code: func propagateConstantDNF(ctx sessionctx.Context, conds []Expression) []Expression {
  	for i, cond := range conds {
  		if dnf, ok := cond.(*ScalarFunction); ok && dnf.FuncName.L == ast.LogicOr {
  			dnfItems := SplitDNFItems(cond)
  			for j, item := range dnfItems {
  				dnfItems[j] = ComposeCNFCondition(ctx, PropagateConstant(ctx, []Expression{item})...)
  			}
  			conds[i] = ComposeDNFCondition(ctx, dnfItems...)
  		}
  	}
  	return conds
  }
docs: // propagateConstantDNF find DNF item from CNF, and propagate constant inside DNF.