set GPhase complexity to 0 and fix complexity calculation for backtracking

Author: taminob

mlir/include/mlir/Passes/Decomposition/Helpers.h

@@ -217,7 +217,7 @@ template <typename T, int N, int M>
     return (numOfQubits - 1) * multiQubitFactor;
   }
   if (type == qc::GPhase) {
-    return 2;
+    return 0;
   }
   return 1;
 }

mlir/lib/Passes/Patterns/GateDecompositionPattern.cpp

@@ -464,6 +464,7 @@ struct GateDecompositionPattern final
       auto prependSingleQubitGate = [&](UnitaryOpInterface op) {
         inQubits[qubitId] = op.getInputQubit(0);
         gates.insert(gates.begin(), {.op = op, .qubitIds = {qubitId}});
+        complexity += helpers::getComplexity(helpers::getQcType(op), 1);
         // outQubits do not need to be updated because the final out qubit is
         // already fixed
       };