[LLVMbugs] [Bug 4537] New: infinite loop in scev

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=4537

           Summary: infinite loop in scev
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Loop Optimizer
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nicholas at mxc.ca
                CC: gohman at apple.com, llvmbugs at cs.uiuc.edu


Created an attachment (id=3178)
 --> (http://llvm.org/bugs/attachment.cgi?id=3178)
testcase

$ opt -analyze -scalar-evolution b.bc -disable-output
Printing analysis 'Scalar Evolution Analysis' for function 'test':
Segmentation fault

I'll skip the nonsense and get straight to the infloopy part of the backtrace:

#19 0x082caa85 in llvm::ScalarEvolution::getSignExtendExpr (this=0x883e938, 
    Op=0x8841310, Ty=0x883b280) at ScalarEvolution.cpp:1000
#20 0x082c9070 in llvm::ScalarEvolution::createSCEV (this=0x883e938, 
    V=0x883fcec) at ScalarEvolution.cpp:2928
#21 0x082c9946 in llvm::ScalarEvolution::getSCEV (this=0x883e938, V=0x883fcec)
    at ScalarEvolution.cpp:2130
#22 0x082c807a in llvm::ScalarEvolution::createSCEV (this=0x883e938, 
    V=0x883fd30) at ScalarEvolution.cpp:2788
#23 0x082c9946 in llvm::ScalarEvolution::getSCEV (this=0x883e938, V=0x883fd30)
    at ScalarEvolution.cpp:2130
#24 0x082c9ea4 in llvm::ScalarEvolution::isNecessaryCond (this=0x883e938, 
    CondValue=0x8840008, Pred=llvm::CmpInst::ICMP_SGT, LHS=0x8841310, 
    RHS=0x8841594, Inverse=true) at ScalarEvolution.cpp:4530
#25 0x082c9b6f in llvm::ScalarEvolution::isNecessaryCond (this=0x883e938, 
    CondValue=0x8840098, Pred=llvm::CmpInst::ICMP_SGT, LHS=0x8841310, 
    RHS=0x8841594, Inverse=true) at ScalarEvolution.cpp:4449
#26 0x082ca327 in llvm::ScalarEvolution::isLoopBackedgeGuardedByCond (
    this=0x883e938, L=0x883df90, Pred=llvm::CmpInst::ICMP_SGT, LHS=0x8841310, 
    RHS=0x8841594) at ScalarEvolution.cpp:4395
#27 0x082caa85 in llvm::ScalarEvolution::getSignExtendExpr (this=0x883e938, 
    Op=0x8841310, Ty=0x883b280) at ScalarEvolution.cpp:1000

At #19, MaxBECount is i32 2147483646.
At #20, V and U are '%6 = sext i32 %5 to i64'.
At #23, V is %7 = udiv i64 undef, %6
At #24, PreCondLHS = %7, PreCondRHS = i64 0, Pred = ICMP_SGT.
At #25, BO is '%or.cond.i = or i1 %phitmp, %.not.i', LHS = '{(trunc i64 ((-1 *
%0) /u 8) to i32),+,-1}<bb4.i>', RHS = '-2147483648', Pred = ICMP_SGT and
Inverse = true.


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