[SIL][PackageCMO] Allow optimizing [serialized_for_pkg] functions

[elsh]

Allow optimizing [serialized_for_pkg] functions during SIL inlining, generic/closure specialization, and devirtualization optimization passes.

SILFunction::canBeInlinedIntoCaller now exlicitly requires a caller's SerializedKind_t arg. isAnySerialized() is added as a convenience function that checks if [serialized] or [serialized_for_pkg].

Resolves rdar://128704752

[elsh]

@swift-ci test

[aschwaighofer]

We will also want to update the SwiftCompilerSources, they have instances of both usage of isSerialized and hasValidLinkageForFragileRef.

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyLoad.swift|284| if !function.isSerialized {
SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift|552| if parentFunction.isSerialized,                                                                                                            
SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift|554| !calleeFunction.isSerialized {
SwiftCompilerSources/Sources/SIL/Function.swift|123| public var isSerialized: Bool { bridged.isSerialized(

This code for example needs updating to take into account our canInlineInto matrix:

extension FullApplySite {                                                       
  var canInline: Bool {                                                         
    // Some checks which are implemented in C++                                 
    if !FullApplySite_canInline(bridged) {                                      
      return false                                                              
    }                                                                           
    // Cannot inline a non-inlinable function it an inlinable function.         
    if parentFunction.isSerialized,                                             
       let calleeFunction = referencedFunction,                                 
       !calleeFunction.isSerialized {                                           
      return false                                                              
    }        

[elsh]

@swift-ci test

[elsh]

@swift-ci test macOS

[nkcsgexi]

The functional part makes sense to me. Can we add tests to ensure that these optimization passes are actually active for serialized_for_pkg functions?

[aschwaighofer]

The added changes since my last review look good to me. We also need a change in SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift to take serializedForPackage into account:

     // Cannot inline a non-inlinable function it an inlinable function.         
    if parentFunction.isSerialized,                                             
       let calleeFunction = referencedFunction,                                 
       !calleeFunction.isSerialized {                                           
      return false                                                              
    } 

[elsh]

@swift-ci test

[elsh]

The functional part makes sense to me. Can we add tests to ensure that these optimization passes are actually active for serialized_for_pkg functions?

More tests including this are in the upcoming PR.