On Tue, Jun 11, 2019 at 03:05:26PM -0400, Jason Merrill wrote:
> On 6/11/19 2:28 PM, Marek Polacek wrote:
> > On Tue, Jun 11, 2019 at 08:37:27AM -0400, Jason Merrill wrote:
> > > On 6/11/19 7:47 AM, Jakub Jelinek wrote:
> > > > On Mon, Jun 10, 2019 at 09:59:46PM -0400, Marek Polacek wrote:
> > > > > This test segvs since r269078, this hunk in particular:
> > > > >
> > > > > @@ -4581,8 +4713,9 @@ cxx_eval_constant_expression (const
> > > > > constexpr_ctx *ctx, tree t,
> > > > > break;
> > > > >
> > > > > case SIZEOF_EXPR:
> > > > > - r = fold_sizeof_expr (t);
> > > > > - VERIFY_CONSTANT (r);
> > > > > + r = cxx_eval_constant_expression (ctx, fold_sizeof_expr (t),
> > > > > lval,
> > > > > + non_constant_p, overflow_p,
> > > > > + jump_target);
> > > > > break;
> > > > >
> > > > > In a template, fold_sizeof_expr will just create a new SIZEOF_EXPR,
> > > > > that is the
> > > > > same, but not identical; see cxx_sizeof_expr. Then
> > > > > cxx_eval_constant_expression
> > > >
> > > > Not always, if it calls cxx_sizeof_expr, it will, but if it calls
> > > > cxx_sizeof_or_alignof_type it will only if the type is dependent or VLA.
> > > >
> > > > So, I'd think you should call cxx_eval_constant_expression if TREE_CODE
> > > > (r)
> > > > != SIZEOF_EXPR, otherwise probably *non_constant_p = true; is in order,
> > > > maybe together with gcc_assert (ctx->quiet); ? I'd hope that if we
> > > > really
> > > > require a constant expression we evaluate it in
> > > > !processing_template_decl
> > > > contexts.
> >
> > Ok, I had been meaning to add the *non_constant_p bit but never did. :(
> >
> > > Makes sense. Also, cxx_sizeof_expr should probably only return a
> > > SIZEOF_EXPR if the operand is instantiation-dependent.
> >
> > That results in
> >
> > FAIL: g++.dg/template/incomplete6.C -std=c++98 (internal compiler error)
> > FAIL: g++.dg/template/incomplete6.C -std=c++98 (test for excess errors)
> > FAIL: g++.dg/template/overload13.C -std=c++98 (internal compiler error)
> > FAIL: g++.dg/template/overload13.C -std=c++98 (test for excess errors)
> >
> > because we trigger an assert in value_dependent_expression_p:
> >
> > /* If there are no operands, it must be an expression such
> > as "int()". This should not happen for aggregate types
> > because it would form non-constant expressions. */
> > gcc_assert (cxx_dialect >= cxx11
> > || INTEGRAL_OR_ENUMERATION_TYPE_P (type));
> >
> > return false;
> >
> > and in this case we have T() where T is a class, and it's in C++98.
> >
> > It's not needed to fix this PR so perhaps the following could go in,
> > but is there anything I should do about that?
>
> instantiation_dependent_uneval_expression_p shouldn't have that problem.
Ah, nice.
> > diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
> > index a2f29694462..443e1c7899f 100644
> > --- gcc/cp/constexpr.c
> > +++ gcc/cp/constexpr.c
> > @@ -4808,9 +4808,16 @@ cxx_eval_constant_expression (const constexpr_ctx
> > *ctx, tree t,
> > break;
> > case SIZEOF_EXPR:
> > - r = cxx_eval_constant_expression (ctx, fold_sizeof_expr (t), lval,
> > - non_constant_p, overflow_p,
> > - jump_target);
> > + r = fold_sizeof_expr (t);
> > + /* In a template, fold_sizeof_expr may merely create a new
> > SIZEOF_EXPR,
> > + which could lead to an infinite recursion. */
> > + if (TREE_CODE (r) != SIZEOF_EXPR)
> > + r = cxx_eval_constant_expression (ctx, r, lval,
> > + non_constant_p, overflow_p,
> > + jump_target);
> > + else
> > + *non_constant_p = true;
>
> Let's also add the assert Jakub suggested.
Done.
Luckily, this also fixed c++/90832 so I'm adding a test for that, too.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-06-11 Marek Polacek <pola...@redhat.com>
PR c++/90825 - endless recursion when evaluating sizeof.
PR c++/90832 - endless recursion when evaluating sizeof.
* constexpr.c (cxx_eval_constant_expression): Don't recurse on the
result of fold_sizeof_expr if is returns a SIZEOF_EXPR.
* typeck.c (cxx_sizeof_expr): Only return a SIZEOF_EXPR if the operand
is instantiation-dependent.
* g++.dg/cpp0x/constexpr-sizeof2.C: New test.
* g++.dg/cpp0x/constexpr-sizeof3.C: New test.
diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index a2f29694462..80eaffdb33f 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -4808,9 +4808,19 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx,
tree t,
break;
case SIZEOF_EXPR:
- r = cxx_eval_constant_expression (ctx, fold_sizeof_expr (t), lval,
- non_constant_p, overflow_p,
- jump_target);
+ r = fold_sizeof_expr (t);
+ /* In a template, fold_sizeof_expr may merely create a new SIZEOF_EXPR,
+ which could lead to an infinite recursion. */
+ if (TREE_CODE (r) != SIZEOF_EXPR)
+ r = cxx_eval_constant_expression (ctx, r, lval,
+ non_constant_p, overflow_p,
+ jump_target);
+ else
+ {
+ *non_constant_p = true;
+ gcc_assert (ctx->quiet);
+ }
+
break;
case COMPOUND_EXPR:
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index 154da59627b..a8fb1624b48 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -1690,7 +1690,7 @@ cxx_sizeof_expr (tree e, tsubst_flags_t complain)
if (e == error_mark_node)
return error_mark_node;
- if (processing_template_decl)
+ if (instantiation_dependent_uneval_expression_p (e))
{
e = build_min (SIZEOF_EXPR, size_type_node, e);
TREE_SIDE_EFFECTS (e) = 0;
diff --git gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof2.C
gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof2.C
new file mode 100644
index 00000000000..8676ae40b61
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof2.C
@@ -0,0 +1,14 @@
+// PR c++/90825 - endless recursion when evaluating sizeof.
+// { dg-do compile { target c++11 } }
+
+class address {
+ char host_[63];
+public:
+ static constexpr unsigned buffer_size() noexcept { return sizeof(host_); }
+};
+
+template <class Archive>
+void load()
+{
+ char host[address::buffer_size()];
+}
diff --git gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof3.C
gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof3.C
new file mode 100644
index 00000000000..05f07c38796
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof3.C
@@ -0,0 +1,22 @@
+// PR c++/90832 - endless recursion when evaluating sizeof.
+// { dg-do compile { target c++11 } }
+
+class B
+{
+ template <typename T> friend struct A;
+ B() {}
+};
+
+template <typename T>
+struct A
+{
+ A() noexcept(sizeof(B{})) { }
+};
+
+struct C
+{
+ C()
+ {
+ static_assert( sizeof(A<int>{}), "" );
+ }
+};
