Ported nnizer transform to XACC

I realized that this was buried in an ExaTN-visitor only folder. This made it unusable for others such as ITensor (when users don't compile w/ ExaTN)
Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

quantum/plugins/optimizers/CMakeLists.txt

@@ -13,7 +13,7 @@
 set (LIBRARY_NAME xacc-circuit-optimizers)
 
 file (GLOB_RECURSE HEADERS *.hpp)
-file (GLOB SRC simple/*.cpp OptimizersActivator.cpp pulse/*.cpp gate_merge/*.cpp)
+file (GLOB SRC simple/*.cpp OptimizersActivator.cpp pulse/*.cpp gate_merge/*.cpp lnn_transform/*.cpp)
 
 # Set up dependencies to resources to track changes
 usFunctionGetResourceSource(TARGET ${LIBRARY_NAME} OUT SRC)
@@ -39,7 +39,7 @@ usFunctionEmbedResources(TARGET ${LIBRARY_NAME}
     manifest.json
   )
 
-target_include_directories(${LIBRARY_NAME} PUBLIC simple pulse gate_merge ${CMAKE_SOURCE_DIR}/tpls/eigen ${CMAKE_SOURCE_DIR}/tpls/exprtk)
+target_include_directories(${LIBRARY_NAME} PUBLIC simple pulse gate_merge lnn_transform ${CMAKE_SOURCE_DIR}/tpls/eigen ${CMAKE_SOURCE_DIR}/tpls/exprtk)
 target_link_libraries(${LIBRARY_NAME} xacc xacc-quantum-gate)
 
 if(APPLE)
@@ -57,6 +57,7 @@ if(XACC_BUILD_TESTS)
   add_subdirectory(simple/tests)
   add_subdirectory(pulse/tests)
   add_subdirectory(gate_merge/tests)
+  add_subdirectory(lnn_transform/tests)
 endif()
 
 add_subdirectory(qsearch)
\ No newline at end of file

quantum/plugins/optimizers/OptimizersActivator.cpp

@@ -14,7 +14,8 @@
 #include "default_placement.hpp"
 #include "GateMergeOptimizer.hpp"
 #include "PulseTransform.hpp"
-#include "GateFusion.hpp" 
+#include "GateFusion.hpp"
+#include "NearestNeighborTransform.hpp"
 // #include "qsearch.hpp"
 #include "cppmicroservices/BundleActivator.h"
 #include "cppmicroservices/BundleContext.h"
@@ -28,40 +29,40 @@ namespace {
 
 /**
  */
-class US_ABI_LOCAL OptimizersActivator: public BundleActivator {
+class US_ABI_LOCAL OptimizersActivator : public BundleActivator {
 
 public:
+  OptimizersActivator() {}
 
-	OptimizersActivator() {
-	}
+  /**
+   */
+  void Start(BundleContext context) {
+    auto c4 = std::make_shared<xacc::quantum::CircuitOptimizer>();
+    context.RegisterService<xacc::IRTransformation>(c4);
 
-	/**
-	 */
-	void Start(BundleContext context) {
-		auto c4 = std::make_shared<xacc::quantum::CircuitOptimizer>();
-        context.RegisterService<xacc::IRTransformation>(c4);
+    auto c5 = std::make_shared<xacc::quantum::DefaultPlacement>();
+    context.RegisterService<xacc::IRTransformation>(c5);
 
-        auto c5 = std::make_shared<xacc::quantum::DefaultPlacement>();
-        context.RegisterService<xacc::IRTransformation>(c5);
+    // auto c6 = std::make_shared<xacc::quantum::QsearchOptimizer>();
+    // context.RegisterService<xacc::IRTransformation>(c6);
 
+    context.RegisterService<xacc::IRTransformation>(c5);
+    context.RegisterService<xacc::IRTransformation>(
+        std::make_shared<xacc::quantum::PulseTransform>());
+    context.RegisterService<GateFuser>(std::make_shared<GateFuser>());
+    context.RegisterService<xacc::IRTransformation>(
+        std::make_shared<xacc::quantum::MergeSingleQubitGatesOptimizer>());
+    context.RegisterService<xacc::IRTransformation>(
+        std::make_shared<xacc::quantum::MergeTwoQubitBlockOptimizer>());
+    context.RegisterService<xacc::IRTransformation>(
+        std::make_shared<xacc::quantum::NearestNeighborTransform>());
+  }
 
-        // auto c6 = std::make_shared<xacc::quantum::QsearchOptimizer>();
-		// context.RegisterService<xacc::IRTransformation>(c6);
-		
-        context.RegisterService<xacc::IRTransformation>(c5);
-        context.RegisterService<xacc::IRTransformation>(std::make_shared<xacc::quantum::PulseTransform>());
-		context.RegisterService<GateFuser>(std::make_shared<GateFuser>());
-		context.RegisterService<xacc::IRTransformation>(std::make_shared<xacc::quantum::MergeSingleQubitGatesOptimizer>());
-		context.RegisterService<xacc::IRTransformation>(std::make_shared<xacc::quantum::MergeTwoQubitBlockOptimizer>());
-	}
-
-	/**
-	 */
-	void Stop(BundleContext /*context*/) {
-	}
-
+  /**
+   */
+  void Stop(BundleContext /*context*/) {}
 };
 
