Provide overview documents

[thixotropist]

We need some overview documents to help ghidra users get a quick estimate of what a piece of extension code is doing.

What patterns are generated when?

• local optimization of similar scalar reads and writes, especially in initialization code
• vectorization of simple loops
• processing of vector instrinsic code
• vectorization of complex loops, especially iterating transforms over arrays of structures

Group vector instructions by complexity

• vector math and logical operations are easy
• vector gather, scatter, slideup, slidedown, segmented, strided, and indexed ops are more confusing

Gather concepts and glossary items

• element width, multipliers, segments, group, and all of the acronyms used in their definitions
• what rules does a compiler follow when deciding how to vectorize scalar code - exceptions, alignment, vector register pressure, memory latency, and branch prediction? How are these options passed to the compiler and to the runtime execution environment?

Modelling

• extract feature elements from binary code to help categorize semantics - how many reads and writes per loop, what are the likely type conversions present, is this an example of loop unrolling?
• what should the Ghidra decompiler window show when vector instructions are found?
• should Ghidra track the vector context registers?
• is there a vector or functional notation that captures vectorized code better than C?