[LLVMbugs] [Bug 22657] New: clang compiled c-ray 1.1 benchmarks up to 43% slower than gcc compiled versions

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22657

            Bug ID: 22657
           Summary: clang compiled c-ray 1.1 benchmarks up to 43% slower
                    than gcc compiled versions
           Product: clang
           Version: 3.6
          Hardware: Macintosh
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: howarth.mailing.lists at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The c-ray 1.1 benchmark, from
http://www.phoronix-test-suite.com/benchmark-files/c-ray-1.1.tar.gz, exhibits
up to 43% slower performance when compiled under clang compared to when
compiled with gcc. Using "-O3 -march=native" on a Nehalem processor, the
following is observed...

clang 3.5.1
% ./RUN.full
c-ray-mt v1.1
Rendering took: 0 seconds (50 milliseconds)
c-ray-mt v1.1
Rendering took: 0 seconds (865 milliseconds)
c-ray-mt v1.1
Rendering took: 11 seconds (11254 milliseconds)
c-ray-mt v1.1
Rendering took: 2 seconds (2660 milliseconds)

clang 3.6-rc4
% ./RUN.full
c-ray-mt v1.1
Rendering took: 0 seconds (52 milliseconds)
c-ray-mt v1.1
Rendering took: 1 seconds (1054 milliseconds)
c-ray-mt v1.1
Rendering took: 13 seconds (13556 milliseconds)
c-ray-mt v1.1
Rendering took: 2 seconds (2850 milliseconds)

clang 3.7svn (r230135)
% ./RUN.full
c-ray-mt v1.1
Rendering took: 0 seconds (51 milliseconds)
c-ray-mt v1.1
Rendering took: 1 seconds (1051 milliseconds)
c-ray-mt v1.1
Rendering took: 13 seconds (13783 milliseconds)
c-ray-mt v1.1
Rendering took: 2 seconds (2863 milliseconds)

gcc 4.9.2
% ./RUN.full
c-ray-mt v1.1
Rendering took: 0 seconds (43 milliseconds)
c-ray-mt v1.1
Rendering took: 0 seconds (689 milliseconds)
c-ray-mt v1.1
Rendering took: 8 seconds (8786 milliseconds)
c-ray-mt v1.1
Rendering took: 2 seconds (2478 milliseconds)

gcc 5.0svn (r220888)
% ./RUN.full
c-ray-mt v1.1
Rendering took: 0 seconds (45 milliseconds)
c-ray-mt v1.1
Rendering took: 0 seconds (667 milliseconds)
c-ray-mt v1.1
Rendering took: 8 seconds (8727 milliseconds)
c-ray-mt v1.1
Rendering took: 2 seconds (2390 milliseconds)

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