SILGen/IRGen: Delegate decision to skip @_silgen_name functions to TBDGenVisitor.

This allows SILGen for `#_hasSymbol` conditions to visit them and emit a declaration of the function appropriately.

Author: tshortli

include/swift/IRGen/IRSymbolVisitor.h

@@ -58,7 +58,8 @@ class IRSymbolVisitor {
                     const IRSymbolVisitorContext &ctx);
 
   /// Override to prepare for enumeration of the symbols for a specific decl.
-  virtual void willVisitDecl(Decl *D) {}
+  /// Return \c true to proceed with visiting the decl or \c false to skip it.
+  virtual bool willVisitDecl(Decl *D) { return true; }
 
   /// Override to clean up after enumeration of the symbols for a specific decl.
   virtual void didVisitDecl(Decl *D) {}

include/swift/SIL/SILSymbolVisitor.h

@@ -76,7 +76,8 @@ class SILSymbolVisitor {
                     const SILSymbolVisitorContext &ctx);
 
   /// Override to prepare for enumeration of the symbols for a specific decl.
-  virtual void willVisitDecl(Decl *D) {}
+  /// Return \c true to proceed with visiting the decl or \c false to skip it.
+  virtual bool willVisitDecl(Decl *D) { return true; }
 
   /// Override to clean up after enumeration of the symbols for a specific decl.
   virtual void didVisitDecl(Decl *D) {}

lib/IRGen/IRSymbolVisitor.cpp

@@ -72,8 +72,8 @@ class IRSymbolVisitorImpl : public SILSymbolVisitor {
       : Visitor{Visitor}, Ctx{Ctx},
         PublicSymbolsOnly{Ctx.getSILCtx().getOpts().PublicSymbolsOnly} {}
 
-  void willVisitDecl(Decl *D) override {
-    Visitor.willVisitDecl(D);
+  bool willVisitDecl(Decl *D) override {
+    return Visitor.willVisitDecl(D);
   }
 
   void didVisitDecl(Decl *D) override {

lib/IRGen/TBDGen.cpp

@@ -400,8 +400,15 @@ void TBDGenVisitor::addSymbol(StringRef name, SymbolSource source,
   }
 }
 
-void TBDGenVisitor::willVisitDecl(Decl *D) {
+bool TBDGenVisitor::willVisitDecl(Decl *D) {
+  // A @_silgen_name("...") function without a body only exists to
+  // forward-declare a symbol from another library.
+  if (auto AFD = dyn_cast<AbstractFunctionDecl>(D))
+    if (!AFD->hasBody() && AFD->getAttrs().hasAttribute<SILGenNameAttr>())
+      return false;
+
   DeclStack.push_back(D);
+  return true;
 }
 
 void TBDGenVisitor::didVisitDecl(Decl *D) {

lib/IRGen/TBDGenVisitor.h

@@ -139,7 +139,7 @@ class TBDGenVisitor : public IRSymbolVisitor {
 
   // --- IRSymbolVisitor ---
 
-  void willVisitDecl(Decl *D) override;
+  bool willVisitDecl(Decl *D) override;
   void didVisitDecl(Decl *D) override;
 
   void addFunction(SILDeclRef declRef) override;

lib/SIL/IR/SILSymbolVisitor.cpp

@@ -362,7 +362,8 @@ class SILSymbolVisitorImpl : public ASTVisitor<SILSymbolVisitorImpl> {
       : Visitor{Visitor}, Ctx{Ctx} {}
 
   void visit(Decl *D) {
-    Visitor.willVisitDecl(D);
+    if (!Visitor.willVisitDecl(D))
+      return;
     ASTVisitor::visit(D);
     Visitor.didVisitDecl(D);
   }
@@ -408,12 +409,6 @@ class SILSymbolVisitorImpl : public ASTVisitor<SILSymbolVisitorImpl> {
   }
 
   void visitAbstractFunctionDecl(AbstractFunctionDecl *AFD) {
-    // A @_silgen_name("...") function without a body only exists to
-    // forward-declare a symbol from another library.
-    if (!AFD->hasBody() && AFD->getAttrs().hasAttribute<SILGenNameAttr>()) {
-      return;
-    }
-
     // Add exported prespecialized symbols.
     for (auto *attr : AFD->getAttrs().getAttributes<SpecializeAttr>()) {
       if (!attr->isExported())

test/SILGen/has_symbol.swift

@@ -41,7 +41,7 @@ func testGlobalFunctions() {
 
 // --- forwardDeclaredFunc() ---
 // CHECK: sil hidden_external @$s17has_symbol_helper19forwardDeclaredFuncyyFTwS : $@convention(thin) () -> Builtin.Int1
-// FIXME: missing forward declared function
+// CHECK: sil @forward_declared_func : $@convention(thin) () -> ()
 
 
 // CHECK: sil hidden [ossa] @$s4test0A4VarsyyF : $@convention(thin) () -> ()