[llvm-bugs] [Bug 39554] New: Add a unit test for frame index expansion

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39554

            Bug ID: 39554
           Summary: Add a unit test for frame index expansion
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: AVR
          Assignee: unassignedbugs at nondot.org
          Reporter: me at dylanmckay.io
                CC: llvm-bugs at lists.llvm.org

In avr-rust bug #112, we encountered a backend bug caused by invalid expansion
of a FRMIDX instruction into a MOVWRdRr instruction. The backend would leave an
extraneous operand from the original FRMIDX that was not consistent with the
definition of MOVWRdRr.

This would trigger an assertion:

    Assertion failed: ((isImpReg || Op.isRegMask() || MCID->isVariadic() ||
                        OpNo < MCID->getNumOperands() || isMetaDataOp) &&
                        "Trying to add an operand to a machine instr that is
already done!"),
    function addOperand, file llvm/lib/CodeGen/MachineInstr.cpp


More informatiob about that bug can be found at:
https://github.com/avr-rust/rust/issues/112

We should write unit tests that cover the expansion of FRMIDX nodes into
MOVWRdRr instructions.

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