[cast-opt] Refactor some code onto SILDynamicCast and delete dead code.

NFC.

Author: gottesmm

include/swift/SIL/DynamicCasts.h

@@ -448,6 +448,13 @@ struct SILDynamicCastInst {
     return t->getCanonicalType();
   }
 
+  Optional<SILType> getLoweredBridgedTargetObjectType() const {
+    CanType t = getBridgedTargetType();
+    if (!t)
+      return None;
+    return SILType::getPrimitiveObjectType(t);
+  }
+
   bool isConditional() const {
     switch (getKind()) {
     case SILDynamicCastKind::CheckedCastAddrBranchInst: {

lib/SILOptimizer/Utils/CastOptimizer.cpp

@@ -166,7 +166,6 @@ CastOptimizer::optimizeBridgedObjCToSwiftCast(SILDynamicCastInst dynamicCast) {
   SILInstruction *Inst = dynamicCast.getInstruction();
   bool isConditional = dynamicCast.isConditional();
   SILValue Dest = dynamicCast.getDest();
-  CanType BridgedTargetTy = dynamicCast.getBridgedTargetType();
   SILBasicBlock *SuccessBB = dynamicCast.getSuccessBlock();
   SILBasicBlock *FailureBB = dynamicCast.getFailureBlock();
   auto *F = Inst->getFunction();
@@ -186,9 +185,6 @@ CastOptimizer::optimizeBridgedObjCToSwiftCast(SILDynamicCastInst dynamicCast) {
              ParameterConvention::Direct_Guaranteed &&
          "Parameter should be @guaranteed");
 
-  CanType CanBridgedTy = BridgedTargetTy->getCanonicalType();
-  SILType silBridgedTy = SILType::getPrimitiveObjectType(CanBridgedTy);
-
   SILBuilderWithScope Builder(Inst, builderContext);
 
   // If this is a conditional cast:
@@ -215,6 +211,8 @@ CastOptimizer::optimizeBridgedObjCToSwiftCast(SILDynamicCastInst dynamicCast) {
     SILValue load =
         Builder.createLoad(Loc, src, LoadOwnershipQualifier::Unqualified);
 
+    SILType silBridgedTy = *dynamicCast.getLoweredBridgedTargetObjectType();
+
     // If type of the source and the expected ObjC type are equal, there is no
     // need to generate the conversion from ObjCTy to
     // _ObjectiveCBridgeable._ObjectiveCType.