[Issue 1923] New: GC optimization for contiguous pointers to the same page

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1923

           Summary: GC optimization for contiguous pointers to the same page
           Product: D
           Version: 1.028
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P3
         Component: Phobos
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: thecybershadow at gmail.com


Probably the best practical example for this situation is splitting a large
text file by whitespace: 

import std.file, std.string, std.gc;
import std.stdio: putr = writefln;
alias char[] string;
static import std.c.time;
double clock() {
    auto t = std.c.time.clock();
    return t/cast(double)std.c.time.CLOCKS_PER_SEC;
}
void main() {
  //disable;
  auto t0 = clock();
  auto txt = cast(string)read("text.txt"); // 6.3 MB of text
  auto t1 = clock();
  auto words = txt.split();
  auto t2 = clock();

  putr("loading time: ", t1 - t0); // 0.08 s
  putr("splitting time: ", t2 - t1); // 3.69 s with GC, 0.66 s without
  // Total running time with GC = 10.85 s
}

Example is from this NG post by bearophile: 

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=67673 

The attached patch increases the performance of this particular case tenfold by
my tests. It should have no significant overhead on other situations. There's a
bit more info in my reply to the abovementioned NG post.


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