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: [email protected]
Reporter: [email protected]
CC: [email protected]
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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