[LLVMbugs] [Bug 20004] New: Performance regression when LTO is enabled

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20004

            Bug ID: 20004
           Summary: Performance regression when LTO is enabled
           Product: clang
           Version: 3.4
          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

Without LTO:

clang PerformanceTest.cpp dsp.cpp -std=c++11 -ffast-math -O3 -o PerformanceTest

Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.2.0
Thread model: posix

Iterations: 955
C results: 100,043,846 shorts per second.

With LTO:

clang PerformanceTest.cpp dsp.cpp -std=c++11 -ffast-math -flto -O3 -o
PerformanceTest

Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.2.0
Thread model: posix

Iterations: 586
C results: 61,349,033 shorts per second.

Code can be downloaded from here:
https://gist.github.com/learnopengles/004ff4eee75057ca006c

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