Extended Description

For this program:

$ cat b.ll
define i64 @​bork(<2 x i64> %vec) {
entry:
%tmp = extractelement <2 x i64> %vec, i32 0
ret i64 %tmp
}

I get this abort:

$ llvm-as -f b.ll
$ opt -std-compile-opts -o a.bc -f b.bc
/Users/wendling/llvm/llvm.src/lib/Transforms/Scalar/InstructionCombining.cpp:1399: failed assertion
`DemandedElts != EltMask && (DemandedElts & ~EltMask) == 0 && "Invalid DemandedElts!"'
Abort trap

If it's more than 1 element in the vector, you get the failure reported in #1675 .