[LLVMbugs] [Bug 4599] New: opt -O1 introduces umax expressions in simple for loops

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue Jul 21 03:21:53 PDT 2009


           Summary: opt -O1 introduces umax expressions in simple for loops
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: edwintorok at gmail.com
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=3230)
 --> (http://llvm.org/bugs/attachment.cgi?id=3230)

$ opt -scalar-evolution -analyze y.bc
Loop for.cond: backedge-taken count is %ecx
Loop for.cond: max backedge-taken count is -1

If I run -O1 I get a much uglier form for the loop:

$ opt -O1 -scalar-evolution y.bc -analyze
Loop for.body: backedge-taken count is (-1 + (1 umax %ecx))
Loop for.body: max backedge-taken count is (-1 + (1 umax %ecx))

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