diff --git a/flang/lib/Lower/CMakeLists.txt b/flang/lib/Lower/CMakeLists.txt
--- a/flang/lib/Lower/CMakeLists.txt
+++ b/flang/lib/Lower/CMakeLists.txt
@@ -8,6 +8,7 @@
   ComplexExpr.cpp
   ConvertType.cpp
   DoLoopHelper.cpp
+  FIRBuilder.cpp
   Mangler.cpp
   OpenMP.cpp
   PFTBuilder.cpp
diff --git a/flang/lib/Lower/FIRBuilder.cpp b/flang/lib/Lower/FIRBuilder.cpp
new file mode 100644
--- /dev/null
+++ b/flang/lib/Lower/FIRBuilder.cpp
@@ -0,0 +1,186 @@
+//===-- FIRBuilder.cpp ----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Lower/FIRBuilder.h"
+#include "SymbolMap.h"
+#include "flang/Lower/Bridge.h"
+#include "flang/Lower/ComplexExpr.h"
+#include "flang/Lower/ConvertType.h"
+#include "flang/Optimizer/Dialect/FIROpsSupport.h"
+#include "flang/Semantics/symbol.h"
+#include "llvm/Support/ErrorHandling.h"
+
+mlir::FuncOp Fortran::lower::FirOpBuilder::createFunction(
+    mlir::Location loc, mlir::ModuleOp module, llvm::StringRef name,
+    mlir::FunctionType ty) {
+  return fir::createFuncOp(loc, module, name, ty);
+}
+
+mlir::FuncOp
+Fortran::lower::FirOpBuilder::getNamedFunction(mlir::ModuleOp modOp,
+                                               llvm::StringRef name) {
+  return modOp.lookupSymbol<mlir::FuncOp>(name);
+}
+
+fir::GlobalOp
+Fortran::lower::FirOpBuilder::getNamedGlobal(mlir::ModuleOp modOp,
+                                             llvm::StringRef name) {
+  return modOp.lookupSymbol<fir::GlobalOp>(name);
+}
+
+mlir::Type Fortran::lower::FirOpBuilder::getRefType(mlir::Type eleTy) {
+  assert(!eleTy.isa<fir::ReferenceType>());
+  return fir::ReferenceType::get(eleTy);
+}
+
+mlir::Value
+Fortran::lower::FirOpBuilder::createNullConstant(mlir::Location loc) {
+  auto indexType = getIndexType();
+  auto zero = createIntegerConstant(loc, indexType, 0);
+  auto noneRefType = getRefType(getNoneType());
+  return createConvert(loc, noneRefType, zero);
+}
+
+mlir::Value Fortran::lower::FirOpBuilder::createIntegerConstant(
+    mlir::Location loc, mlir::Type ty, std::int64_t cst) {
+  return create<mlir::ConstantOp>(loc, ty, getIntegerAttr(ty, cst));
+}
+
+mlir::Value Fortran::lower::FirOpBuilder::createRealConstant(
+    mlir::Location loc, mlir::Type realType, const llvm::APFloat &val) {
+  return create<mlir::ConstantOp>(loc, realType, getFloatAttr(realType, val));
+}
+
+mlir::Value
+Fortran::lower::FirOpBuilder::createRealZeroConstant(mlir::Location loc,
+                                                     mlir::Type realType) {
+  mlir::Attribute attr;
+  if (auto firType = realType.dyn_cast<fir::RealType>()) {
+    attr = getFloatAttr(
+        realType,
+        llvm::APFloat(kindMap.getFloatSemantics(firType.getFKind()), 0));
+  } else { // mlir::FloatType.
+    attr = getZeroAttr(realType);
+  }
+  return create<mlir::ConstantOp>(loc, realType, attr);
+}
+
+mlir::Value Fortran::lower::FirOpBuilder::allocateLocal(
+    mlir::Location loc, mlir::Type ty, llvm::StringRef nm,
+    llvm::ArrayRef<mlir::Value> shape, bool asTarget) {
+  llvm::SmallVector<mlir::Value, 8> indices;
+  auto idxTy = getIndexType();
+  llvm::for_each(shape, [&](mlir::Value sh) {
+    indices.push_back(createConvert(loc, idxTy, sh));
+  });
+  llvm::SmallVector<mlir::NamedAttribute, 2> attrs;
+  if (asTarget)
+    attrs.emplace_back(mlir::Identifier::get("target", getContext()),
+                       getUnitAttr());
+  return create<fir::AllocaOp>(loc, ty, nm, llvm::None, indices, attrs);
+}
+
+/// Create a temporary variable on the stack. Anonymous temporaries have no
+/// `name` value.
