[opaque pointer type] more gep API migrations

Adding nullptr to all the IRBuilder stuff because it's the first thing
that fails to build when testing without the back-compat functions, so
I'll keep having to re-add these locally for each chunk of migration I
do. Might as well check them in to save me the churn. Eventually I'll
have to migrate these too, but I'm going breadth-first.

llvm-svn: 232270
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index ae2e8a3..b6beb65 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -733,7 +733,8 @@
     case Instruction::GetElementPtr: {
       Value *Ptr = NewOps[0];
       ArrayRef<Value*> Idx = NewOps.slice(1);
-      GetElementPtrInst *GEP = GetElementPtrInst::Create(Ptr, Idx, "", I);
+      GetElementPtrInst *GEP = GetElementPtrInst::Create(
+          cast<GetElementPtrInst>(I)->getSourceElementType(), Ptr, Idx, "", I);
       GEP->setIsInBounds(cast<GetElementPtrInst>(I)->isInBounds());
       return GEP;
     }