http://d.puremagic.com/issues/show_bug.cgi?id=1556

           Summary: Inefficient array concatenation (especially for 3+
                    arrays)
           Product: DGCC aka GDC
           Version: 0.24
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: glue layer
        AssignedTo: dvdfrdmn@users.sf.net
        ReportedBy: fvbommel@wxs.nl


GDC (0.24) compiles "a~b~c~d~e~f~g~h" (where all variables are arrays) to multiple invocations of _d_arraycatnT, a function which can handle any number of arrays but only seems to get called for two at a time. This causes N-1 function calls (each of which performs an allocation) instead of only one. This is inefficient and causes extra garbage on the heap.

GDC also generates calls to this multi-array function for a simple 2-array case, even though gphobos has _d_arraycatT especially for this purpose, without the overhead of vararg handling.

DMD (both 1.022 and 1.020 on which GDC 0.24 was based) does this right, calling _d_arraycatT for a 2-array concat and _d_arraycatnT to concatenate 3+ arrays.


Note: I'm tempted to add keyword "wrong-code" to this report, but the code *does* return the right result (an array filled with the concatenation of the initial arrays) so I'm not sure if it applies.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1556


dvdfrdmn@users.sf.net changed:

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




------- Comment #1 from dvdfrdmn@users.sf.net  2007-10-13 21:13 -------
Fixed in svn 185 / release 0.25


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