Revert "Set sympy.evaluate(False) on frequent code paths for phase tr…

…acking. (#6072)" (#6386)

With recent adoption of symengine for the performance critical path
with ParameterExpressions the workaround for large expression evaluation
in #6072 is no longer needed or applicable, except in environments
without symengine. However, with symengine available using the sympy
evaluate context adds noticeable overhead, both to import sympy (which
wouldn't be used otherwise) and to load the sympy evalue context
wrapper. This commit removes these as we shouldn't compromise performance
in the performance path to try and speed up a path with degraded
performance because symengine isn't available (32bit platforms).

This reverts commit f436f5a.

Co-authored-by: Kevin Krsulich <[email protected]>

qiskit/dagcircuit/dagcircuit.py

@@ -996,10 +996,7 @@ def substitute_node_with_dag(self, node, input_dag, wires=None):
                 in_dag.apply_operation_back(replay_node.op, replay_node.qargs, replay_node.cargs)
 
         if in_dag.global_phase:
-            from sympy import evaluate
-
-            with evaluate(False):
-                self.global_phase += in_dag.global_phase
+            self.global_phase += in_dag.global_phase
 
         if wires is None:
             wires = in_dag.wires

qiskit/transpiler/passes/basis/basis_translator.py

@@ -181,10 +181,7 @@ def run(self, dag):
                     dag.substitute_node(node, dag_op, inplace=True)
 
                     if bound_target_dag.global_phase:
-                        from sympy import evaluate
-
-                        with evaluate(False):
-                            dag.global_phase += bound_target_dag.global_phase
+                        dag.global_phase += bound_target_dag.global_phase
                 else:
                     dag.substitute_node_with_dag(node, bound_target_dag)
             else: