[LLVMbugs] [Bug 24171] New: [AArch64] 403050abcc091260be2e8f58484e7a39c0782b47 increased Spill/Reload/ by 5 times

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=24171

            Bug ID: 24171
           Summary: [AArch64] 403050abcc091260be2e8f58484e7a39c0782b47
                    increased Spill/Reload/ by 5 times
           Product: tools
           Version: trunk
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: opt
          Assignee: unassignedbugs at nondot.org
          Reporter: lawrence at codeaurora.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

For open source bzip2/decompress.c

The following commit

commit 403050abcc091260be2e8f58484e7a39c0782b47
Author: Daniel Berlin <dberlin at dberlin.org>
Date:   Tue Feb 3 20:37:08 2015 +0000

    Allow PRE to insert no-cost phi nodes

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228024
91177308-0d34-0410-b5e6-96231b3b80d8

Transformed a lot of 

x=  GEP base, constant, constant  

==>

x.pre = PHI .......


Which introduced  two new long live range (base is live anyway) for each of
those GEP.

Bzip2/decompress originally has a lot of long live range already, this
transformation brought in even more, which increased the number of Spill/Reload
from 5xx to 3xxx.

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