Fix a bunch of places where operator-> was used directly on the return from dyn_cast.

Inspired by r331508, I did a grep and found these.

Mostly just change from dyn_cast to cast. Some cases also showed a dyn_cast result being converted to bool, so those I changed to isa.

llvm-svn: 331577
diff --git a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
index 37c55c4..e2a3efd 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
@@ -737,7 +737,7 @@
       unsigned PredicateExtraCost = 0;
       if (I != nullptr) {
         // Some predicates cost one or two extra instructions.
-        switch (dyn_cast<CmpInst>(I)->getPredicate()) {
+        switch (cast<CmpInst>(I)->getPredicate()) {
         case CmpInst::Predicate::ICMP_NE:
         case CmpInst::Predicate::ICMP_UGE:
         case CmpInst::Predicate::ICMP_ULE: