🚸 Improved error reporting in HSF and Path Simulator (#431)

## Description

This PR improves the error management of the HSF and the Path Simulator
and makes them report a little more user-friendly error messages if
certain constructs of a circuit are not supported by the simulators.

Fixes #251 and #269

## Checklist:

<!---
This checklist serves as a reminder of a couple of things that ensure
your pull request will be merged swiftly.
-->

- [x] The pull request only contains commits that are related to it.
- [x] I have added appropriate tests and documentation.
- [x] I have made sure that all CI jobs on GitHub pass.
- [x] The pull request introduces no new warnings and follows the
project's style guidelines.

Author: burgholzer

cmake/ExternalDependencies.cmake

@@ -22,7 +22,7 @@ endif()
 # cmake-format: off
 set(MQT_CORE_VERSION 2.6.1
     CACHE STRING "MQT Core version")
-set(MQT_CORE_REV "9be91674dddcf1f73143d9509e8e4ad806f47592"
+set(MQT_CORE_REV "cd2e7678aac769c986c6ee1db76c4e03aea053a5"
     CACHE STRING "MQT Core identifier (tag, branch or commit hash)")
 set(MQT_CORE_REPO_OWNER "cda-tum"
     CACHE STRING "MQT Core repository owner (change when using a fork)")
@@ -75,7 +75,7 @@ set(TF_BUILD_PROFILER
     OFF
     CACHE INTERNAL "")
 set(TF_VERSION
-    3.6.0
+    3.7.0
     CACHE STRING "Taskflow version")
 set(TF_URL https://github.com/taskflow/taskflow/archive/refs/tags/v${TF_VERSION}.tar.gz)
 if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.24)

include/HybridSchrodingerFeynmanSimulator.hpp

@@ -30,6 +30,7 @@ class HybridSchrodingerFeynmanSimulator : public CircuitSimulator<Config> {
       const std::size_t nthreads_ = 2)
       : CircuitSimulator<Config>(std::move(qc_), approxInfo_), mode(mode_),
         nthreads(nthreads_) {
+    qc::CircuitOptimizer::flattenOperations(*(CircuitSimulator<Config>::qc));
     // remove final measurements
     qc::CircuitOptimizer::removeFinalMeasurements(
         *(CircuitSimulator<Config>::qc));
@@ -48,6 +49,7 @@ class HybridSchrodingerFeynmanSimulator : public CircuitSimulator<Config> {
       : CircuitSimulator<Config>(std::move(qc_), approxInfo_, seed_),
         mode(mode_), nthreads(nthreads_) {
     // remove final measurements
+    qc::CircuitOptimizer::flattenOperations(*(CircuitSimulator<Config>::qc));
     qc::CircuitOptimizer::removeFinalMeasurements(
         *(CircuitSimulator<Config>::qc));
   }

