cmd/compile: introduce separate memory op combining pass

Memory op combining is currently done using arch-specific rewrite rules.
Instead, do them as a arch-independent rewrite pass. This ensures that
all architectures (with unaligned loads & stores) get equal treatment.

This removes a lot of rewrite rules.

The new pass is a bit more comprehensive. It handles things like out-of-order
writes and is careful not to apply partial optimizations that then block
further optimizations.

Change-Id: I780ff3bb052475cd725a923309616882d25b8d9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/478475
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
17 files changed
tree: a75ad1fde9937d7c0a15b42479b610333fb65c4a
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. codereview.cfg
  11. CONTRIBUTING.md
  12. go.env
  13. LICENSE
  14. PATENTS
  15. README.md
  16. SECURITY.md
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