* Update to rustfmt-preview.
* Run "cargo fmt --all" with rustfmt 0.4.1.
rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.
* Fix a long line that rustfmt 0.4.1 can't handle.
* Remove unneeded commas left behind by rustfmt.
* Add a pre-opt optimization to change constants into immediates.
This converts 'iadd' + 'iconst' into 'iadd_imm', and so on.
* Optimize away redundant `bint` instructions.
Cretonne has a concept of "Testable" values, which can be either boolean
or integer. When the an instruction needing a "Testable" value receives
the result of a `bint`, converting boolean to integer, eliminate the
`bint`, as it's redundant.
* Postopt: Optimize using CPU flags.
This introduces a post-legalization optimization pass which converts
compare+branch sequences to use flags values on CPUs which support it.
* Define a form of x86's `urm` that doesn't clobber FLAGS.
movzbl/movsbl/etc. don't clobber FLAGS; define a form of the `urm`
recipe that represents this.
* Implement a DCE pass.
This pass deletes instructions with no side effects and no results that
are used.
* Clarify ambiguity about "32-bit" and "64-bit" in comments.
* Add x86 encodings for icmp_imm.
* Add a testcase for postopt CPU flags optimization.
This covers the basic functionality of transforming compare+branch
sequences to use CPU flags.
* Pattern-match irsub_imm in preopt.