+mlir::Value Fortran::lower::FirOpBuilder::createTemporary(
+    mlir::Location loc, mlir::Type type, llvm::StringRef name,
+    llvm::ArrayRef<mlir::Value> shape) {
+  auto insPt = saveInsertionPoint();
+  if (shape.empty())
+    setInsertionPointToStart(getEntryBlock());
+  else
+    setInsertionPointAfter(shape.back().getDefiningOp());
+  assert(!type.isa<fir::ReferenceType>() && "cannot be a reference");
+  auto ae = create<fir::AllocaOp>(loc, type, name, llvm::None, shape);
+  restoreInsertionPoint(insPt);
+  return ae;
+}
+
+/// Create a global variable in the (read-only) data section. A global variable
+/// must have a unique name to identify and reference it.
+fir::GlobalOp Fortran::lower::FirOpBuilder::createGlobal(
+    mlir::Location loc, mlir::Type type, llvm::StringRef name,
+    mlir::StringAttr linkage, mlir::Attribute value, bool isConst) {
+  auto module = getModule();
+  auto insertPt = saveInsertionPoint();
+  if (auto glob = module.lookupSymbol<fir::GlobalOp>(name))
+    return glob;
+  setInsertionPoint(module.getBody()->getTerminator());
+  auto glob = create<fir::GlobalOp>(loc, name, isConst, type, value, linkage);
+  restoreInsertionPoint(insertPt);
+  return glob;
+}
+
+fir::GlobalOp Fortran::lower::FirOpBuilder::createGlobal(
+    mlir::Location loc, mlir::Type type, llvm::StringRef name, bool isConst,
+    std::function<void(FirOpBuilder &)> bodyBuilder, mlir::StringAttr linkage) {
+  auto module = getModule();
+  auto insertPt = saveInsertionPoint();
+  if (auto glob = module.lookupSymbol<fir::GlobalOp>(name))
+    return glob;
+  setInsertionPoint(module.getBody()->getTerminator());
+  auto glob = create<fir::GlobalOp>(loc, name, isConst, type, mlir::Attribute{},
+                                    linkage);
+  auto &region = glob.getRegion();
+  region.push_back(new mlir::Block);
+  auto &block = glob.getRegion().back();
+  setInsertionPointToStart(&block);
+  bodyBuilder(*this);
+  restoreInsertionPoint(insertPt);
+  return glob;
+}
+
+mlir::Value Fortran::lower::FirOpBuilder::convertWithSemantics(
+    mlir::Location loc, mlir::Type toTy, mlir::Value val) {
+  assert(toTy && "store location must be typed");
+  auto fromTy = val.getType();
+  if (fromTy == toTy)
+    return val;
+  // FIXME: add a fir::is_integer() test
+  ComplexExprHelper helper{*this, loc};
+  if ((fir::isa_real(fromTy) || fromTy.isSignlessInteger()) &&
+      fir::isa_complex(toTy)) {
+    // imaginary part is zero
+    auto eleTy = helper.getComplexPartType(toTy);
+    auto cast = createConvert(loc, eleTy, val);
+    llvm::APFloat zero{
+        kindMap.getFloatSemantics(toTy.cast<fir::CplxType>().getFKind()), 0};
+    auto imag = createRealConstant(loc, eleTy, zero);
+    return helper.createComplex(toTy, cast, imag);
+  }
+  // FIXME: add a fir::is_integer() test
+  if (fir::isa_complex(fromTy) &&
+      (toTy.isSignlessInteger() || fir::isa_real(toTy))) {
+    // drop the imaginary part
+    auto rp = helper.extractComplexPart(val, /*isImagPart=*/false);
+    return createConvert(loc, toTy, rp);
+  }
+  return createConvert(loc, toTy, val);
+}
+
+mlir::Value Fortran::lower::FirOpBuilder::createConvert(mlir::Location loc,
+                                                        mlir::Type toTy,
+                                                        mlir::Value val) {
+  if (val.getType() != toTy)
+    return create<fir::ConvertOp>(loc, toTy, val);
+  return val;
+}
+
+fir::StringLitOp Fortran::lower::FirOpBuilder::createStringLit(
+    mlir::Location loc, mlir::Type eleTy, llvm::StringRef data) {
+  auto strAttr = mlir::StringAttr::get(data, getContext());
+  auto valTag = mlir::Identifier::get(fir::StringLitOp::value(), getContext());
+  mlir::NamedAttribute dataAttr(valTag, strAttr);
+  auto sizeTag = mlir::Identifier::get(fir::StringLitOp::size(), getContext());
+  mlir::NamedAttribute sizeAttr(sizeTag, getI64IntegerAttr(data.size()));
+  llvm::SmallVector<mlir::NamedAttribute, 2> attrs{dataAttr, sizeAttr};
+  auto arrTy =
+      fir::SequenceType::get(fir::SequenceType::Shape(1, data.size()), eleTy);
+  return create<fir::StringLitOp>(loc, llvm::ArrayRef<mlir::Type>{arrTy},
+                                  llvm::None, attrs);
+}