-}
+} // namespace
 
 CPPMICROSERVICES_EXPORT_BUNDLE_ACTIVATOR(OptimizersActivator)

quantum/plugins/optimizers/lnn_transform/NearestNeighborTransform.cpp

+#include "NearestNeighborTransform.hpp"
+#include "InstructionIterator.hpp"
+
+namespace xacc {
+namespace quantum {
+
+void NearestNeighborTransform::apply(
+    std::shared_ptr<CompositeInstruction> in_program,
+    const std::shared_ptr<Accelerator> in_accelerator,
+    const HeterogeneousMap &in_options) {
+  // The option is qubit-distance (default is 1, adjacent qubits)
+  // any 2-qubit gates that are further than this distance are converted into
+  // Swap + Original Gate (at qubit distance) + Swap
+  // Strategy: meet in the middle:
+  // e.g. CNOT q0, q9;  qubit-distance = 2 (max distance is next neighbor,
+  // e.g. CNOT q0, q2; CNOT q7, q9 are okay) then we will Swap q0->q4; q9->q6;
+  // then CNOT q4, q6; then Swap q4->q0 and Swap q6->q9
+
+  int maxDistance = 1;
+  if (in_options.keyExists<int>("max-distance")) {
+    maxDistance = in_options.get<int>("max-distance");
+  }
+
+  auto provider = xacc::getIRProvider("quantum");
+  auto flattenedProgram =
+      provider->createComposite(in_program->name() + "_Flattened");
+  InstructionIterator it(in_program);
+  while (it.hasNext()) {
+    auto nextInst = it.next();
+    if (nextInst->isEnabled() && !nextInst->isComposite()) {
+      flattenedProgram->addInstruction(nextInst->clone());
+    }
+  }
+
+  auto transformedProgram =
+      provider->createComposite(in_program->name() + "_Transformed");
+  for (int i = 0; i < flattenedProgram->nInstructions(); ++i) {
+    auto inst = flattenedProgram->getInstruction(i);
+
+    const auto exceedMaxDistance = [&maxDistance](int q1, int q2) -> bool {
+      return std::abs(q1 - q2) > maxDistance;
+    };
+
+    if (inst->bits().size() == 2 &&
+        exceedMaxDistance(inst->bits()[0], inst->bits()[1])) {
+      const int origLowerIdx = std::min({inst->bits()[0], inst->bits()[1]});
+      const int origUpperIdx = std::max({inst->bits()[0], inst->bits()[1]});
+      size_t lowerIdx = origLowerIdx;
+      size_t upperIdx = origUpperIdx;
+      // Insert swaps
+      for (;; /*Break inside*/) {
+        transformedProgram->addInstruction(
+            provider->createInstruction("Swap", {lowerIdx, lowerIdx + 1}));
+        lowerIdx++;
+
+        if (!exceedMaxDistance(lowerIdx, upperIdx)) {
+          break;
+        }
+
+        transformedProgram->addInstruction(
+            provider->createInstruction("Swap", {upperIdx, upperIdx - 1}));
+        upperIdx--;
+
+        if (!exceedMaxDistance(lowerIdx, upperIdx)) {
+          break;
+        }
+      }
+
+      // Run new gate
+      const bool bitCompare = inst->bits()[0] < inst->bits()[1];
+      inst->setBits(bitCompare ? std::vector<size_t>{lowerIdx, upperIdx}
+                               : std::vector<size_t>{upperIdx, lowerIdx});
+      transformedProgram->addInstruction(inst);
+
+      // Insert swaps
+      for (size_t i = lowerIdx; i > origLowerIdx; --i) {
+        transformedProgram->addInstruction(
+            provider->createInstruction("Swap", {i, i - 1}));
+      }
+
+      for (size_t i = upperIdx; i < origUpperIdx; ++i) {
+        transformedProgram->addInstruction(
+            provider->createInstruction("Swap", {i, i + 1}));
+      }
+    } else {
+      transformedProgram->addInstruction(inst);
+    }
+  }
+  // DEBUG:
+  // std::cout << "After transform: \n" <<  transformedProgram->toString() <<
+  // "\n";
+  in_program->clear();
+  in_program->addInstructions(transformedProgram->getInstructions());
+
+  return;
+}
+} // namespace quantum
+} // namespace xacc

