[Issue 4440] New: inlined delegates produces different asm than straight lined code

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4440

           Summary: inlined delegates produces different asm than straight
                    lined code
           Product: D
           Version: D1 & D2
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: braddr at puremagic.com


--- Comment #0 from Brad Roberts <braddr at puremagic.com> 2010-07-08 22:59:51 PDT ---
split from bug 859:

Leandro Lucarella      2010-06-27 18:49:49 PDT 

I'm having some performance problems moving some stuff from a lower-level
C-style to a higher-lever D-style. Here is an example:

---
int find_if(bool delegate(ref int) predicate)
{
        for (int i = 0; i < 100; i++)
                if (predicate(i))
                        return i;
        return -1;
}

int main()
{
//      for (int i = 0; i < 100; i++)
//              if (i == 99)
//                      return i;
//      return -1;
        return find_if((ref int i) { return i == 99; });
}
---

The program produced by this source executes 4 times more instructions than the
more direct (lower-level) version commented out. I would expect DMD to inline
all functions/delegates and produce the same asm for both, but that's not the
case.

This is a reduced test-case, but I'm working on improving the GC and I'm really
hitting this problem. If I use this higher-level style in the GC, a Dil run for
generating the Tango docs is 3.33 times slower than the C-ish style used by the
current GC.

So I think this is a real problem for D, it's really important to be able to
encourage people to use the higher-level D constructs.

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