Re-apply "Fix linkage of 'static inline' Clang-imported definitions"

This re-applies commit r31763 with a change to the predicate we
use for determining the linkage of a definition. It turns out we
could have definitions with a Clang body that were still public,
so instead of checking for a Clang body just check if the Clang
declaration is externally visible or not.

Swift SVN r31777

include/swift/SIL/SILDeclRef.h

@@ -348,10 +348,14 @@ struct SILDeclRef {
   /// True if the referenced entity is some kind of thunk.
   bool isThunk() const;
 
-  /// True if the referenced entity is generated on behalf of the Clang
+  /// True if the referenced entity is emitted by Swift on behalf of the Clang
   /// importer.
   bool isClangImported() const;
 
+  /// True if the referenced entity is emitted by Clang on behalf of the Clang
+  /// importer.
+  bool isClangGenerated() const;
+
   bool isImplicit() const {
     if (hasDecl())
       return getDecl()->isImplicit();

include/swift/SIL/SILFunction.h

@@ -120,11 +120,13 @@ class SILFunction
   /// The linkage of the function.
   unsigned Linkage : NumSILLinkageBits;
 
-  /// This flags indicates if a function can be
-  /// eliminated by dead function elimination.
-  /// If it is unset, DFE will preserve the function
-  /// and make it public.
-  unsigned KeepAsPublic: 1;
+  /// This flag indicates if a function can be eliminated by dead function
+  /// elimination. If it is unset, DFE will preserve the function and make
+  /// it public.
+  unsigned KeepAsPublic : 1;
+
+  /// This flag indicates if a function has a body generated by Clang.
+  unsigned ForeignBody : 1;
 
   /// This is the number of uses of this SILFunction inside the SIL.
   /// It does not include references from debug scopes.
@@ -421,6 +423,10 @@ class SILFunction
   bool isKeepAsPublic() const { return KeepAsPublic; }
   void setKeepAsPublic(bool keep) { KeepAsPublic = keep; }
 
+  /// Get this function's foreign body attribute.
+  HasForeignBody_t hasForeignBody() const { return HasForeignBody_t(ForeignBody); }
+  void setForeignBody(HasForeignBody_t foreign) { ForeignBody = foreign; }
+
   /// Retrieve the generic parameter list containing the contextual archetypes
   /// of the function.
   ///

include/swift/SIL/SILLinkage.h

@@ -84,12 +84,18 @@ enum {
   NumSILLinkageBits = 3
 };
 
-/// Reslated to linkage: flag if a function or global variable is fragle.
+/// Related to linkage: flag if a function or global variable is fragile.
 enum IsFragile_t {
   IsNotFragile,
   IsFragile
 };
-
+
+/// True if we have an inline body generated by Clang.
+enum HasForeignBody_t {
+  DoesNotHaveForeignBody,
+  HasForeignBody
+};
+
 /// Strip external from public_external, hidden_external. Otherwise just return
 /// the linkage.
 inline SILLinkage stripExternalFromLinkage(SILLinkage linkage) {

lib/SIL/SILDeclRef.cpp

@@ -215,6 +215,9 @@ bool SILDeclRef::isClangImported() const {
   DeclContext *moduleContext = d->getDeclContext()->getModuleScopeContext();
 
   if (isa<ClangModuleUnit>(moduleContext)) {
+    if (isClangGenerated())
+      return true;
+
     if (isa<ConstructorDecl>(d) || isa<EnumElementDecl>(d))
       return true;
 
@@ -226,6 +229,19 @@ bool SILDeclRef::isClangImported() const {
   return false;
 }
 
+bool SILDeclRef::isClangGenerated() const {
+  if (!hasDecl())
+    return false;
+
+  auto clangNode = getDecl()->getClangNode().getAsDecl();
+  if (auto nd = dyn_cast_or_null<clang::NamedDecl>(clangNode)) {
+    if (!nd->isExternallyVisible())
+      return true;
+  }
+
+  return false;
+}
+
 SILLinkage SILDeclRef::getLinkage(ForDefinition_t forDefinition) const {
   // Anonymous functions have local linkage.
   if (auto closure = getAbstractClosureExpr())

lib/SIL/SILFunction.cpp

@@ -89,6 +89,7 @@ SILFunction::SILFunction(SILModule &Module, SILLinkage Linkage,
     InlineStrategy(inlineStrategy),
     Linkage(unsigned(Linkage)),
     KeepAsPublic(false),
+    ForeignBody(false),
     EK(E) {
   if (InsertBefore)
     Module.functions.insert(SILModule::iterator(InsertBefore), this);

lib/SIL/SILModule.cpp

@@ -359,10 +359,14 @@ SILFunction *SILModule::getOrCreateFunction(SILLocation loc,
     F->setDebugScope(new (*this) SILDebugScope(loc, *F));
 
   F->setGlobalInit(constant.isGlobal());
-  if (constant.hasDecl())
+  if (constant.hasDecl()) {
+    if (constant.isForeign && constant.isClangGenerated())
+      F->setForeignBody(HasForeignBody);
+
     if (auto SemanticsA =
         constant.getDecl()->getAttrs().getAttribute<SemanticsAttr>())
       F->setSemanticsAttr(SemanticsA->Value);
+  }
 
   F->setDeclContext(constant.hasDecl() ? constant.getDecl() : nullptr);
 

lib/SIL/Verifier.cpp

@@ -2947,16 +2947,21 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
     verifySILFunctionType(FTy);
 
     if (F->isExternalDeclaration()) {
+      if (F->hasForeignBody())
+        return;
+
       assert(F->isAvailableExternally() &&
              "external declaration of internal SILFunction not allowed");
       assert(!hasSharedVisibility(F->getLinkage()) &&
-             "external declarations of SILFunctions with shared visiblity is not "
+             "external declarations of SILFunctions with shared visibility is not "
              "allowed");
       // If F is an external declaration, there is nothing further to do,
       // return.
       return;
     }
 
+    assert(!F->hasForeignBody());
+
     // Make sure that our SILFunction only has context generic params if our
     // SILFunctionType is non-polymorphic.
     if (F->getContextGenericParams()) {

test/IRGen/c_globals.swift

@@ -6,7 +6,7 @@ import c_layout
 func blackHole<T>(t: T) { }
 
 // CHECK: @staticFloat = internal global float 1.700000e+01, align 4
-// CHECK: define {{.*}}void @doubleTrouble() [[CLANG_FUNC_ATTR:#[0-9]+]] {
+// CHECK: define internal void @doubleTrouble() [[CLANG_FUNC_ATTR:#[0-9]+]] {
 
 public func testStaticGlobal() {
   blackHole(c_layout.staticFloat)

test/SILGen/Inputs/usr/include/Ansible.h

@@ -4,8 +4,14 @@
 - (Ansible*)initWithBellsOn:(id)theBells;
 @end
 
-Ansible *NSAnse(Ansible *x) {
+static Ansible *NSAnse(Ansible *x) {
+  return x;
+}
+
+Ansible *NSAnseExternal(Ansible *x) {
   return x;
 }
 
 void hasNoPrototype();
+
+static void staticForwardDeclaration(void);