Set calling convention for varargs

[hiraditya]

Summary

Varargs only follow C calling conventions.

Unfortunately, I do not have a test case for this. I just saw this while reading the code.

[efriedma]

What branch is this patch against? Trunk doesn't have a file named MergeSimilarFunctions.cpp.

[hiraditya]

This is not in trunk I guess, I borrowed this pass from: https://reviews.llvm.org/D22051

lib/Transforms/IPO/MergeSimilarFunctions.cpp

static Function *cloneAndAddArgument(Function *F1, ValueToValueMapTy &VMap) {
   Function *NewF = Function::Create(FTy, F1->getLinkage(),
                                     F1->getName()+MERGED_SUFFIX);
 
   insertFunctionAfter(NewF, F1);
 
   if (F1->hasSection())
     NewF->setSection(F1->getSection());
 
+  if (F1->getFunctionType()->isVarArg())
+    NewF->setCallingConv(CallingConv::C);
+  else
     NewF->setCallingConv(CallingConv::Fast);
 
   Function::arg_iterator DestI = NewF->arg_begin();
   for (auto &Arg : F1->args()) {
     Argument *DestIn = &*DestI;
     DestIn->setName(Arg.getName()); // Copy the name over...
     VMap[&Arg] = DestIn;            // Add mapping to VMap
     ++DestI;
   }