maybe_constant_var_p (decl)
> > && !(dep_init = value_dependent_init_p (init)))
> > {
> > /* This variable seems to be a non-dependent constant, so process
> > its initializer. If check_initializer returns non-null the
> > initialization wasn't constant after all. */
> > tree init_code;
> > cleanups = make_tree_vector ();
> > init_code = check_initializer (decl, init, flags, &cleanups);
> >
> > so we call check_initializer, where we go down this path:
> >
> > init_code = build_aggr_init_full_exprs (decl, init, flags);
> >
> > build_aggr_init sees that the type of 's2' is ARRAY_TYPE, so it calls
> > build_vec_init.
> >
> > I now recall that we've discussed build_vec_init in a template in the
> > past, for example in the context of c++/93676. So I agree we ought to
> > make an effort to avoid calling build_vec_init in a template. Perhaps
> > like this: use an INIT_EXPR. With that, we should call build_vec_init
> > if needed while instantiating. Does that make any sense?
>
> Hmm. If we do that, then we get back to
>
> > if (TREE_CODE (init_code) == INIT_EXPR)
>
> in check_initializer, and pull out the same init again, and set
> LOOKUP_ALREADY_DIGESTED. But I think that's wrong, we haven't digested it
> yet.
Yeah, that's probably no good :(
> Maybe we could avoid entering the below block of check_initializer at all in
> this situation?
>
> > if (((type_build_ctor_call (type) || CLASS_TYPE_P (type))
> > && !(flags & LOOKUP_ALREADY_DIGESTED)
> > && !(init && BRACE_ENCLOSED_INITIALIZER_P (init)
> > && CP_AGGREGATE_TYPE_P (type)
> > && (CLASS_TYPE_P (type)
>
> Maybe by adding || processing_template_decl here?
That seems to work! Thanks.
I've checked that we call build_vec_init when instantiating, so we
shouldn't be losing any of its effects.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Since r9-6073 cxx_eval_store_expression preevaluates the value to
be stored, and that revealed a crash where a template code (here,
code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*.
It happens because we're performing build_vec_init while processing
a template, which calls get_temp_regvar which creates an INIT_EXPR.
This INIT_EXPR's RHS contains an rvalue conversion so we create an
IMPLICIT_CONV_EXPR. Its operand is not type-dependent and the whole
INIT_EXPR is not type-dependent. So we call build_non_dependent_expr
which, with -fchecking=2, calls fold_non_dependent_expr. At this
point the expression still has an IMPLICIT_CONV_EXPR, which ought to
be handled in instantiate_non_dependent_expr_internal. However,
tsubst_copy_and_build doesn't handle INIT_EXPR; it will just call
tsubst_copy which does nothing when args is null. So we fail to
replace the IMPLICIT_CONV_EXPR and ICE.
The problem is that we call build_vec_init in a template in the
first place. We can avoid doing so by checking p_t_d before
calling build_aggr_init in check_initializer.
PR c++/104284
gcc/cp/ChangeLog:
* decl.cc (check_initializer): Don't call build_aggr_init in
a template.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-104284-1.C: New test.
* g++.dg/cpp1y/constexpr-104284-2.C: New test.
* g++.dg/cpp1y/constexpr-104284-3.C: New test.
* g++.dg/cpp1y/constexpr-104284-4.C: New test.
