Implement cpu_dispatch/cpu_specific Multiversioning

As documented here: https://software.intel.com/en-us/node/682969 and
https://software.intel.com/en-us/node/523346. cpu_dispatch multiversioning
is an ICC feature that provides for function multiversioning.

This feature is implemented with two attributes: First, cpu_specific,
which specifies the individual function versions. Second, cpu_dispatch,
which specifies the location of the resolver function and the list of
resolvable functions.

This is valuable since it provides a mechanism where the resolver's TU
can be specified in one location, and the individual implementions
each in their own translation units.

The goal of this patch is to be source-compatible with ICC, so this
implementation diverges from the ICC implementation in a few ways:
1- Linux x86/64 only: This implementation uses ifuncs in order to
properly dispatch functions. This is is a valuable performance benefit
over the ICC implementation. A future patch will be provided to enable
this feature on Windows, but it will obviously more closely fit ICC's
implementation.
2- CPU Identification functions: ICC uses a set of custom functions to identify
the feature list of the host processor. This patch uses the cpu_supports
functionality in order to better align with 'target' multiversioning.
1- cpu_dispatch function def/decl: ICC's cpu_dispatch requires that the function
marked cpu_dispatch be an empty definition. This patch supports that as well,
however declarations are also permitted, since the linker will solve the
issue of multiple emissions.

Differential Revision: https://reviews.llvm.org/D47474

llvm-svn: 337552

1 files changed, 8 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index d2c7b327f98..ee64ed4f2ae 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -366,6 +366,13 @@ private:
   llvm::MapVector<GlobalDecl, StringRef> MangledDeclNames;
   llvm::StringMap<GlobalDecl, llvm::BumpPtrAllocator> Manglings;
 
+  // An ordered map of canonical GlobalDecls paired with the cpu-index for
+  // cpu-specific name manglings.
+  llvm::MapVector<std::pair<GlobalDecl, unsigned>, StringRef>
+      CPUSpecificMangledDeclNames;
+  llvm::StringMap<std::pair<GlobalDecl, unsigned>, llvm::BumpPtrAllocator>
+      CPUSpecificManglings;
+
   /// Global annotations.
   std::vector<llvm::Constant*> Annotations;
 
@@ -1283,7 +1290,6 @@ private:
 
   llvm::Constant *GetOrCreateMultiVersionIFunc(GlobalDecl GD,
                                                llvm::Type *DeclTy,
-                                               StringRef MangledName,
                                                const FunctionDecl *FD);
   void UpdateMultiVersionNames(GlobalDecl GD, const FunctionDecl *FD);
 
@@ -1307,6 +1313,7 @@ private:
   void EmitGlobalVarDefinition(const VarDecl *D, bool IsTentative = false);
   void EmitAliasDefinition(GlobalDecl GD);
   void emitIFuncDefinition(GlobalDecl GD);
+  void emitCPUDispatchDefinition(GlobalDecl GD);
   void EmitObjCPropertyImplementations(const ObjCImplementationDecl *D);
   void EmitObjCIvarInitializations(ObjCImplementationDecl *D);