[CallSite removal] Migrate ConstantFolding APIs and implementation to
`CallBase`.

Users have been updated. You can see how to update any out-of-tree
usages: pass `cast<CallBase>(CS.getInstruction())`.

llvm-svn: 353661
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index b7e6966..f10bc65 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -415,8 +415,8 @@
     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
       return C->isNullValue() || isa<UndefValue>(C);
 
-  if (CallSite CS = CallSite(I))
-    if (isMathLibCallNoop(CS, TLI))
+  if (auto *Call = dyn_cast<CallBase>(I))
+    if (isMathLibCallNoop(Call, TLI))
       return true;
 
   return false;