Min-Yih Hsu 9a8f2ed642 [SILOptimizer][DebugInfo] Preliminary support for DIExpression in SROA and Mem2Reg ...

SROA and Mem2Reg now can leverage DIExpression -- op_fragment, more
specifically -- to generate correct debug info for optimized SIL. Some
important highlights:
 - The new swift::salvageDebugInfo, similar to llvm::salvageDebugInfo,
   tries to restore / transfer debug info from a deleted instruction.
   Currently I only implemented this for store instruction whose
   destination is an alloc_stack value.
 - Since we now have source-variable-specific SIL location inside a
   `debug_value` instruction (and its friends), this patch teaches
   SILCloner and SILInliner to remap the debug scope there in addition
   to debug scope of the instruction.
 - DCE now does not remove `debug_value` instruction whose associating
   with a function argument SSA value that is not used elsewhere. Since
   that SSA value will not disappear so we should keep the debug info.

2021-08-05 17:27:45 -07:00

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