[6.2] Handle a special case of borrowed from instruction in CopyToBorrowOptimization #80971
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tbkka
approved these changes
Apr 21, 2025
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Cherry-pick from #80733. This change is needed for analyzing performance annotations due to the changes to the stdlib in #80956.
In CopyToBorrowOptimization, a copy_value with a guaranteed operand can be optimized away if all uses of copy_value can be replaced by the guaranteed operand and if the guaranteed operand's scope outlives the copy_value liveness.
For this, it uses lookThroughForwardingInstructions. Until now, for borrowed from instructions this utility returned its singleForwardedOperand which is a phi and not handled in isFullyContainedIn.
If the borrowed from instruction has a single enclosing value, we can return this instead enabling more optimizations if it turns out to be handled by isFullyContainedIn .