[Issue 14937] New: Slow code compared to ldc/gdc on calculation with real variables

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14937

          Issue ID: 14937
           Summary: Slow code compared to ldc/gdc on calculation with real
                    variables
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: secondaryAccount at web.de

Created attachment 1542
  --> https://issues.dlang.org/attachment.cgi?id=1542&action=edit
benchmarked code

http://forum.dlang.org/thread/mqv2ct$1cpp$1@digitalmars.com?page=9#post-mr2ef5:241e2a:241:40digitalmars.com

The code is in the attachment.

Timings with some test input described below:
dmd -O -inline -release -noboundscheck              3700-3800 ms
gdc -O3 -march=native -frelease -fno-bounds-check   ~1000 ms
ldc2 -O3 -release -disable-boundscheck              ~800 ms

versions:
dmd 2.068
gdc based on 4.9.2
ldc 0.15.2beta1

OS: linux X86_64


Some notes:
- the benchmark is calling cosineSimilarity 1 million times with different
input and sum the return values (large text input file + IO functions omitted
here. I can add them if helpful.)
- timing with std.datetime around the loop - no IO included.
- pragma(inline, true) shows that dmd is unable to inline scalarProduct and
normSquared. disabling inlining for ldc causes no noticeable slowdown.
- elements of SparseVector are sorted by index.
- SparseVector.length is usually between 50 and 100 and maximal index is 47,000
- v1 and v2 are not pointing to the same data.
- gap between dmd and ldc/gdc is much smaller when replacing "real" with
double.

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