C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Marek Polacek]

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
calls itself on this new expr, then fold_sizeof_expr creates another SIZEOF_EXPR.
Then we call cxx_eval_constant_expression...

The call to cxx_eval_constant_expression is there to keep constexpr-vla1.C
working.  But we can avoid calling it in a template and it'll still work, and
we avoid this nasty recursion.

Bootstrapped/regtested on x86_64-linux, ok for trunk and 9?

2019-06-10  Marek Polacek  <polacek@redhat.com>

	PR c++/90825 - endless recursion when evaluating sizeof.
	* constexpr.c (cxx_eval_constant_expression): Don't recurse on the
	result of fold_sizeof_expr in a template.

	* g++.dg/cpp0x/constexpr-sizeof2.C: New test.

diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index a2f29694462..a68aac3b531 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -4808,9 +4808,13 @@ 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);
+      /* Don't recurse in a template, because then fold_sizeof_expr merely
+	 creates a new SIZEOF_EXPR, leading to an infinite recursion.  */
+      if (!processing_template_decl)
+	r = cxx_eval_constant_expression (ctx, r, lval,
+					  non_constant_p, overflow_p,
+					  jump_target);
       break;
 
     case COMPOUND_EXPR:
diff --git gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof2.C gcc/testsuite/g++.dg/cpp0x/constexpr-sizeof2.C
new file mode 100644
index 00000000000..2d3a169d28c
--- /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()];
+}

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Jakub Jelinek]

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.

>      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);
> +      /* Don't recurse in a template, because then fold_sizeof_expr merely
> +	 creates a new SIZEOF_EXPR, leading to an infinite recursion.  */
> +      if (!processing_template_decl)
> +	r = cxx_eval_constant_expression (ctx, r, lval,
> +					  non_constant_p, overflow_p,
> +					  jump_target);
>        break;

	Jakub

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Jason Merrill]

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.

Makes sense.  Also, cxx_sizeof_expr should probably only return a 
SIZEOF_EXPR if the operand is instantiation-dependent.

Jason

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Marek Polacek]

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?

Bootstrapped/regtested on x86_64-linux, ok for trunk and 9?

2019-06-11  Marek Polacek  <polacek@redhat.com>

	PR c++/90825 - 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.

	* g++.dg/cpp0x/constexpr-sizeof2.C: New test.

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;
+
       break;
 
     case COMPOUND_EXPR:
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()];
+}

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Jason Merrill]

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.

> Bootstrapped/regtested on x86_64-linux, ok for trunk and 9?
> 
> 2019-06-11  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/90825 - 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.
> 
> 	* g++.dg/cpp0x/constexpr-sizeof2.C: New test.
> 
> 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.

Jason

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Marek Polacek]

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  <polacek@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>{}), "" );
+ }
+};

Re: C++ PATCH for c++/90825 - endless recursion when evaluating sizeof

[Jason Merrill]

On 6/11/19 3:59 PM, Marek Polacek wrote:
> 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?

OK.

Jason