src/HybridSchrodingerFeynmanSimulator.cpp

@@ -40,27 +40,52 @@ HybridSchrodingerFeynmanSimulator<Config>::getNDecisions(qc::Qubit splitQubit) {
     if (op->getType() == qc::Barrier) {
       continue;
     }
-    if (op->isStandardOperation()) {
-      bool targetInLowerSlice = false;
-      bool targetInUpperSlice = false;
-      bool controlInLowerSlice = false;
-      bool controlInUpperSlice = false;
-      for (const auto& target : op->getTargets()) {
-        targetInLowerSlice = targetInLowerSlice || target < splitQubit;
-        targetInUpperSlice = targetInUpperSlice || target >= splitQubit;
+
+    assert(op->isStandardOperation());
+
+    bool targetInLowerSlice = false;
+    bool targetInUpperSlice = false;
+    bool controlInLowerSlice = false;
+    size_t nControlsInLowerSlice = 0;
+    bool controlInUpperSlice = false;
+    size_t nControlsInUpperSlice = 0;
+    for (const auto& target : op->getTargets()) {
+      targetInLowerSlice = targetInLowerSlice || target < splitQubit;
+      targetInUpperSlice = targetInUpperSlice || target >= splitQubit;
+    }
+    for (const auto& control : op->getControls()) {
+      if (control.qubit < splitQubit) {
+        controlInLowerSlice = true;
+        nControlsInLowerSlice++;
+      } else {
+        controlInUpperSlice = true;
+        nControlsInUpperSlice++;
       }
-      for (const auto& control : op->getControls()) {
-        controlInLowerSlice = controlInLowerSlice || control.qubit < splitQubit;
-        controlInUpperSlice =
-            controlInUpperSlice || control.qubit >= splitQubit;
+    }
+
+    if (targetInLowerSlice && targetInUpperSlice) {
+      throw std::invalid_argument(
+          "Multiple targets spread across the cut through the circuit are not "
+          "supported at the moment as this would require actually computing "
+          "the Schmidt decomposition of the gate being cut.");
+    }
+
+    if (targetInLowerSlice && controlInUpperSlice) {
+      if (nControlsInUpperSlice > 1) {
+        throw std::invalid_argument(
+            "Multiple controls in the control part of the gate being cut are "
+            "not supported at the moment as this would require actually "
+            "computing the Schmidt decomposition of the gate being cut.");
       }
-      if ((targetInLowerSlice && controlInUpperSlice) ||
-          (targetInUpperSlice && controlInLowerSlice)) {
-        ndecisions++;
+      ++ndecisions;
+    } else if (targetInUpperSlice && controlInLowerSlice) {
+      if (nControlsInLowerSlice > 1) {
+        throw std::invalid_argument(
+            "Multiple controls in the control part of the gate being cut are "
+            "not supported at the moment as this would require actually "
+            "computing the Schmidt decomposition of the gate being cut.");
       }
-    } else {
-      throw std::invalid_argument(
-          "Only StandardOperations are supported for now.");
+      ++ndecisions;
     }
   }
   return ndecisions;
@@ -77,11 +102,10 @@ qc::VectorDD HybridSchrodingerFeynmanSimulator<Config>::simulateSlicing(
       controls);
 
   for (const auto& op : *CircuitSimulator<Config>::qc) {
-    if (op->isUnitary()) {
-      [[maybe_unused]] auto l = lower.apply(sliceDD, op);
-      [[maybe_unused]] auto u = upper.apply(sliceDD, op);
-      assert(l == u);
-    }
+    assert(op->isUnitary());
+    [[maybe_unused]] auto l = lower.apply(sliceDD, op);
+    [[maybe_unused]] auto u = upper.apply(sliceDD, op);
+    assert(l == u);
     sliceDD->garbageCollect();
   }
 
@@ -97,76 +121,67 @@ bool HybridSchrodingerFeynmanSimulator<Config>::Slice::apply(
     std::unique_ptr<dd::Package<Config>>& sliceDD,
     const std::unique_ptr<qc::Operation>& op) {
   bool isSplitOp = false;
-  if (dynamic_cast<qc::StandardOperation*>(op.get()) !=
-      nullptr) { // TODO change control and target if wrong direction
-    qc::Targets opTargets{};
-    qc::Controls opControls{};
-
-    // check targets
-    bool targetInSplit = false;
-    bool targetInOtherSplit = false;
-    for (const auto& target : op->getTargets()) {
-      if (start <= target && target <= end) {
-        opTargets.push_back(target);
-        targetInSplit = true;
-      } else {
-        targetInOtherSplit = true;
-      }
-    }
-
-    if (targetInSplit && targetInOtherSplit && !op->getControls().empty()) {
-      throw std::invalid_argument("Multiple Targets that are in different "
-                                  "slices are not supported at the moment");
+  assert(op->isStandardOperation());
+  qc::Targets opTargets{};
+  qc::Controls opControls{};
+
+  // check targets
+  bool targetInSplit = false;
+  bool targetInOtherSplit = false;
+  for (const auto& target : op->getTargets()) {
+    if (start <= target && target <= end) {
+      opTargets.emplace_back(target);
+      targetInSplit = true;
+    } else {
+      targetInOtherSplit = true;
     }
+  }
 
-    // check controls
-    for (const auto& control : op->getControls()) {
-      if (start <= control.qubit && control.qubit <= end) {
-        opControls.emplace(control.qubit, control.type);
-      } else { // other controls are set to the corresponding value
-        if (targetInSplit) {
-          isSplitOp = true;
-          const bool nextControl = getNextControl();
-          if ((control.type == qc::Control::Type::Pos &&
-               !nextControl) || // break if control is not activated
-              (control.type == qc::Control::Type::Neg && nextControl)) {
-            nDecisionsExecuted++;
-            return true;
-          }
+  // Ensured in the getNDecisions function
+  assert(!(targetInSplit && targetInOtherSplit));
+
+  // check controls
+  for (const auto& control : op->getControls()) {
+    if (start <= control.qubit && control.qubit <= end) {
+      opControls.emplace(control);
+    } else { // other controls are set to the corresponding value
+      if (targetInSplit) {
+        isSplitOp = true;
+        const bool nextControl = getNextControl();
+        // break if control is not activated
+        if ((control.type == qc::Control::Type::Pos && !nextControl) ||
+            (control.type == qc::Control::Type::Neg && nextControl)) {
+          nDecisionsExecuted++;
+          return true;
         }
       }
     }
+  }
 
