[LLVMbugs] [Bug 2295] New: incorrect optimization (instcombine)

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Wed May 7 15:41:31 PDT 2008


           Summary: incorrect optimization (instcombine)
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: scott.llvm at h4ck3r.net
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=1621)
 --> (http://llvm.org/bugs/attachment.cgi?id=1621)
.ll to demonstrate mis-optimization

Using LLVM 2.2:

llvm-as -f x.ll
opt -instcombine -f x.bc -o x.opt.bc
lli x.bc
lli x.opt.bc

The first outputs (as expected):
90 (Z)
and the second (optimized) incorrectly outputs:
33 (!)

I was unable to get bugpoint to work, but the attached file has been manually
minimized (73 lines). Happens with "opt -std-compile-opts" also, but "opt
-instcombine" is all that's necessary.

It appears two different pointers into allocated memory are being conflated.

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