class_docstr: `if` statement with backed dynamic shape predicate will be specialized into
  one particular branch and generate a guard. However, export will fail if the
  the dimension is marked as dynamic shape from higher level API.
class_docstr_tok: ["`","if","`","statement","with","backed","dynamic","shape","predicate","will","be","specialized","into","one","particular","branch","and","generate","a","guard",".","However",",","export","will","fail","if","the","the","dimension","is","marked","as","dynamic","shape","from","higher","level","API","."]
code: def forward(self, x):
      if x.shape[0] == 3:
          return x.cos()
  
      return x.sin()
  
imports: import torch
  from torch._export.db.case import export_case
label_desc: Use image node_id 1 for calling the DynamicShapeIfGuard obj's underlying member method code with example usage: obj.forward(x) and returns: x, x