Rewrite the pipeline overview to be more focused on the structure and
flexibility as well as highlight the increased usefulness of
MachineVerifier and increased testability resulting from the smaller
incremental passes approach.
The diagrams are lifted from the slides for the LLVMDev 2019 talk
'Generating Optimized Code with GlobalISel' and adapted to be readable on
the white background used in the docs.
I think somewhere in this paragraph we should mention what gMIR stands for (just so we don't introduce unexplained acronyms - even if all the details are just a click away).
Perhaps also a sentence or two explaining the exact relationship between MIR and gMIR would make the rest of the text easier to read (I'm thinking especially around lines 51-52) .