[dev.ssa] cmd/internal/ssa: Handle more instructions + some cleanup
Add & as an input op. Add several output ops (loads & stores, TESTB,
LEAQglobal, branches, memcopy)
Some other small things:
- Add exprAddr to builder to generate addresses of expressions. Use it in
various places that had ad-hoc code.
- Separate out nil & bounds check generation to separate functions.
- Add explicit FP and SP ops so we dont need specialized *FP and *SP opcodes.
- Fix fallthrough at end of functions with no return values.
- rematerialization of more opcodes.
Change-Id: I781decfcef9770fb15f0cd6b061547f7824a2d5e
Reviewed-on: https://go-review.googlesource.com/10213 Reviewed-by: Alan Donovan <adonovan@google.com>