This reverts commit b1eb70bf45.
The original PR (#85244) was reverted (#85836) due to rdar://165667449
This version fixes the aforementioned issue, and (potentially) improves overall
debug info retention by salvaging info in erase(instructionIncludingDebugUses:),
rather than inserting many explicit salvageDebugInfo calls throughout the code
to make the test cases pass.
Bridging: Make salvageDebugInfo a method of MutatingContext
This feels more consistent than making it a method of Instruction.
DebugInfo: Salvage from trivially dead instructions
This handles the case we were checking in constantFoldBuiltin, so we do not need to salvage debug info there any more.
Specifically, improved debug info retention in:
* tryReplaceRedundantInstructionPair,
* splitAggregateLoad,
* TempLValueElimination,
* Mem2Reg,
* ConstantFolding.
The changes to Mem2Reg allow debug info to be retained in the case tested by
self-nostorage.swift in -O builds, so we have just enabled -O in that file
instead of writing a new test for it.
We attempted to add a case to salvageDebugInfo for unchecked_enum_data, but it
caused crashes in Linux CI that we were not able to reproduce.
