[LLVMbugs] [Bug 23619] New: Performance regression versus GCC 4.9.1 -- test case and ASM attached

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23619

            Bug ID: 23619
           Summary: Performance regression versus GCC 4.9.1 -- test case
                    and ASM attached
           Product: clang
           Version: 3.6
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: learnopengles at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 14358
  --> https://llvm.org/bugs/attachment.cgi?id=14358&action=edit
Compiler-generated ASM

With the attached code, the gcc version is 20% faster than the clang version.

clang++
--------
clang++ --version
Apple LLVM version 6.1.0 (clang-602.0.49) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

clang++ -std=c++11 -O2 dsp.cpp main.cpp -o dsp && ./dsp
85,758,063 shorts/second

gcc
--------
gcc-mp-4.9 --version
gcc-mp-4.9 (MacPorts gcc49 4.9.2_1) 4.9.2

gcc-mp-4.9 -std=c++11 -O2 dsp.cpp main.cpp -o dsp && ./dsp
102,104,163 shorts/second

Source code: https://gist.github.com/anonymous/fd213a7b8ffdcfd219dc
Compiler-generated ASM attached.

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