Bugfix in BasicTTIImpl::getIntrinsicInstrCost()

[jonpa]

Summary

Fix for http://bugs.llvm.org/show_bug.cgi?id=32285

Originated in
https://reviews.llvm.org/D29540

[hfinkel]

I think this is fine, but please attach a regression test.

[jonpa]

commited as r297954.

I put the reduced test case under test/Analysis/CostModel/SystemZ, since it relates to cost functions and I have been working with it on SystemZ.

include/llvm/CodeGen/BasicTTIImpl.h

default: {
       if (VF > 1 && !RetTy->isVoidTy())
         RetTy = VectorType::get(RetTy, VF);
 
       // Compute the scalarization overhead based on Args for a vector
       // intrinsic. A vectorizer will pass a scalar RetTy and VF > 1, while
       // CostModel will pass a vector RetTy and VF is 1.
       unsigned ScalarizationCost = UINT_MAX;
       if (RetVF > 1 || VF > 1) {
-        ScalarizationCost = getScalarizationOverhead(RetTy, true, false);
+        ScalarizationCost = 0;
+        if (!RetTy->isVoidTy())
+          ScalarizationCost += getScalarizationOverhead(RetTy, true, false);
         ScalarizationCost += getOperandsScalarizationOverhead(Args, VF);
       }
 
       return static_cast<T *>(this)->
         getIntrinsicInstrCost(IID, RetTy, Types, FMF, ScalarizationCost);
     }
     case Intrinsic::masked_scatter: {
       assert (VF == 1 && "Can't vectorize types here.");