-    if (targetInOtherSplit && !opControls.empty()) { // control slice for split
-      if (opControls.size() > 1) {
-        throw std::invalid_argument(
-            "Multiple controls in control slice of operation are not supported "
-            "at the moment");
-      }
+  if (targetInOtherSplit && !opControls.empty()) { // control slice for split
+    // Ensured in the getNDecisions function
+    assert(opControls.size() == 1);
 
-      isSplitOp = true;
-      const bool control = getNextControl();
-      for (const auto& c : opControls) {
-        auto tmp = edge;
-        edge = sliceDD->deleteEdge(
-            edge, static_cast<dd::Qubit>(c.qubit),
-            control != (c.type == qc::Control::Type::Neg) ? 0 : 1);
-        // TODO incref and decref could be integrated in delete edge
-        sliceDD->incRef(edge);
-        sliceDD->decRef(tmp);
-      }
-    } else if (targetInSplit) { // target slice for split or operation in split
-      const auto& param = op->getParameter();
-      qc::StandardOperation newOp(opControls, opTargets, op->getType(), param);
+    isSplitOp = true;
+    const bool control = getNextControl();
+    for (const auto& c : opControls) {
       auto tmp = edge;
-      edge = sliceDD->multiply(dd::getDD(&newOp, *sliceDD), edge);
+      edge = sliceDD->deleteEdge(
+          edge, static_cast<dd::Qubit>(c.qubit),
+          control != (c.type == qc::Control::Type::Neg) ? 0 : 1);
+      // TODO incref and decref could be integrated in delete edge
       sliceDD->incRef(edge);
       sliceDD->decRef(tmp);
     }
-  } else {
-    throw std::invalid_argument(
-        "Only StandardOperations are supported for now.");
+  } else if (targetInSplit) { // target slice for split or operation in split
+    const auto& param = op->getParameter();
+    qc::StandardOperation newOp(opControls, opTargets, op->getType(), param);
+    auto tmp = edge;
+    edge = sliceDD->multiply(dd::getDD(&newOp, *sliceDD), edge);
+    sliceDD->incRef(edge);
+    sliceDD->decRef(tmp);
   }
+
   if (isSplitOp) {
     nDecisionsExecuted++;
   }
@@ -176,6 +191,20 @@ bool HybridSchrodingerFeynmanSimulator<Config>::Slice::apply(
 template <class Config>
 std::map<std::string, std::size_t>
 HybridSchrodingerFeynmanSimulator<Config>::simulate(std::size_t shots) {
+  if (CircuitSimulator<Config>::qc->isDynamic()) {
+    throw std::invalid_argument(
+        "Dynamic quantum circuits containing mid-circuit measurements, resets, "
+        "or classical control flow are not supported by this simulator.");
+  }
+
+  for (const auto& op : *CircuitSimulator<Config>::qc) {
+    if (!op->isStandardOperation()) {
+      throw std::invalid_argument("This simulator only supports regular gates "
+                                  "(`StandardOperation`). \"" +
+                                  op->getName() + "\" is not supported.");
+    }
+  }
+
   auto nqubits = CircuitSimulator<Config>::getNumberOfQubits();
   auto splitQubit = static_cast<qc::Qubit>(nqubits / 2);
   if (mode == Mode::DD) {

src/PathSimulator.cpp

@@ -142,6 +142,12 @@ PathSimulator<Config>::SimulationPath::SimulationPath(
 template <class Config>
 std::map<std::string, std::size_t>
 PathSimulator<Config>::simulate(std::size_t shots) {
+  if (CircuitSimulator<Config>::qc->isDynamic()) {
+    throw std::invalid_argument(
+        "Dynamic quantum circuits containing mid-circuit measurements, resets, "
+        "or classical control flow are not supported by this simulator.");
+  }
+
   // build task graph from simulation path
   constructTaskGraph();
   /// Enable the following statements to generate a .dot file of the resulting

test/test_hybridsim.cpp

@@ -1,6 +1,7 @@
 #include "CircuitSimulator.hpp"
 #include "HybridSchrodingerFeynmanSimulator.hpp"
 #include "ir/QuantumComputation.hpp"
+#include "ir/operations/OpType.hpp"
 
