[OSSACanonicalizeOwned] Dead-end extend base lifetime.

[nate-chandler]

Regardless of consumes of copies, if the original lexical value is not consumed on a dead-end path, it must remain live to that dead-end.

rdar://145226757

[meg-gupta]

@swift-ci build toolchain

[atrick]

Here are my review notes. Maybe they are useful for comments...

1. lexical-scope-extended liveness (lexical vars only):

1a. Separately compute the lexical lifetime of the original def.

This cannot include any consumes of copies. Otherwise, we would fail to extend the original lexical def:

 %copy = copy_value %def
 consume %copy
 apply foo()
 // need to extend the liveness of %def up to this point.
 unreachable

Note that none of the copied values are lexical, so they don't need to be extended to dead-end blocks.

1b. visit the lexical lifetime's availability boundary

Add the lexical boundary as uses to the current copy-extended liveness

Now we have an adjusted liveness that considers both the lexical lifetime and the copy-extended lifetime

===
2. complete liveness (always needed)

2a. create a temporary copy of copy-extended liveness

2b. demote and consumes within temporary liveness

If a lifetime-ending use is not on the liveness boundary, consider it a non-lifetime-ending use

Required by visitAvailabilityBoundary--the interior consumes will always be copied so they never kill availability.

2c. call visitAvailabilityBoundary on temporary liveness

Add instructions on the availability boundary to the original liveness, thereby extending it

Required to avoid inserting destroys within a borrow scope

 %c = copy_value %def
 %sb = store_borrow %c to ...
 // destroy_value %def - invalid
 unreachable

[nate-chandler]

@swift-ci please test

[nate-chandler]

@swift-ci please apple silicon benchmark

[nate-chandler]

@swift-ci please test source compatibility

[nate-chandler]

@swift-ci please build toolchain

[nate-chandler]

@swift-ci please test macos platform

[nate-chandler]

@swift-ci please test macos platform

[nate-chandler]

@swift-ci please test