Add a function index

This radically simplifies the representation of function sets when
analyzing the entire module's call graph at once.

Author: atrick

include/swift/SIL/SILFunction.h

@@ -224,6 +224,10 @@ class SILFunction
   /// For details see BasicBlockBitfield::bitfieldID;
   unsigned currentBitfieldID = 1;
 
+  /// Unique identifier for vector indexing and deterministic sorting.
+  /// May be reused when zombie functions are recovered.
+  unsigned index;
+
   /// The function's set of semantics attributes.
   ///
   /// TODO: Why is this using a std::string? Why don't we use uniqued
@@ -446,6 +450,8 @@ class SILFunction
     return SILFunctionConventions(fnType, getModule());
   }
 
+  unsigned getIndex() const { return index; }
+
   SILProfiler *getProfiler() const { return Profiler; }
 
   SILFunction *getDynamicallyReplacedFunction() const {

include/swift/SIL/SILModule.h

@@ -345,6 +345,10 @@ class SILModule {
   /// The options passed into this SILModule.
   const SILOptions &Options;
 
+  /// The number of functions created in this module, which will be the index of
+  /// the next function.
+  unsigned nextFunctionIndex = 0;
+
   /// Set if the SILModule was serialized already. It is used
   /// to ensure that the module is serialized only once.
   bool serialized;
@@ -449,6 +453,12 @@ class SILModule {
   /// Called after an instruction is moved from one function to another.
   void notifyMovedInstruction(SILInstruction *inst, SILFunction *fromFunction);
 
+  unsigned getNewFunctionIndex() { return nextFunctionIndex++; }
+
+  // This may be larger that the number of live functions in the 'functions'
+  // linked list because it includes the indices of zombie functions.
+  unsigned getNumFunctionIndices() const { return nextFunctionIndex; }
+
   /// Set a serialization action.
   void setSerializeSILAction(ActionCallback SerializeSILAction);
   ActionCallback getSerializeSILAction() const;

lib/SIL/IR/SILFunction.cpp

@@ -150,8 +150,9 @@ SILFunction::SILFunction(SILModule &Module, SILLinkage Linkage, StringRef Name,
                          IsDynamicallyReplaceable_t isDynamic,
                          IsExactSelfClass_t isExactSelfClass,
                          IsDistributed_t isDistributed)
-    : SwiftObjectHeader(functionMetatype),
-      Module(Module), Availability(AvailabilityContext::alwaysAvailable())  {
+    : SwiftObjectHeader(functionMetatype), Module(Module),
+      index(Module.getNewFunctionIndex()),
+      Availability(AvailabilityContext::alwaysAvailable()) {
   init(Linkage, Name, LoweredType, genericEnv, Loc, isBareSILFunction, isTrans,
        isSerialized, entryCount, isThunk, classSubclassScope, inlineStrategy,
        E, DebugScope, isDynamic, isExactSelfClass, isDistributed);