Add accessors for linkage. (#27)

* Add accessors for linkage.

Obsolete linkage is intentionally left out for obvious reasons.

* Split linkage into its own file

Author: CodaFi

Sources/LLVM/Function.swift

@@ -107,6 +107,12 @@ public class Function: IRValue {
     LLVMDeleteFunction(llvm)
   }
 
+  /// Retrieves the linkage information for this function.
+  public var linkage: Linkage {
+    get { return Linkage(llvm: LLVMGetLinkage(asLLVM())) }
+    set { LLVMSetLinkage(asLLVM(), newValue.llvm) }
+  }
+
   /// Retrieves the underlying LLVM value object.
   public func asLLVM() -> LLVMValueRef {
     return llvm

Sources/LLVM/Global.swift

@@ -33,6 +33,12 @@ public struct Global: IRValue {
     set { LLVMSetThreadLocal(asLLVM(), newValue.llvm) }
   }
 
+  /// Retrieves the linkage information for this global value.
+  public var linkage: Linkage {
+    get { return Linkage(llvm: LLVMGetLinkage(asLLVM())) }
+    set { LLVMSetLinkage(asLLVM(), newValue.llvm) }
+  }
+
   /// Deletes the global variable from its containing module.
   /// - note: This does not remove references to this global from the
   ///         module. Ensure you have removed all insructions that reference

Sources/LLVM/Linkage.swift

@@ -0,0 +1,137 @@
+import cllvm
+
+/// `Linkage` enumerates the supported kinds of linkage for global values.  All
+/// global variables and functions have a linkage.
+public enum Linkage {
+  /// Externally visible function.  This is the default linkage.
+  ///
+  /// If none of the other linkages are specified, the global is externally
+  /// visible, meaning that it participates in linkage and can be used to
+  /// resolve external symbol references.
+  case external
+  /// Available for inspection, not emission.
+  ///
+  /// Globals with "available_externally" linkage are never emitted into the
+  /// object file corresponding to the LLVM module. From the linker’s
+  /// perspective, an available_externally global is equivalent to an external
+  /// declaration. They exist to allow inlining and other optimizations to take
+  /// place given knowledge of the definition of the global, which is known to
+  /// be somewhere outside the module. Globals with available_externally linkage
+  /// are allowed to be discarded at will, and allow inlining and other
+  /// optimizations. This linkage type is only allowed on definitions, not
+  /// declarations.
+  case availableExternally
+  /// Keep one copy of function when linking.
+  ///
+  /// Globals with "linkonce" linkage are merged with other globals of the same
+  /// name when linkage occurs. This can be used to implement some forms of
+  /// inline functions, templates, or other code which must be generated in each
+  /// translation unit that uses it, but where the body may be overridden with a
+  /// more definitive definition later. Unreferenced linkonce globals are
+  /// allowed to be discarded. Note that linkonce linkage does not actually
+  /// allow the optimizer to inline the body of this function into callers
+  /// because it doesn’t know if this definition of the function is the
+  /// definitive definition within the program or whether it will be overridden
+  /// by a stronger definition.
+  case linkOnceAny
+  /// Keep one copy of function when linking but enable inlining and
+  /// other optimizations.
+  ///
+  /// Some languages allow differing globals to be merged, such as two functions
+  /// with different semantics. Other languages, such as C++, ensure that only
+  /// equivalent globals are ever merged (the "one definition rule" — "ODR").
+  /// Such languages can use the linkonce_odr and weak_odr linkage types to
+  /// indicate that the global will only be merged with equivalent globals.
+  /// These linkage types are otherwise the same as their non-odr versions.
+  case linkOnceODR
+  /// Keep one copy of function when linking (weak).
+  ///
+  /// "weak" linkage has the same merging semantics as linkonce linkage, except
+  /// that unreferenced globals with weak linkage may not be discarded. This is
+  /// used for globals that are declared "weak" in C source code.
+  case weakAny
+  /// Keep one copy of function when linking but apply "One Definition Rule"
+  /// semantics.
+  ///
+  /// Some languages allow differing globals to be merged, such as two functions
+  /// with different semantics. Other languages, such as C++, ensure that only
+  /// equivalent globals are ever merged (the "one definition rule" — "ODR").
+  /// Such languages can use the linkonce_odr and weak_odr linkage types to
+  /// indicate that the global will only be merged with equivalent globals.
+  /// These linkage types are otherwise the same as their non-odr versions.
+  case weakODR
+  /// Special purpose, only applies to global arrays.
+  ///
+  /// "appending" linkage may only be applied to global variables of pointer to
+  /// array type. When two global variables with appending linkage are linked
+  /// together, the two global arrays are appended together. This is the LLVM,
+  /// typesafe, equivalent of having the system linker append together
+  /// "sections" with identical names when .o files are linked.
+  ///
+  /// Unfortunately this doesn’t correspond to any feature in .o files, so it
+  /// can only be used for variables like llvm.global_ctors which llvm
+  /// interprets specially.
+  case appending
+  /// Rename collisions when linking (static functions).
+  ///
+  /// Similar to private, but the value shows as a local symbol
+  /// (`STB_LOCAL` in the case of ELF) in the object file. This corresponds to
+  /// the notion of the `static` keyword in C.
+  case `internal`
+  /// Like `.internal`, but omit from symbol table.
+  ///
+  /// Global values with "private" linkage are only directly accessible by
+  /// objects in the current module. In particular, linking code into a module
+  /// with an private global value may cause the private to be renamed as
+  /// necessary to avoid collisions. Because the symbol is private to the
+  /// module, all references can be updated. This doesn’t show up in any symbol
+  /// table in the object file.
+  case `private`
+  /// Keep one copy of the function when linking, but apply ELF semantics.
+  ///
+  /// The semantics of this linkage follow the ELF object file model: the symbol
+  /// is weak until linked, if not linked, the symbol becomes null instead of
+  /// being an undefined reference.
+  case externalWeak
+  /// Tentative definitions.
+  ///
+  /// "common" linkage is most similar to "weak" linkage, but they are used for
+  /// tentative definitions in C, such as "int X;" at global scope. Symbols with
+  /// "common" linkage are merged in the same way as weak symbols, and they may
+  /// not be deleted if unreferenced. common symbols may not have an explicit
+  /// section, must have a zero initializer, and may not be marked ‘constant‘.
+  /// Functions and aliases may not have common linkage.
+  case common
+
+  private static let linkageMapping: [Linkage: LLVMLinkage] = [
+    .external: LLVMExternalLinkage,
+    .availableExternally: LLVMAvailableExternallyLinkage,
+    .linkOnceAny: LLVMLinkOnceAnyLinkage, .linkOnceODR: LLVMLinkOnceODRLinkage,
+    .weakAny: LLVMWeakAnyLinkage, .weakODR: LLVMWeakODRLinkage,
+    .appending: LLVMAppendingLinkage, .`internal`: LLVMInternalLinkage,
+    .`private`: LLVMPrivateLinkage, .externalWeak: LLVMExternalWeakLinkage,
+    .common: LLVMCommonLinkage,
+  ]
+
+  internal init(llvm: LLVMLinkage) {
+    switch llvm {
+    case LLVMExternalLinkage: self = .external
+    case LLVMAvailableExternallyLinkage: self = .availableExternally
+    case LLVMLinkOnceAnyLinkage: self = .linkOnceAny
+    case LLVMLinkOnceODRLinkage: self = .linkOnceODR
+    case LLVMWeakAnyLinkage: self = .weakAny
+    case LLVMWeakODRLinkage: self = .weakODR
+    case LLVMAppendingLinkage: self = .appending
+    case LLVMInternalLinkage: self = .internal
+    case LLVMPrivateLinkage: self = .private
+    case LLVMExternalWeakLinkage: self = .externalWeak
+    case LLVMCommonLinkage: self = .common
+    default: fatalError("unknown linkage type \(llvm)")
+    }
+  }
+
+  /// Retrieves the corresponding `LLVMLinkage`.
+  public var llvm: LLVMLinkage {
+    return Linkage.linkageMapping[self]!
+  }
+}