• via Digitalmars-d-bugs (30/30) Apr 23 2016 https://issues.dlang.org/show_bug.cgi?id=15951

via Digitalmars-d-bugs <digitalmars-d-bugs puremagic.com> writes:

https://issues.dlang.org/show_bug.cgi?id=15951

          Issue ID: 15951
           Summary: Inefficiencies in struct initialization
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: andrei erdani.com

I list this as an enhancement but it's a blocker for RCStr, which has a
relatively large inline buffer (64 bytes). If that's compulsively initialized,
it makes RCStr nigh unusable as a competitive string.

The simplest case is an entirely uninitialized struct (with the equivalent C++
code):

https://godbolt.org/g/uItGGc
https://godbolt.org/g/6E1mkr

The initialization sequence of the D code is large and slow. What we really
want is to write a 0 in the last byte:

https://godbolt.org/g/twDGbP
https://godbolt.org/g/SRO5ql

Again the D version does a lot of unnecessary work. Where we want to get is
this:

https://godbolt.org/g/B0Xvq3
https://godbolt.org/g/OE6N8C

Here the D version should generate the same code as the C++ version.

--