SIL: simplify the SILNode getParent functions.

A small cleanup, NFC.

Author: eeckstein

include/swift/SIL/SILInstruction.h

@@ -405,8 +405,7 @@ class SILInstruction
     return SILInstructionKind(SILNode::getKind());
   }
 
-  const SILBasicBlock *getParent() const { return ParentBB; }
-  SILBasicBlock *getParent() { return ParentBB; }
+  SILBasicBlock *getParent() const { return ParentBB; }
 
   SILFunction *getFunction();
   const SILFunction *getFunction() const;

lib/SIL/IR/SILValue.cpp

@@ -99,32 +99,25 @@ ValueBase::getDefiningInstructionResult() {
 }
 
 SILBasicBlock *SILNode::getParentBlock() const {
-  auto *CanonicalNode =
-      const_cast<SILNode *>(this)->getRepresentativeSILNodeInObject();
-  if (auto *Inst = dyn_cast<SILInstruction>(CanonicalNode))
+  if (auto *Inst = dyn_cast<SILInstruction>(this))
     return Inst->getParent();
-  if (auto *Arg = dyn_cast<SILArgument>(CanonicalNode))
+  if (auto *Arg = dyn_cast<SILArgument>(this))
     return Arg->getParent();
+  if (auto *MVR = dyn_cast<MultipleValueInstructionResult>(this)) {
+    return MVR->getParent()->getParent();
+  }
   return nullptr;
 }
 
 SILFunction *SILNode::getFunction() const {
-  auto *CanonicalNode =
-      const_cast<SILNode *>(this)->getRepresentativeSILNodeInObject();
-  if (auto *Inst = dyn_cast<SILInstruction>(CanonicalNode))
-    return Inst->getFunction();
-  if (auto *Arg = dyn_cast<SILArgument>(CanonicalNode))
-    return Arg->getFunction();
+  if (auto *parentBlock = getParentBlock())
+    return parentBlock->getParent();
   return nullptr;
 }
 
 SILModule *SILNode::getModule() const {
-  auto *CanonicalNode =
-      const_cast<SILNode *>(this)->getRepresentativeSILNodeInObject();
-  if (auto *Inst = dyn_cast<SILInstruction>(CanonicalNode))
-    return &Inst->getModule();
-  if (auto *Arg = dyn_cast<SILArgument>(CanonicalNode))
-    return &Arg->getModule();
+  if (SILFunction *func = getFunction())
+    return &func->getModule();
   return nullptr;
 }