[LVI] Drop bitcast handling (NFCI)

The code only works on integer casts, and the only bitcasts
involving integers are trivial. The code as previously written
would try to handle things like float to integer bitcasts by
fetching a ConstantRange of a float value, which is an ill-defined
operation.

Author: nikic

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -903,19 +903,13 @@ LazyValueInfoImpl::getRangeFor(Value *V, Instruction *CxtI, BasicBlock *BB) {
 
 std::optional<ValueLatticeElement>
 LazyValueInfoImpl::solveBlockValueCast(CastInst *CI, BasicBlock *BB) {
-  // Without knowing how wide the input is, we can't analyze it in any useful
-  // way.
-  if (!CI->getOperand(0)->getType()->isSized())
-    return ValueLatticeElement::getOverdefined();
-
   // Filter out casts we don't know how to reason about before attempting to
   // recurse on our operand.  This can cut a long search short if we know we're
   // not going to be able to get any useful information anways.
   switch (CI->getOpcode()) {
   case Instruction::Trunc:
   case Instruction::SExt:
   case Instruction::ZExt:
-  case Instruction::BitCast:
     break;
   default:
     // Unhandled instructions are overdefined.