quantum/plugins/optimizers/lnn_transform/NearestNeighborTransform.hpp

+#pragma once
+#include "xacc.hpp"
+#include "IRTransformation.hpp"
+
+namespace xacc {
+namespace quantum {
+class NearestNeighborTransform : public IRTransformation {
+public:
+  NearestNeighborTransform() {}
+  void apply(std::shared_ptr<CompositeInstruction> in_program,
+             const std::shared_ptr<Accelerator> in_accelerator,
+             const HeterogeneousMap &in_options = {}) override;
+
+  const IRTransformationType type() const override {
+    return IRTransformationType::Placement;
+  }
+  const std::string name() const override { return "nnizer"; }
+  const std::string description() const override { return ""; }
+};
+} // namespace quantum
+} // namespace xacc
\ No newline at end of file

quantum/plugins/optimizers/lnn_transform/tests/CMakeLists.txt

+add_xacc_test(NearestNeighborTransform)
+target_link_libraries(NearestNeighborTransformTester xacc-quantum-gate xacc-circuit-optimizers)
\ No newline at end of file

quantum/plugins/optimizers/lnn_transform/tests/NearestNeighborTransformTester.cpp

+#include <memory>
+#include <gtest/gtest.h>
+#include "xacc.hpp"
+#include "xacc_service.hpp"
+
+namespace {
+int countSwap(const std::shared_ptr<xacc::CompositeInstruction> in_program) {
+  int result = 0;
+
+  for (int i = 0; i < in_program->nInstructions(); ++i) {
+    auto inst = in_program->getInstruction(i);
+    if (inst->name() == "Swap") {
+      result++;
+    }
+  }
+
+  return result;
+}
+} // namespace
+
+TEST(NearestNeighborTransformTester, checkSimple) {
+  auto c = xacc::getService<xacc::Compiler>("xasm");
+  auto f = c->compile(R"(__qpu__ void test1(qbit q) {
+        X(q[0]);
+        CNOT(q[1], q[3]);
+        H(q[7]);
+        CNOT(q[6], q[7]);
+        CNOT(q[7], q[3]);
+        X(q[6]);
+        Swap(q[4], q[9]);
+        S(q[5]);
+    })")
+               ->getComposites()[0];
+
+  auto provider = xacc::getIRProvider("quantum");
+
+  auto ir = provider->createIR();
+  ir->addComposite(f);
+  auto opt = xacc::getService<xacc::IRTransformation>("nnizer");
+  const auto nInstBefore = f->nInstructions();
+  const auto nbSwapGateBefore = countSwap(f);
+
+  // No option: default max distance = 1
+  opt->apply(f, nullptr);
+  std::cout << "After LNN transform: \n" << f->toString() << "\n";
+
+  const auto nbSwapGateAfter = countSwap(f);
+  const auto nInstAfter = f->nInstructions();
+  const auto newSwapGateCount = nbSwapGateAfter - nbSwapGateBefore;
+
+  EXPECT_EQ(nInstAfter, nInstBefore + newSwapGateCount);
+  // Check that no 2-qubit gates have distance > 1
+  for (int i = 0; i < f->nInstructions(); ++i) {
+    auto inst = f->getInstruction(i);
+    if (inst->bits().size() == 2) {
+      const int distance = inst->bits()[0] - inst->bits()[1];
+      EXPECT_EQ(std::abs(distance), 1);
+    }
+  }
+}
+
+TEST(NearestNeighborTransformTester, checkDistanceConfig) {
+  auto c = xacc::getService<xacc::Compiler>("xasm");
+  auto f = c->compile(R"(__qpu__ void test2(qbit q) {
+        X(q[0]);
+        CNOT(q[1], q[9]);
+        H(q[7]);
+        CNOT(q[3], q[1]);
+    })")
+               ->getComposites()[0];
+
+  auto provider = xacc::getIRProvider("quantum");
+
+  auto ir = provider->createIR();
+  ir->addComposite(f);
+  auto opt = xacc::getService<xacc::IRTransformation>("nnizer");
+  const auto nInstBefore = f->nInstructions();
+  const auto nbSwapGateBefore = countSwap(f);
+  // max distance = 2
+  opt->apply(f, nullptr, {std::make_pair("max-distance", 2)});
+  std::cout << "After LNN transform: \n" << f->toString() << "\n";
+
+  const auto nbSwapGateAfter = countSwap(f);
+  const auto nInstAfter = f->nInstructions();
+  const auto newSwapGateCount = nbSwapGateAfter - nbSwapGateBefore;
+
+  EXPECT_EQ(nInstAfter, nInstBefore + newSwapGateCount);
+  auto lastInst = f->getInstruction(nInstAfter - 1);
+  // The last instruction is CNOT(q[3], q[1])
+  // (distance = 2, within the limit, hence no conversion)
+  EXPECT_STREQ(lastInst->name().c_str(), "CNOT");
+  EXPECT_EQ(lastInst->bits()[0], 3);
+  EXPECT_EQ(lastInst->bits()[1], 1);
+}
+
+int main(int argc, char **argv) {
+  xacc::Initialize();
+  ::testing::InitGoogleTest(&argc, argv);
+  auto ret = RUN_ALL_TESTS();
+  xacc::Finalize();
+  return ret;
+}