[LLVMbugs] [Bug 22616] New: Performance degradations of several tests from eembc.2.0 suite and Coremark suite on x86 Avoton-1.7 due to ‘?=[SimplifyCFG]=?UTF-8?Q? Be more aggressive’

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22616

            Bug ID: 22616
           Summary: Performance degradations of several tests from
                    eembc.2.0 suite and Coremark suite on x86 Avoton-1.7
                    due to ‘[SimplifyCFG] Be more aggressive’
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: sergey.k.okunev at gmail.com
                CC: david.l.kreitzer at intel.com, denis.briltz at intel.com,
                    elena.demikhovsky at intel.com, james.molloy at arm.com,
                    llvmbugs at cs.uiuc.edu, michael.m.kuperstein at intel.com,
                    sergos.gnu at gmail.com, zia.ansari at intel.com
    Classification: Unclassified

While our performance testing  regressions on tests rgbcmykv2 (more than 20%),
mp4decod, mp2enf32, mp2enfix from eembc.2.0 suite and Coremark test were
detected. Bisect analysis showed LLVM revision 229099 is responsible for these
degradations. This revision enabled ‘[SimplifyCFG] Be more aggressive’ as
described in comments.

commit c76bff0715a253321a33287d8dc319e08f6fee8b
Author: James Molloy <james.molloy at arm.com>
Date:   Fri Feb 13 10:48:30 2015 +0000

    [SimplifyCFG] Be more aggressive

    Up the phi node folding threshold from a cheap "1" to a meagre "2".

    Update tests for extra added selects and slight code churn.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229099
91177308-0d34-0410-b5e6-96231b3b80d8

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