[LLVMbugs] [Bug 2324] New: gvn non-local CSE miscompilation

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue May 13 04:53:21 PDT 2008


           Summary: gvn non-local CSE miscompilation
           Product: new-bugs
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: baldrick at free.fr
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=1645)
 --> (http://llvm.org/bugs/attachment.cgi?id=1645)
testcase .ll

The recent gvn non-local CSE changes broke several tests from the
Ada testsuite.  I reduced one down to the attached (but still large)
testcase.  The visible problem is that gvn thinks that the two memcmp
calls have the same results and eliminates one, but this is bogus
because %var_ara_8 changes between the two calls.

Reproduce using:
  opt -gvn
and observe the transformation of the memcpy calls.

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