Speed-up OpenQASM compilation for long circuits

- Add a visitor to translate Staq's AST to XACC's IR directly.

- Add ability to add a vector of instructions to Composite without validation. These instructions are translated from a valid AST.
Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

quantum/gate/ir/Circuit.hpp

@@ -224,6 +224,21 @@ public:
     for (auto &i : insts)
       addInstruction(i);
   }
+
+  void addInstructions(const std::vector<InstPtr> &&insts,
+                       bool shouldValidate = true) override {
+    if (shouldValidate) {
+      for (auto &i : insts) {
+        addInstruction(i);
+      }
+    } else {
+      // Bypass instruction validation, append all the instructions directly.
+      instructions.insert(instructions.end(),
+                          std::make_move_iterator(insts.begin()),
+                          std::make_move_iterator(insts.end()));
+    }
+  }
+
   void clear() override { instructions.clear(); }
 
   bool hasChildren() const override { return !instructions.empty(); }

quantum/plugins/staq/compiler/staq_compiler.cpp

@@ -226,9 +226,37 @@ std::shared_ptr<IR> StaqCompiler::compile(const std::string &src,
       *prog, {false, transformations::default_overrides, "anc"});
 
   //   std::cout <<"PROG: " << *prog << "\n";
-  // Visit Program to find out how many qreg there are and
-  // use that to build up openqasm xacc function prototype
+  
+  // Determine the number of qreqs
+  internal_staq::CountQregs countQreq;
+  dynamic_cast<ast::Traverse &>(countQreq).visit(*prog);
+  const auto nbQreqs = countQreq.qregs.size() + ancillas.ancillas.size();
+  // Direct Staq's AST -> XACC's IR translation:
+  // This can only be used (reliably) for simple QASM source,
+  // that uses a single qreg (we can use simple qubit indexing to construct IR)
+  // Note: we don't handle *embedded* QASM source in this direct translate mode.
+  if (!isXaccKernel && nbQreqs == 1) {
+    // Create a temporary kernel name:
+    std::string name = "tmp";
+    if (xacc::hasCompiled(name)) {
+      int counter = 0;
+      while (true) {
+        name = "tmp" + std::to_string(counter);
+        if (!xacc::hasCompiled(name)) {
+          break;
+        }
+        counter++;
+      }
+    }
+
+    // Direct translation
+    internal_staq::StaqToIr translate(name);
+    translate.visit(*prog);
+    return translate.getIr();
+  }
 
+  // Otherwise, translate Staq's AST to XASM source string
+  // then recompile.
   internal_staq::StaqToXasm translate;
   translate.visit(*prog);
 

quantum/plugins/staq/compiler/tests/StaqCompilerTester.in.cpp

@@ -15,6 +15,11 @@
 #include "xacc.hpp"
 #include "xacc_service.hpp"
 
+namespace {
+  // CU1 decompose: 5 instructions
+  constexpr int CU1_DECOMP_N_INSTS = 5;
+}
+
 TEST(StaqCompilerTester, checkCphase) {
 
   auto src = R"#(
@@ -34,9 +39,10 @@ measure q[2] -> c[2];)#";
 
   auto hello = IR->getComposites()[0];
   std::cout << "HELLO:\n" << hello->toString() << "\n";
-
-
+  const int expectedNinsts = 7 + CU1_DECOMP_N_INSTS;
+  EXPECT_EQ(hello->nInstructions(), expectedNinsts);
 }
+
 TEST(StaqCompilerTester, checkSimple) {
   auto compiler = xacc::getCompiler("staq");
   auto IR = compiler->compile(R"(
@@ -50,7 +56,8 @@ TEST(StaqCompilerTester, checkSimple) {
 
   auto hello = IR->getComposites()[0];
   std::cout << "HELLO:\n" << hello->toString() << "\n";
-
+  EXPECT_EQ(hello->nInstructions(), 5);
+  
   auto q = xacc::qalloc(2);
   q->setName("q");
   xacc::storeBuffer(q);
@@ -67,6 +74,7 @@ TEST(StaqCompilerTester, checkSimple) {
 
   hello = IR->getComposites()[0];
   std::cout << "HELLO:\n" << hello->toString() << "\n";
+  EXPECT_EQ(hello->nInstructions(), 5);
 }
 
 TEST(StaqCompilerTester, checkCanParse) {

quantum/plugins/staq/utils/staq_visitors.hpp

@@ -18,7 +18,8 @@
 #include "ast/traversal.hpp"
 #include <map>
 #include <iomanip>
-
+#include "xacc.hpp"
+#include "xacc_service.hpp"
 #include "AllGateVisitor.hpp"
 
 using namespace staq::ast;
@@ -110,6 +111,94 @@ public:
   }
 };
 
