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digitalmars.D.bugs - [Issue 942] New: a delegate defaults to 8 byte alignment when 4 byte is sufficient

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=942

           Summary: a delegate defaults to 8 byte alignment when 4 byte is
                    sufficient
           Product: D
           Version: 1.005
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: guido grumpy-cat.com


Delegate variables default to 8 byte alignment.  Delegates consist of two
pointer elements and should use 4 byte alignment instead.

The TypeDelegate struct does not override "unsigned alignsize()" from Type and
defaults to using "d_uns64 size(Loc loc)" to determine the alignment, which is
PTRSIZE * 2.  mtype.c could be updated as follows:

struct TypeDelegate : Type
{
    TypeDelegate(Type *t);
    Type *syntaxCopy();
    Type *semantic(Loc loc, Scope *sc);
    d_uns64 size(Loc loc);
+   unsigned alignsize();
    void toCBuffer2(OutBuffer *buf, Identifier *ident, HdrGenState *hgs);
    Expression *defaultInit();
    int isZeroInit();
    int checkBoolean();
    TypeInfoDeclaration *getTypeInfoDeclaration();
    Expression *dotExp(Scope *sc, Expression *e, Identifier *ident);
    int hasPointers();

    type *toCtype();
};

d_uns64 TypeDelegate::size(Loc loc)
{
    return PTRSIZE * 2;
}

+unsigned TypeDelegate::alignsize()
+{
+    // A Delegate consists of two ptr-sized values, so align it on pointer
size
+    // boundary
+    return PTRSIZE;
+}


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Feb 08 2007
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=942


bugzilla digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX




------- Comment #1 from bugzilla digitalmars.com  2007-03-20 02:35 -------
Doing this fix would break backwards compatibility, so I don't think this can
be changed at this point.


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Mar 20 2007
prev sibling next sibling parent d-bugmail puremagic.com writes:
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guido grumpy-cat.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|WONTFIX                     |




------- Comment #2 from guido grumpy-cat.com  2007-07-02 16:33 -------
Given all of the changes to D in 2.0, including adding new keywords, I don't
believe "breaking backwards compatibility" should be an issue.


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Jul 02 2007
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
                 CC|                            |clugdbug yahoo.com.au
         Resolution|                            |WONTFIX


--- Comment #3 from Don <clugdbug yahoo.com.au> 2010-08-13 22:35:16 PDT ---
Cases where Walter closes bugs as WONTFIX are so rare, that you have to respect
that.

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Aug 13 2010
prev sibling next sibling parent d-bugmail puremagic.com writes:
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nfxjfg gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nfxjfg gmail.com


--- Comment #4 from nfxjfg gmail.com 2010-08-13 22:58:30 PDT ---
(In reply to comment #1)

 Doing this fix would break backwards compatibility, so I don't think this can
 be changed at this point.


What backward compatibility? Show me the D code that can't simply be recompiled
using a fixed ABI.

Please be reminded that this would create stupid special cases in alternative
compiler implementations AND C headers which try to use D types containing
delegates.

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--- Comment #5 from Mark Guidarelli <guido grumpy-cat.com> 2010-08-13 23:52:24
PDT ---
I have long ago abandoned using D.  The fact that it took 3+ years to close
this bug (incorrectly I might add) validates I made the correct choice.  D is
nothing more than a play-thing for Walter, no serious commercial work will ever
be shipped using it.  I submitted many bug reports and patches all of which
were ignored by Walter.  I will spend my time improving viable projects like
LLVM and Google's Go.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #6 from bearophile_hugs eml.cc 2010-08-15 15:45:05 PDT ---
Answer to comment 3: It's true that WONTFIX from Walter are quite uncommon. But
here no enough explanations are given to why this change would break backwards
compatibility. So I think it's positive to have a bit of some more discussion
here.

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Aug 15 2010
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--- Comment #7 from Don <clugdbug yahoo.com.au> 2010-08-16 00:03:50 PDT ---
(In reply to comment #6)

 Answer to comment 3: It's true that WONTFIX from Walter are quite uncommon. But
 here no enough explanations are given to why this change would break backwards
 compatibility. So I think it's positive to have a bit of some more discussion
 here.


Yes. But reopening a WONTFIX bug just because you don't like the answer is
inappropriate. Frankly, I think it was exceedingly rude.
Note that there's nothing still open about this particular bug: Walter said no.
The deeper problem is the absence of a roadmap. Better would be to create a bug
report about the unambiguous state of the ABI. 

Note that this is a particularly dangerous breaking of the ABI: it silently
changes the generated code without warning. This makes it quite different to
things like name mangling changes, which always generate linking errors.
Nonetheless, the presence of bugs like bug 3398, which was only recently fixed,
does mean it's rather naive to think that the ABI is completely stable at
present.

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--- Comment #8 from bearophile_hugs eml.cc 2010-08-16 04:51:09 PDT ---
Don:


 But reopening a WONTFIX bug just because you don't like the answer is


inappropriate. Frankly, I think it was exceedingly rude.

I have just added a comment. I have not reopened it. I think that adding a
comment doesn't reopen the bug, so someone else has done it.

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--- Comment #9 from nfxjfg gmail.com 2010-08-16 09:56:25 PDT ---
(In reply to comment #7)

 Note that there's nothing still open about this particular bug: Walter said no.


Walter is wrong and the argument of binary compatibility is ridiculous. Little
issues like these should be resolved as quickly as possible because they are
annoying and only cause headaches for everyone. Maybe comment #5 isn't so wrong
here. There are many more issues similar to this bug report, and unlike this
bug, cause actual problems in practice. But Walter doesn't seem to care. Sucks
for the user, huh?


 Nonetheless, the presence of bugs like bug 3398, which was only recently fixed,
 does mean it's rather naive to think that the ABI is completely stable at
 present.


There you say it.

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