RFR(S): 8138890: C1: Ambiguous operator delete

Mon Oct 12 09:14:08 UTC 2015

Hi Christian,

seems like VALUE_OBJ_CLASS_SPEC inherits from _ValueObj on platforms on which the compiler uses empty base class optimization.
On these platforms, the inheritance comes for free (no extra size for the object).
A problem is that the macro VALUE_OBJ_CLASS_SPEC does not work for multi-inheritance because it translates to either nothing or a term which would need comma separation.

The other class we inherit from defines new/delete operators which are not supposed to get used for this derived class, so I think making these operators private there is just the right thing to do.

Best regards,
  Martin

From: Christian Thalinger [mailto:christian.thalinger at oracle.com]
Sent: Samstag, 10. Oktober 2015 00:32
To: Doerr, Martin
Cc: Volker Simonis; Lindenmaier, Goetz; Mikael Gerdin; hotspot compiler
Subject: Re: RFR(S): 8138890: C1: Ambiguous operator delete

On Oct 9, 2015, at 9:08 AM, Doerr, Martin <martin.doerr at sap.com<mailto:martin.doerr at sap.com>> wrote:

Hi Christian,

I have just added comments. We can also get rid of the multi-inheritance in RanceCheckEliminator::Verification.

Hmm.  Why did we have it this way (not using the macro and such)?

-  class Verification : public _ValueObj /*VALUE_OBJ_CLASS_SPEC*/, public BlockClosure {

+  class Verification : public BlockClosure {

The new webrev is:
http://cr.openjdk.java.net/~mdoerr/8138890_c1_ambiguous_delete/webrev.03

Best regards,
  Martin

From: Christian Thalinger [mailto:christian.thalinger at oracle.com]
Sent: Freitag, 9. Oktober 2015 20:35
To: Doerr, Martin
Cc: Volker Simonis; Lindenmaier, Goetz; Mikael Gerdin; hotspot compiler
Subject: Re: RFR(S): 8138890: C1: Ambiguous operator delete

On Oct 9, 2015, at 12:03 AM, Doerr, Martin <martin.doerr at sap.com<mailto:martin.doerr at sap.com>> wrote:

Hi,

thanks for reviewing.
As requested by Götz, I just removed the second ‘private’.
The new webrev is here:
http://cr.openjdk.java.net/~mdoerr/8138890_c1_ambiguous_delete/webrev.02

Looks good.  Can we add a comment saying that objects of this class should never be allocated on the heap or something?

Best regards,
  Martin

From: Volker Simonis [mailto:volker.simonis at gmail.com]
Sent: Mittwoch, 7. Oktober 2015 21:28
To: Doerr, Martin
Cc: Mikael Gerdin; Christian Thalinger; hotspot compiler
Subject: Re: RFR(S): 8138890: C1: Ambiguous operator delete

Hi Martin,

as the new/delete operators in StackObj are private (I missed that before) they shouldn't be visible in LIRGenerator. So this is probably yet another xlC bug :(
On the other hand the new/delete operators in CompilationResourceObject are public and are inherited by LIRGenerator. So if we only want to generate LIRGenerator instances on the stack, your change is good, because it ensures this. And in that case we surely don't need an implementation.

So thumbs up from me!

Volker

On Wednesday, October 7, 2015, Doerr, Martin <martin.doerr at sap.com<mailto:martin.doerr at sap.com>> wrote:
Hi Volker,

the C1 classes we are talking about should never get instantiated by operator new.
A typical way to establish this is to make the new operators private.

I don’t really care if the delete operators are public or private because if the new operator is never used, how can the delete operator get used?
It may be more beautiful to declare them as private as well. Only in the case Götz has showed, some Compilers reject the private delete operators.

Best regards,
Martin

From: Volker Simonis [mailto:volker.simonis at gmail.com]
Sent: Mittwoch, 7. Oktober 2015 17:57
To: Mikael Gerdin
Cc: Doerr, Martin; Christian Thalinger; hotspot compiler
Subject: Re: RFR(S): 8138890: C1: Ambiguous operator delete

Hi Martin,
we have:
class LIRGenerator: public InstructionVisitor, public BlockClosure

and:

class BlockClosure: public CompilationResourceObj

class CompilationResourceObj ALLOCATION_SUPER_CLASS_SPEC {
 public:
  void* operator new(size_t size) throw() { return Compilation::current()->arena()->Amalloc(size); }
  void* operator new(size_t size, Arena* arena) throw() {
    return arena->Amalloc(size);
  }
  void  operator delete(void* p) {} // nothing to do
};

class InstructionVisitor: public StackObj

class StackObj ALLOCATION_SUPER_CLASS_SPEC {
 private:
  void* operator new(size_t size) throw();
  void* operator new [](size_t size) throw();
#ifdef __IBMCPP__
 public:
#endif
  void  operator delete(void* p);
  void  operator delete [](void* p);
Now you declare new "new()" and "delete()" operators in the LIRGenerator which will actually hide the corresponding operators from the base classes. You also provide no implementation for the new operators in LIRGenerator. So which new/delete operators will be actually used for allocating new LIRGenerator instances?
OK, wait. As far as I can see, LIRGenerator is never dynamically allocated, right? In that case it should be a StackObj and you could probably solve the problem with "using" directives (e.g. using StackObj::operator new, ...). Have you tried that?
Regards,
Volker

On Wed, Oct 7, 2015 at 4:55 PM, Mikael Gerdin <mikael.gerdin at oracle.com<mailto:mikael.gerdin at oracle.com>> wrote:
On 2015-10-07 16:17, Doerr, Martin wrote:
Hi,

that’s a good question J

I can only remember that there were problems with some old compilers.

Anyway, xlC 12.1 can deal with the private delete operators.

If that's the case, can we also get rid of the workaround in allocation.hpp?

Thanks
/Mikael

Here’s the new webrev:

http://cr.openjdk.java.net/~mdoerr/8138890_c1_ambiguous_delete/webrev.01

Best regards,

   Martin

*From:*Christian Thalinger [mailto:christian.thalinger at oracle.com]
*Sent:* Mittwoch, 7. Oktober 2015 03:32
*To:* Doerr, Martin
*Cc:* hotspot compiler
*Subject:* Re: RFR(S): 8138890: C1: Ambiguous operator delete

    On Oct 6, 2015, at 3:56 AM, Doerr, Martin <martin.doerr at sap.com
    <mailto:martin.doerr at sap.com<mailto:martin.doerr at sap.com%0b%20%20%20%20%3cmailto:martin.doerr at sap.com>>> wrote:

    Hi,

    xlC on AIX rejects to compile LIRGenerator and
    RangeCheckEliminator::Verification due to ambiguous operator delete
    which gets inherited from multiple base classes.

    This change is a prerequisite for our C1 on PPC64 contribution.

    Webrev is here:

    http://cr.openjdk.java.net/~mdoerr/8138890_c1_ambiguous_delete/webrev.00

Let me ask my question here:  why do you need the delete methods to be
public on AIX?

Please review this change.  I need a sponsor, please.

Best regards,

   Martin

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/attachments/20151012/599ff56d/attachment-0001.html>