Merge pull request #222 from BQSKit/fix-identity-rebase

Fix identity rebase

bqskit/compiler/compile.py

@@ -1014,7 +1014,7 @@ def build_multi_qudit_retarget_workflow(
                     ),
                     RestoreModelConnevtivityPass(),
                 ],
-                AutoRebase2QuditGatePass(3, 5),
+                AutoRebase2QuditGatePass(3, 5, synthesis_epsilon),
             ),
             ScanningGateRemovalPass(
                 success_threshold=synthesis_epsilon,

bqskit/passes/retarget/auto.py

@@ -9,6 +9,7 @@
 from bqskit.ir.opt.cost.functions import HilbertSchmidtResidualsGenerator
 from bqskit.ir.opt.cost.generator import CostFunctionGenerator
 from bqskit.passes.retarget.two import Rebase2QuditGatePass
+from bqskit.qis.unitary import UnitaryMatrix
 from bqskit.runtime import get_runtime
 from bqskit.utils.typing import is_integer
 from bqskit.utils.typing import is_real_number
@@ -112,6 +113,13 @@ async def run(self, circuit: Circuit, data: PassData) -> None:
 
         target = self.get_target(circuit, data)
 
+        if isinstance(target, UnitaryMatrix):
+            identity = UnitaryMatrix.identity(target.dim, target.radixes)
+            if target.get_distance_from(identity) < self.success_threshold:
+                _logger.debug('Target is identity, returning empty circuit.')
+                circuit.clear()
+                return
+
         for g in old_gates:
             # Track retries to check for no progress
             num_retries = 0

bqskit/passes/retarget/two.py

@@ -13,6 +13,7 @@
 from bqskit.ir.opt.cost.functions import HilbertSchmidtResidualsGenerator
 from bqskit.ir.opt.cost.generator import CostFunctionGenerator
 from bqskit.ir.point import CircuitPoint as Point
+from bqskit.qis.unitary import UnitaryMatrix
 from bqskit.runtime import get_runtime
 from bqskit.utils.typing import is_integer
 from bqskit.utils.typing import is_real_number
@@ -164,6 +165,13 @@ async def run(self, circuit: Circuit, data: PassData) -> None:
 
         target = self.get_target(circuit, data)
 
+        if isinstance(target, UnitaryMatrix):
+            identity = UnitaryMatrix.identity(target.dim, target.radixes)
+            if target.get_distance_from(identity) < self.success_threshold:
+                _logger.debug('Target is identity, returning empty circuit.')
+                circuit.clear()
+                return
+
         for g in self.gates:
             # Track retries to check for no progress
             num_retries = 0
@@ -188,6 +196,7 @@ async def run(self, circuit: Circuit, data: PassData) -> None:
                     circuit.point(g),
                     self.gates,
                 )
+
                 circuits_with_new_gate = []
                 for circ in self.circs:
                     circuit_copy = circuit.copy()

tests/compiler/compile/test_corner_cases.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+from bqskit.compiler.compile import compile
+from bqskit.compiler.compiler import Compiler
+from bqskit.ir.lang.qasm2 import OPENQASM2Language
+
+
+def test_cry_identity_corner_case(compiler: Compiler) -> None:
+    qasm = """
+        OPENQASM 2.0;
+        include "qelib1.inc";
+        qreg q[5];
+        creg meas[5];
+        cry(0) q[0],q[2];
+        cry(0) q[1],q[2];
+    """
+    circuit = OPENQASM2Language().decode(qasm)
+    _ = compile(circuit, optimization_level=1, seed=10)
+    # Should finish