[LLVMbugs] [Bug 22120] New: redundant clrlwi on powerpc64

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Wed Jan 7 10:47:09 PST 2015


            Bug ID: 22120
           Summary: redundant clrlwi on powerpc64
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: skvadrik at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13648
  --> http://llvm.org/bugs/attachment.cgi?id=13648&action=edit
1.c and 2.c

See files 1.cpp and 2.cpp in attach.

compile: (clang version 3.6.0)

$ clang++ -target powerpc64-unknown-linux-gnu -g -O2 -c 1.c
$ clang++ -target powerpc64-unknown-linux-gnu -g -O2 -c 2.c

disassemble: (GNU objdump (GNU Binutils) 2.24)

$ powerpc64-unknown-linux-gnu-objdump -d 1.o > 1.s
$ powerpc64-unknown-linux-gnu-objdump -d 2.o > 2.s

compare 1.s and 2.s and you'll find redundant instruction
    clrlwi r6,r6,24
in 2.s.

Both files are cut down from real-life programs.

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