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.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@322028 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 0 deletions

diff --git a/include/clang/Basic/TargetInfo.h b/include/clang/Basic/TargetInfo.h
index 6ba5877911..fad923c272 100644
--- a/include/clang/Basic/TargetInfo.h
+++ b/include/clang/Basic/TargetInfo.h
@@ -920,10 +920,20 @@ public:
     return false;
   }
 
+  /// \brief Identify whether this taret supports multiversioning of functions,
+  /// which requires support for cpu_supports and cpu_is functionality.
+  virtual bool supportsMultiVersioning() const { return false; }
+
   // \brief Validate the contents of the __builtin_cpu_supports(const char*)
   // argument.
   virtual bool validateCpuSupports(StringRef Name) const { return false; }
 
+  // \brief Return the target-specific priority for features/cpus/vendors so
+  // that they can be properly sorted for checking.
+  virtual unsigned multiVersionSortPriority(StringRef Name) const {
+    return 0;
+  }
+
   // \brief Validate the contents of the __builtin_cpu_is(const char*)
   // argument.
   virtual bool validateCpuIs(StringRef Name) const { return false; }