+// Staq AST to XACC IR
+class StaqToIr : public staq::ast::Visitor {
+public:
+  StaqToIr(const std::string &in_kernelName)
+      : m_kernelName(in_kernelName), m_provider(xacc::getIRProvider("quantum")) {}
+  void visit(VarAccess &) override {}
+  // Expressions
+  void visit(BExpr &) override {}
+  void visit(UExpr &) override {}
+  void visit(PiExpr &) override {}
+  void visit(IntExpr &) override {}
+  void visit(RealExpr &r) override {}
+  void visit(VarExpr &v) override {}
+  void visit(ResetStmt &) override {}
+  void visit(IfStmt &) override {}
+  void visit(BarrierGate &) override {}
+  void visit(GateDecl &) override {}
+  void visit(OracleDecl &) override {}
+  void visit(RegisterDecl &) override {}
+  void visit(AncillaDecl &) override {}
+  void visit(Program &prog) override {
+    // Program body
+    m_runtimeInsts.clear();
+    m_runtimeInsts.reserve(prog.body().size());
+    prog.foreach_stmt([this](auto &stmt) { stmt.accept(*this); });
+  }
+
+  void visit(MeasureStmt &m) override {
+    m_runtimeInsts.emplace_back(
+        std::make_shared<xacc::quantum::Measure>(m.q_arg().offset().value()));
+  }
+
+  void visit(UGate &u) override {
+    m_runtimeInsts.emplace_back(std::make_shared<xacc::quantum::U>(
+        u.arg().offset().value(), u.theta().constant_eval().value(),
+        u.phi().constant_eval().value(), u.lambda().constant_eval().value()));
+  }
+
+  void visit(CNOTGate &cx) override {
+    m_runtimeInsts.emplace_back(std::make_shared<xacc::quantum::CNOT>(
+        cx.ctrl().offset().value(), cx.tgt().offset().value()));
+  }
+
+  void visit(DeclaredGate &g) override {
+    auto xacc_name = staq_to_xacc.at(g.name());
+    // Handle common gates:
+    if (xacc_name == "Rx") {
+      m_runtimeInsts.emplace_back(std::make_shared<xacc::quantum::Rx>(
+          g.qarg(0).offset().value(), g.carg(0).constant_eval().value()));
+    } else if (xacc_name == "Ry") {
+      m_runtimeInsts.emplace_back(std::make_shared<xacc::quantum::Ry>(
+          g.qarg(0).offset().value(), g.carg(0).constant_eval().value()));
+    } else if (xacc_name == "Rz") {
+      m_runtimeInsts.emplace_back(std::make_shared<xacc::quantum::Rz>(
+          g.qarg(0).offset().value(), g.carg(0).constant_eval().value()));
+    } else {
+      // Otherwise, just do generic construction
+      std::vector<std::size_t> gate_bits;
+      std::vector<InstructionParameter> gate_params;
+      for (int i = 0; i < g.num_qargs(); i++) {
+        gate_bits.emplace_back(g.qarg(i).offset().value());
+      }
+      for (int i = 0; i < g.num_cargs(); i++) {
+        gate_params.emplace_back(g.carg(i).constant_eval().value());
+      }
+
+      m_runtimeInsts.emplace_back(
+          m_provider->createInstruction(xacc_name, gate_bits, gate_params));
+    }
+  }
+
+  std::shared_ptr<IR> getIr() {
+    auto composite =
+        xacc::getService<IRProvider>("quantum")->createComposite(m_kernelName);
+    // Since the instructions were *compiled* by staq (valid AST),
+    // hence, we skip all validation.
+    composite->addInstructions(std::move(m_runtimeInsts), false);
+    auto ir = xacc::getService<IRProvider>("quantum")->createIR();
+    ir->addComposite(composite);
+    return ir;
+  }
+
+private:
+  std::vector<InstPtr> m_runtimeInsts;
+  std::shared_ptr<IRProvider> m_provider;
+  std::string m_kernelName;
+};
+
 using namespace xacc::quantum;
 
 class XACCToStaqOpenQasm : public AllGateVisitor {

xacc/ir/CompositeInstruction.hpp

@@ -176,7 +176,7 @@ public:
   virtual void addInstruction(InstPtr instruction) = 0;
   virtual void addInstructions(std::vector<InstPtr> &instruction) = 0;
   virtual void addInstructions(const std::vector<InstPtr> &instruction) = 0;
-  virtual void addInstructions(const std::vector<InstPtr> &&insts) {
+  virtual void addInstructions(const std::vector<InstPtr> &&insts, bool shouldValidate = true) {
     addInstructions(insts);
   }