[msan] A no-op implementation of VarArg handling.

This stuff is used on platforms where MSan does not have a proper VarArg
implementation (anything other than x86_64 at the moment).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182375 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -74,6 +74,7 @@
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/ADT/ValueMap.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Function.h"
@@ -1963,9 +1964,29 @@ struct VarArgAMD64Helper : public VarArgHelper {
   }
 };
 
-VarArgHelper* CreateVarArgHelper(Function &Func, MemorySanitizer &Msan,
+/// \brief A no-op implementation of VarArgHelper.
+struct VarArgNoOpHelper : public VarArgHelper {
+  VarArgNoOpHelper(Function &F, MemorySanitizer &MS,
+                   MemorySanitizerVisitor &MSV) {}
+
+  void visitCallSite(CallSite &CS, IRBuilder<> &IRB) {}
+
+  void visitVAStartInst(VAStartInst &I) {}
+
+  void visitVACopyInst(VACopyInst &I) {}
+
+  void finalizeInstrumentation() {}
+};
+
+VarArgHelper *CreateVarArgHelper(Function &Func, MemorySanitizer &Msan,
                                  MemorySanitizerVisitor &Visitor) {
-  return new VarArgAMD64Helper(Func, Msan, Visitor);
+  // VarArg handling is only implemented on AMD64. False positives are possible
+  // on other platforms.
+  llvm::Triple TargetTriple(Func.getParent()->getTargetTriple());
+  if (TargetTriple.getArch() == llvm::Triple::x86_64)
+    return new VarArgAMD64Helper(Func, Msan, Visitor);
+  else
+    return new VarArgNoOpHelper(Func, Msan, Visitor);
 }
 
 }  // namespace