GlobalISel: Add a note about how we're being a bit loose with memory operands

The logic in r292461 is conservatively correct, but we should revisit
this later. Add a TODO so we don't forget.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292553 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed