DMD is faster than LDC and GDC

[Daniel Kozak via Digitalmars-d]

V Thu, 12 Nov 2015 12:10:30 +0000
John Colvin via Digitalmars-d <digitalmars-d at puremagic.com> napsáno:

> On Thursday, 12 November 2015 at 11:59:50 UTC, Daniel Kozak wrote:
> > code:
> >
> > import std.stdio;
> >
> > auto fmttable(immutable(string[][]) table) {
> >
> >     import std.array : appender, uninitializedArray;
> >     import std.range : take, repeat;
> >     import std.exception : assumeUnique;
> >
> >     auto res = appender(uninitializedArray!(char[])(128));
> >     res.clear();
> >
> >     if (table.length == 0) return "";
> >     // column widths
> >     auto widths = new int[](table[0].length);
> >
> >     foreach (rownum, row; table) {
> >         foreach (colnum, cell; row) {
> >             if (cell.length > widths[colnum])
> >                 widths[colnum] = cast(int)cell.length;
> >         }
> >     }
> >
> >     foreach (row; table) {
> >         res ~= "|";
> >         foreach (colnum, cell; row) {
> >             int l = widths[colnum] - cast(int)cell.length;
> >             res ~= cell;
> >             if (l)
> >                 res ~= ' '.repeat().take(l);
> >             res ~= "|";
> >         }
> >         res.put("\n");
> >     }
> >
> >      return res.data.assumeUnique();
> > }
> >
> > void main() {
> >
> >     immutable table = [
> >         ["row1.1", "row1.2  ", "row1.3"],
> >         ["row2.1", "row2.2", "row2.3"],
> >         ["row3.1", "row3.2", "row3.3  "],
> >         ["row4.1", "row4.2", "row4.3"],
> >         ["row5.1", "row5.2", "row5.3"],
> >     ];
> >
> >     writeln(fmttable(table));
> >     int i;
> >     for (i=0; i < 1000000; ++i) {
> >         fmttable(table);
> >     }
> >     writeln(i);
> > }
> >
> > timings:
> >
> > DMD (-O -release -inline -boundscheck=off):
> > real	0m0.003s
> > user	0m0.000s
> > sys	0m0.000s
> >
> > LDMD2-ldc2 (-O -release -inline -boundscheck=off):
> > real	0m1.071s
> > user	0m1.067s
> > sys	0m0.000s
> >
> >
> > GDC (-O3 -finline -frelease -fno-bounds-check):
> > real	0m0.724s
> > user	0m0.720s
> > sys	0m0.003s  
> 
> What versions of these compilers? I suspect the majority (maybe 
> 80%-ish) of the time is spent allocating memory, so you might be 
> seeing GC improvements in recent DMD

DMD 2.069

LDC 2.067

GDC 2.065

No it is not cause by memory allocations.

It seems DMD can recognize that fmttable has same result every time, so
it does compute it only once.