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digitalmars.D.bugs - [Issue 3490] New: DMD Never Inlines Functions that Could Throw

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3490

           Summary: DMD Never Inlines Functions that Could Throw
           Product: D
           Version: 2.036
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: performance
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: dsimcha yahoo.com


--- Comment #0 from David Simcha <dsimcha yahoo.com> 2009-11-09 06:26:18 PST ---
Here's an absurdly simple test program.  enforceStuff() does not get inlined,
as the disassembly below shows.  I couldn't find anything about exceptions in
inline.c, but if this doesn't get inlined, I assume nothing that could throw
ever does.  

This severely affects the performance of std.range, since Andrei uses enforce()
all over the place, causing lots of stuff not to be inlined.  For example, I
read disassemblies involving std.range.Take and it seems like Take.popFront()
and Take.front() are never inlined.

void main() {
    enforceStuff(1);
}

void enforceStuff(uint num) {  // Not inlined.
   if(num == 0) {
       throw new Exception("");
   }
}

Disassembly of main():

__Dmain PROC NEAR
;  COMDEF __Dmain
        push    eax                                     ; 0000 _ 50
        mov     eax, 1                                  ; 0001 _ B8, 00000001
        call    _D5test812enforceStuffFkZv              ; 0006 _ E8,
00000000(rel)
        xor     eax, eax                                ; 000B _ 31. C0
        pop     ecx                                     ; 000D _ 59
        ret                                             ; 000E _ C3
__Dmain ENDP

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3490


Ary Borenszweig <ary esperanto.org.ar> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ary esperanto.org.ar


--- Comment #1 from Ary Borenszweig <ary esperanto.org.ar> 2009-11-09 06:32:37
PST ---
Here's why:

int Statement::inlineCost(InlineCostState *ics)
{
    return COST_MAX;        // default is we can't inline it
}

and ThrowStatement never overrides it.

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Leandro Lucarella <llucax gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |llucax gmail.com
             Blocks|                            |859


--- Comment #2 from Leandro Lucarella <llucax gmail.com> 2010-07-08 06:54:15
PDT ---
I'm marking this a a blocker of bug 859 so there is a single bug to track all
the inlining issues. Please do the same if you open more bugs associated to
inlining, or post them directly in bug 859.

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Brad Roberts <braddr puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |braddr puremagic.com
             Blocks|859                         |


--- Comment #3 from Brad Roberts <braddr puremagic.com> 2010-07-08 22:47:07 PDT
---
undoing false dependency

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--- Comment #4 from Leandro Lucarella <llucax gmail.com> 2010-07-09 06:14:20
PDT ---
(In reply to comment #3)

 undoing false dependency



Can you elaborate a little on why having bug 859 as a tracker of all missing
inline oportunities is a bad thing?

Thanks

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prev sibling parent Brad Roberts <braddr puremagic.com> writes:
On 7/9/2010 6:17 AM, d-bugmail puremagic.com wrote:

 http://d.puremagic.com/issues/show_bug.cgi?id=3490
 
 
 
 --- Comment #4 from Leandro Lucarella <llucax gmail.com> 2010-07-09 06:14:20
PDT ---
 (In reply to comment #3)

 undoing false dependency



 Can you elaborate a little on why having bug 859 as a tracker of all missing
 inline oportunities is a bad thing?
 
 Thanks
 



Replying outside bugzilla, no reason to clutter up all those reports with more
stuff unrelated to the specifics of the reports themselves.

Using a real report as a tracker is almost always a bad idea.  Using this case
as an example and assuming that 859 was an inlining bug:  What's the right thing
to do when 859's issue is fixed but all the rest aren't?  If it wasn't a
tracker, the right thing would be to close 859 and move on.  But trackers should
only be closed when all the depends-on's are fixed.  See the problem?

The next reason that it's a bad idea is that 859 isn't a missed inline
opportunity.  The code in question is inlined.  Something else in in play --
still looking into it.  So, fixed or not, the depend-on's aren't accurate any
more either.. or at least some aren't.

I'm also of the general opinion that trackers aren't generally useful either,
but in this case it goes beyond that.  Inlining bugs are easy to locate with the
search feature.. just search for all bugs with inline in the subject.  Done. 
Easy.

That help?

Later,
Brad
Jul 09 2010