[semantic-arc-opts] Use the LiveRange abstraction to find destroys instead of iterating over direct uses so we handle forwarding uses.

[gottesmm]

Previously, we were incorrectly handling these test cases since we weren't
properly finding destroys through forwarding instructions. I fixed that in a
previous commit by changing the code here to only support load [copy] without
forwarding instructions.

In this commit, I change the code to instead use the LiveRange abstraction. The
LiveRange abstraction already knows how to find destroys through forwarding
instructions and has this destroy array already computed for us!

So we get better runtime performance of code (due to the better opt) and better
compile time (since we aren't computing the destroy list twice)!

rdar://58289320

[gottesmm]

@swift-ci test

[gottesmm]

@swift-ci benchmark

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 2b09547

[gottesmm]

@swift-ci test os x platform

[swift-ci]

Performance: -O

Improvement	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	4876	4440	-8.9%	1.10x (?)

Code size: -O

Performance: -Osize

Improvement	OLD	NEW	DELTA	RATIO
FlattenListLoop	2756	2572	-6.7%	1.07x (?)

Code size: -Osize

Performance: -Onone

Improvement	OLD	NEW	DELTA	RATIO
DataAppendDataSmallToSmall	3200	2800	-12.5%	1.14x (?)

Code size: -swiftlibs

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac mini
  Model Identifier: Macmini8,1
  Processor Name: Intel Core i7
  Processor Speed: 3.2 GHz
  Number of Processors: 1
  Total Number of Cores: 6
  L2 Cache (per Core): 256 KB
  L3 Cache: 12 MB
  Memory: 64 GB

[gottesmm]

No regressions, good. I figured we wouldn't see much since we hadn't hit this bug yet.

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 2b09547

[gottesmm]

@swift-ci test linux platform

[gottesmm]

@swift-ci test windows platform