[LLVMbugs] [Bug 23640] New: Fast isel causes: Assertion `MRI->getVRegDef(reg) && "Register use before def!"

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23640

            Bug ID: 23640
           Summary: Fast isel causes: Assertion `MRI->getVRegDef(reg) &&
                    "Register use before def!"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: hfinkel at anl.gov
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 14375
  --> https://llvm.org/bugs/attachment.cgi?id=14375&action=edit
bugpoint reduced test case

Run the attached (bugpoint-reduced) test case with:

  llc -O0 -relocation-model=pic < boost_O0_bug.ll

and with trunk you'll get:

llc: /src/llvm/lib/CodeGen/LiveVariables.cpp:133: void
llvm::LiveVariables::HandleVirtRegUse(unsigned int, llvm::MachineBasicBlock*,
llvm::MachineInstr*): Assertion `MRI->getVRegDef(reg) && "Register use before
def!"' failed.

It is complaining about this:

    Predecessors according to CFG: BB#5
    %vreg12<def> = IMPLICIT_DEF; G8RC:%vreg12
    %vreg11<def> = CMPD %vreg12, %vreg13; CRRC:%vreg11 G8RC:%vreg12,%vreg13
    BCC 68, %vreg11, <BB#9>; CRRC:%vreg11
    B <BB#7>


and it is indeed unclear where vreg13 is supposed to be defined (it is not
anywhere in the function).

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