[IR] Use CallBase to reduce code duplication. NFC

[craig.topper]

Summary

Noticed in the asm-goto patch. Callbr needs to go here too. One cast and call is better than 3.

[chandlerc]

LGTM

llvm/trunk/lib/IR/Instruction.cpp

bool Instruction::mayReadFromMemory() const {
   case Instruction::Load:
   case Instruction::Fence: // FIXME: refine definition of mayReadFromMemory
   case Instruction::AtomicCmpXchg:
   case Instruction::AtomicRMW:
   case Instruction::CatchPad:
   case Instruction::CatchRet:
     return true;
   case Instruction::Call:
-    return !cast<CallInst>(this)->doesNotAccessMemory();
   case Instruction::Invoke:
-    return !cast<InvokeInst>(this)->doesNotAccessMemory();
+    return !cast<CallBase>(this)->doesNotAccessMemory();
   case Instruction::Store:
     return !cast<StoreInst>(this)->isUnordered();
   }
 }
 
 bool Instruction::mayWriteToMemory() const {
   switch (getOpcode()) {
   default: return false;
   case Instruction::Fence: // FIXME: refine definition of mayWriteToMemory
   case Instruction::Store:
   case Instruction::VAArg:
   case Instruction::AtomicCmpXchg:
   case Instruction::AtomicRMW:
   case Instruction::CatchPad:
   case Instruction::CatchRet:
     return true;
   case Instruction::Call:
-    return !cast<CallInst>(this)->onlyReadsMemory();
   case Instruction::Invoke:
-    return !cast<InvokeInst>(this)->onlyReadsMemory();
+    return !cast<CallBase>(this)->onlyReadsMemory();
   case Instruction::Load:
     return !cast<LoadInst>(this)->isUnordered();
   }
 }
 
 bool Instruction::isAtomic() const {
   switch (getOpcode()) {
   default: