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[C++] PR 71737

Message ID bc5274be-ca09-812c-7b86-f4bf1dac8e6e@oracle.com
State New
Headers show

Commit Message

Paolo Carlini Jan. 13, 2017, 4:42 p.m. UTC 
Hi,

On 13/01/2017 15:51, Nathan Sidwell wrote:
> On 01/13/2017 09:45 AM, Paolo Carlini wrote:
>> Hi,
>>
>> in this error recovery issue get_underlying_template crashes when
>> TYPE_TEMPLATE_INFO_MAYBE_ALIAS is applied to a null orig_type. Simply
>> checking for that condition appears to solve the issue in a
>> straightforward way. Tested x86_64-linux.
>
> Wouldn't it be better if a scrogged alias got error_mark_node as the 
> underlying type?  (I have no idea whether that's an easy thing to 
> accomplish)
Your reply, Nathan, led me to investigate where exactly 
DECL_ORIGINAL_TYPE becomes null, and turns out that in tsubst_decl we 
have code actively doing that. That same code, a few lines below, only 
sets TYPE_DEPENDENT_P_VALID to false if type != error_mark_node. I 
cannot say to fully understand yet all the details, but certainly the 
patchlet below also passes testing. Do you have comments about this too?

Thanks!
Paolo.

///////////////////

Comments

Jason Merrill Jan. 13, 2017, 5:33 p.m. UTC | #1 
On Fri, Jan 13, 2017 at 11:42 AM, Paolo Carlini
<paolo.carlini@oracle.com> wrote:
> Hi,
>
> On 13/01/2017 15:51, Nathan Sidwell wrote:
>>
>> On 01/13/2017 09:45 AM, Paolo Carlini wrote:
>>>
>>> Hi,
>>>
>>> in this error recovery issue get_underlying_template crashes when
>>> TYPE_TEMPLATE_INFO_MAYBE_ALIAS is applied to a null orig_type. Simply
>>> checking for that condition appears to solve the issue in a
>>> straightforward way. Tested x86_64-linux.
>>
>>
>> Wouldn't it be better if a scrogged alias got error_mark_node as the
>> underlying type?  (I have no idea whether that's an easy thing to
>> accomplish)
>
> Your reply, Nathan, led me to investigate where exactly DECL_ORIGINAL_TYPE
> becomes null, and turns out that in tsubst_decl we have code actively doing
> that. That same code, a few lines below, only sets TYPE_DEPENDENT_P_VALID to
> false if type != error_mark_node. I cannot say to fully understand yet all
> the details, but certainly the patchlet below also passes testing. Do you
> have comments about this too?

The clearing of DECL_ORIGINAL_TYPE is to allow set_underlying_type to
then set it to something more appropriate.  That function currently
avoids setting DECL_ORIGINAL_TYPE to error_mark_node, perhaps that
should be changed.

Jason
diff mbox

Patch

Index: pt.c
===================================================================
--- pt.c	(revision 244405)
+++ pt.c	(working copy)
@@ -12868,7 +12868,8 @@  tsubst_decl (tree t, tree args, tsubst_flags_t com
 	/* Preserve a typedef that names a type.  */
 	if (is_typedef_decl (r))
 	  {
-	    DECL_ORIGINAL_TYPE (r) = NULL_TREE;
+	    if (type != error_mark_node)
+	      DECL_ORIGINAL_TYPE (r) = NULL_TREE;
 	    set_underlying_type (r);
 	    if (TYPE_DECL_ALIAS_P (r) && type != error_mark_node)
 	      /* An alias template specialization can be dependent