---
gcc/cp/decl.cc | 4 +++
.../g++.dg/cpp1y/constexpr-104284-1.C | 34 ++++++++++++++++++
.../g++.dg/cpp1y/constexpr-104284-2.C | 33 +++++++++++++++++
.../g++.dg/cpp1y/constexpr-104284-3.C | 33 +++++++++++++++++
.../g++.dg/cpp1y/constexpr-104284-4.C | 35 +++++++++++++++++++
5 files changed, 139 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 68741bbf5d2..69f60a6dc0f 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -7332,6 +7332,10 @@ check_initializer (tree decl, tree init, int flags,
vec<tree, va_gc> **cleanups)
&& !(init && BRACE_ENCLOSED_INITIALIZER_P (init)
&& CP_AGGREGATE_TYPE_P (type)
&& (CLASS_TYPE_P (type)
+ /* The call to build_aggr_init below could end up
+ calling build_vec_init, which may break when we
+ are processing a template. */
+ || processing_template_decl
|| !TYPE_NEEDS_CONSTRUCTING (type)
|| type_has_extended_temps (type))))
|| (DECL_DECOMPOSITION_P (decl) && TREE_CODE (type) == ARRAY_TYPE))
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C
new file mode 100644
index 00000000000..809c26a6161
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-1.C
@@ -0,0 +1,34 @@
+// PR c++/104284
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-fchecking=2" }
+
+struct S {
+ char c{};
+};
+
+auto x1 = [](auto) { constexpr S s[]{{}}; };
+auto x2 = [](auto) { constexpr S s[]{{'a'}}; };
+#if __cpp_designated_initializers >= 201707L
+auto x3 = [](auto) { constexpr S s[]{{.c = 'a'}}; };
+#endif
+auto x4 = [](auto) { constexpr S s[]{'a'}; };
+auto x5 = [](auto) { constexpr S s[]{{{}}}; };
+
+template<class>
+constexpr void g ()
+{
+ constexpr S s1[]{{}};
+ static_assert(s1[0].c == '\0', "");
+ constexpr S s2[]{{'a'}};
+ static_assert(s2[0].c == 'a', "");
+#if __cpp_designated_initializers >= 201707L
+ constexpr S s3[]{{.c = 'a'}};
+ static_assert(s3[0].c == 'a', "");
+#endif
+ constexpr S s4[]{'a'};
+ static_assert(s4[0].c == 'a', "");
+ constexpr S s5[]{{{}}};
+ static_assert(s5[0].c == '\0', "");
+}
+
+static_assert ((g<int>(), true), "");
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C
new file mode 100644
index 00000000000..704d37de129
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-2.C
@@ -0,0 +1,33 @@
+// PR c++/104284
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-fchecking=2" }
+
+struct S {
+ char a;
+ constexpr S() : a{'a'} { }
+ constexpr S(char a_) : a{a_} { }
+};
+
+auto x1 = [](auto) { constexpr S s[]{{}}; };
+auto x2 = [](auto) { constexpr S s[]{{'a'}}; };
+auto x3 = [](auto) { constexpr S s[]{'a'}; };
+auto x4 = [](auto) { constexpr S s[]{{{}}}; };
+
+template<typename>
+constexpr void g()
+{
+ constexpr S s1[]{{}};
+ static_assert(s1[0].a == 'a', "");
+ constexpr S s2[]{{'a'}};
+ static_assert(s2[0].a == 'a', "");
+ constexpr S s3[]{'a'};
+ static_assert(s3[0].a == 'a', "");
+ constexpr S s4[]{{{}}};
+ static_assert(s4[0].a == '\0', "");
+}
+
+void
+f ()
+{
+ g<int>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C
new file mode 100644
index 00000000000..6f23b255f9c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-3.C
@@ -0,0 +1,33 @@
+// PR c++/104284
+// { dg-do compile { target c++14 } }
+// { dg-additional-options "-fchecking=2" }
+// Like constexpr-104284.C, but the function template is not
+// constexpr. In that case, we were still calling build_vec_init
+// in a template, just not crashing.
+
+struct S {
+ char c{};
+};
+
+template<class>
+void g ()
+{
+ constexpr S s1[]{{}};
+ static_assert(s1[0].c == '\0', "");
+ constexpr S s2[]{{'a'}};
+ static_assert(s2[0].c == 'a', "");
+#if __cpp_designated_initializers >= 201707L
+ constexpr S s3[]{{.c = 'a'}};
+ static_assert(s3[0].c == 'a', "");
+#endif
+ constexpr S s4[]{'a'};
+ static_assert(s4[0].c == 'a', "");
+ constexpr S s5[]{{{}}};
+ static_assert(s5[0].c == '\0', "");
+}
+
+void
+f ()
+{
+ g<int>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C
b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C
new file mode 100644
index 00000000000..a99d3255a47
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-104284-4.C
@@ -0,0 +1,35 @@
+// PR c++/104284
+// { dg-do run { target c++14 } }
+// { dg-additional-options "-fchecking=2" }
+
+struct S {
+ char c{};
+};
+
+template<class>
+constexpr void g ()
+{
+ S s1[]{{}};
+ if (s1[0].c != '\0')
+ __builtin_abort ();
+ S s2[]{{'a'}};
+ if (s2[0].c != 'a')
+ __builtin_abort ();
+#if __cpp_designated_initializers >= 201707L
+ S s3[]{{.c = 'a'}};
+ if (s3[0].c != 'a')
+ __builtin_abort ();
+#endif
+ S s4[]{'a'};
+ if (s4[0].c != 'a')
+ __builtin_abort ();
+ S s5[]{{{}}};
+ if (s5[0].c != '\0')
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ g<int>();
+}
base-commit: 346ab5a54a831ad9c78afcbd8dfe98e0e07e3070
--
2.35.1
