Implement Attribute Target MultiVersioning

GCC's attribute 'target', in addition to being an optimization hint,
also allows function multiversioning. We currently have the former
implemented, this is the latter's implementation.

This works by enabling functions with the same name/signature to coexist,
so that they can all be emitted. Multiversion state is stored in the
FunctionDecl itself, and SemaDecl manages the definitions.
Note that it ends up having to permit redefinition of functions so
that they can all be emitted. Additionally, all versions of the function
must be emitted, so this also manages that.

Note that this includes some additional rules that GCC does not, since
defining something as a MultiVersion function after a usage has been made illegal.

The only 'history rewriting' that happens is if a function is emitted before
it has been converted to a multiversion'ed function, at which point its name
needs to be changed.

Function templates and virtual functions are NOT yet supported (not supported
in GCC either).

Additionally, constructors/destructors are disallowed, but the former is 
planned.

llvm-svn: 322028

1 files changed, 12 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 22c4463b2c8..e63fa287064 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -324,6 +324,10 @@ private:
   /// is defined once we get to the end of the of the translation unit.
   std::vector<GlobalDecl> Aliases;
 
+  /// List of multiversion functions that have to be emitted.  Used to make sure
+  /// we properly emit the iFunc.
+  std::vector<GlobalDecl> MultiVersionFuncs;
+
   typedef llvm::StringMap<llvm::TrackingVH<llvm::Constant> > ReplacementsTy;
   ReplacementsTy Replacements;
 
@@ -1247,6 +1251,12 @@ private:
       llvm::AttributeList ExtraAttrs = llvm::AttributeList(),
       ForDefinition_t IsForDefinition = NotForDefinition);
 
+  llvm::Constant *GetOrCreateMultiVersionIFunc(GlobalDecl GD,
+                                               llvm::Type *DeclTy,
+                                               StringRef MangledName,
+                                               const FunctionDecl *FD);
+  void UpdateMultiVersionNames(GlobalDecl GD, const FunctionDecl *FD);
+
   llvm::Constant *GetOrCreateLLVMGlobal(StringRef MangledName,
                                         llvm::PointerType *PTy,
                                         const VarDecl *D,
@@ -1319,6 +1329,8 @@ private:
 
   void checkAliases();
 
+  void emitMultiVersionFunctions();
+
   /// Emit any vtables which we deferred and still have a use for.
   void EmitDeferredVTables();