Optimizer: add a new destroy-hoisting optimization #78059
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eeckstein
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Just don't store the begin instruction. This led to problem if the "begin" was not actually an instruction but a block argument. Using the first instruction of that block is not correct in case the range ends immediately at the first instruction, e.g. ``` bb0(%0 : @owned $C): destroy_value %0 ```
This avoids the need for checking if a value is a `move_value`, `begin_borrow` or function argument to get the is-lexical information.
and not just for `CollectionLikeSequence`. To support stdlib's lazy map and filter sequences.
It hoists `destroy_value` instructions without shrinking an object's lifetime. This is done if it can be proved that another copy of a value (either in an SSA value or in memory) keeps the referenced object(s) alive until the original position of the `destroy_value`. ``` %1 = copy_value %0 ... last_use_of %0 // other instructions destroy_value %0 // %1 is still alive here ``` -> ``` %1 = copy_value %0 ... last_use_of %0 destroy_value %0 // other instructions ``` The benefit of this optimization is that it can enable copy-propagation by moving destroys above deinit barries and access scopes.
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It hoists
destroy_valueinstructions without shrinking an object's lifetime.This is done if it can be proved that another copy of a value (either in an SSA value or in memory) keeps the referenced object(s) alive until the original position of the
destroy_value.->
The benefit of this optimization is that it can enable copy-propagation by moving destroys above deinit barries and access scopes.
This is part of fixing benchmark regressions when enabling OSSA modules.
rdar://139773406