 #include <cstdlib>
 #include <gtest/gtest.h>
@@ -81,18 +82,6 @@ TEST(HybridSimTest, TrivialParallelAmplitude) {
   EXPECT_NEAR(static_cast<double>(it->second), 2048, 128);
 }
 
-TEST(HybridSimTest, NonStandardOperation) {
-  auto quantumComputation = std::make_unique<qc::QuantumComputation>(1, 1);
-  quantumComputation->h(0);
-  quantumComputation->measure(0, 0);
-  quantumComputation->barrier(0);
-  quantumComputation->h(0);
-  quantumComputation->measure(0, 0);
-
-  HybridSchrodingerFeynmanSimulator ddsim(std::move(quantumComputation));
-  EXPECT_THROW(ddsim.simulate(0), std::invalid_argument);
-}
-
 TEST(HybridSimTest, TooManyQubitsForVectorTest) {
   auto qc = std::make_unique<qc::QuantumComputation>(61);
   const HybridSchrodingerFeynmanSimulator<> ddsim(
@@ -204,3 +193,41 @@ TEST(HybridSimTest, RegressionTestAmplitudeModeMoreChunksAsThreads) {
   EXPECT_EQ(result.begin()->first, "10");
   EXPECT_EQ(result.begin()->second, 1024U);
 }
+
+TEST(HybridSimTest, DynamicCircuitSupport) {
+  auto qc = std::make_unique<qc::QuantumComputation>(1, 1);
+  qc->h(0);
+  qc->measure(0, 0);
+  qc->classicControlled(qc::X, 0, {0, 1}, 1);
+  std::cout << *qc << "\n";
+
+  HybridSchrodingerFeynmanSimulator sim(std::move(qc));
+  EXPECT_THROW(sim.simulate(1024), std::invalid_argument);
+}
+
+TEST(HybridSimTest, TwoTargetGateSupport) {
+  auto qc = std::make_unique<qc::QuantumComputation>(2);
+  qc->rzz(1., 0, 1);
+  std::cout << *qc << "\n";
+
+  HybridSchrodingerFeynmanSimulator sim(std::move(qc));
+  EXPECT_THROW(sim.simulate(1024), std::invalid_argument);
+}
+
+TEST(HybridSimTest, TwoControlGateSupportLowerHalf) {
+  auto qc = std::make_unique<qc::QuantumComputation>(4);
+  qc->mcx({0, 1}, 2);
+  std::cout << *qc << "\n";
+
+  HybridSchrodingerFeynmanSimulator sim(std::move(qc));
+  EXPECT_THROW(sim.simulate(1024), std::invalid_argument);
+}
+
+TEST(HybridSimTest, TwoControlGateSupportUpperHalf) {
+  auto qc = std::make_unique<qc::QuantumComputation>(4);
+  qc->mcx({3, 2}, 1);
+  std::cout << *qc << "\n";
+
+  HybridSchrodingerFeynmanSimulator sim(std::move(qc));
+  EXPECT_THROW(sim.simulate(1024), std::invalid_argument);
+}

test/test_path_sim.cpp

@@ -3,6 +3,7 @@
 #include "dd/DDDefinitions.hpp"
 #include "dd/Export.hpp"
 #include "ir/QuantumComputation.hpp"
+#include "ir/operations/OpType.hpp"
 
 #include <complex>
 #include <gtest/gtest.h>
@@ -295,3 +296,14 @@ TEST(TaskBasedSimTest, SimpleCircuitGatecostConfigurationObject) {
     std::cout << state << ": " << count << "\n";
   }
 }
+
+TEST(TaskBasedSimTest, DynamicCircuitSupport) {
+  auto qc = std::make_unique<qc::QuantumComputation>(1, 1);
+  qc->h(0);
+  qc->measure(0, 0);
+  qc->classicControlled(qc::X, 0, {0, 1}, 1);
+  std::cout << *qc << "\n";
+
+  PathSimulator sim(std::move(qc));
+  EXPECT_THROW(sim.simulate(1024), std::invalid_argument);
+}