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D.gnu - [Issue 1556] New: Inefficient array concatenation (especially for 3+ arrays)

reply d-bugmail puremagic.com writes:

           Summary: Inefficient array concatenation (especially for 3+
           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.

Oct 08 2007
parent d-bugmail puremagic.com writes:

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

Oct 13 2007