[llvm][Type] Return fixed size for scalar types. [NFC]

[fpetrogalli]

Summary

It is safe to assume that the TypeSize associated to scalar types has
a fixed size.

This avoids an implicit cast of TypeSize to integer inside
Type::getScalarSizeInBits(), as such implicit cast is deprecated.

[efriedma]

LGTM

llvm/lib/IR/Type.cpp

135–136

"It is safe"?

[fpetrogalli]

Fixed the typo in the comment.

llvm/lib/IR/Type.cpp

case Type::VectorTyID: {
     const VectorType *VTy = cast<VectorType>(this);
     return TypeSize(VTy->getBitWidth(), VTy->isScalable());
   }
   default: return TypeSize::Fixed(0);
   }
 }
 
 unsigned Type::getScalarSizeInBits() const {
-  return getScalarType()->getPrimitiveSizeInBits();
+  // It is safe to assume that the scalar types have a fixed size.
+  return getScalarType()->getPrimitiveSizeInBits().getFixedSize();
 }
 
 int Type::getFPMantissaWidth() const {
   if (auto *VTy = dyn_cast<VectorType>(this))
     return VTy->getElementType()->getFPMantissaWidth();
   assert(isFloatingPointTy() && "Not a floating point type!");
   if (getTypeID() == HalfTyID) return 11;
   if (getTypeID() == FloatTyID) return 24;