Allow ToolChain to decide if Clang is not the right C compiler.

Removed comment in Driver::ShouldUseClangCompiler implying that there
was an opt-out ability at that point - there isn't.

Differential Revision: http://reviews.llvm.org/D10246

llvm-svn: 239608

clang/include/clang/Driver/ToolChain.h

@@ -164,7 +164,10 @@ public:
   }
 
   /// Choose a tool to use to handle the action \p JA.
-  Tool *SelectTool(const JobAction &JA) const;
+  ///
+  /// This can be overridden when a particular ToolChain needs to use
+  /// a C compiler other than Clang.
+  virtual Tool *SelectTool(const JobAction &JA) const;
 
   // Helper methods
 

clang/lib/Driver/Driver.cpp

@@ -2117,13 +2117,12 @@ const ToolChain &Driver::getToolChain(const ArgList &Args,
 }
 
 bool Driver::ShouldUseClangCompiler(const JobAction &JA) const {
-  // Check if user requested no clang, or clang doesn't understand this type (we
-  // only handle single inputs for now).
+  // Say "no" if there is not exactly one input of a type clang understands.
   if (JA.size() != 1 ||
       !types::isAcceptedByClang((*JA.begin())->getType()))
     return false;
 
-  // Otherwise make sure this is an action clang understands.
+  // And say "no" if this is not a kind of action clang understands.
   if (!isa<PreprocessJobAction>(JA) && !isa<PrecompileJobAction>(JA) &&
       !isa<CompileJobAction>(JA) && !isa<BackendJobAction>(JA))
     return false;