Index: flang/include/flang/Optimizer/Support/InternalNames.h
===================================================================
--- /dev/null
+++ flang/include/flang/Optimizer/Support/InternalNames.h
@@ -0,0 +1,127 @@
+//===-- Optimizer/Support/InternalNames.h -----------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef OPTIMIZER_SUPPORT_INTERNALNAMES_H
+#define OPTIMIZER_SUPPORT_INTERNALNAMES_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
+#include <cstdint>
+
+namespace fir {
+
+/// Internal name mangling of identifiers
+///
+/// In order to generate symbolically referencable artifacts in a ModuleOp,
+/// it is required that those symbols be uniqued.  This is a simple interface
+/// for converting Fortran symbols into unique names.
+///
+/// This is intentionally bijective. Given a symbol's parse name, type, and
+/// scope-like information, we can generate a uniqued (mangled) name.  Given a
+/// uniqued name, we can return the symbol parse name, type of the symbol, and
+/// any scope-like information for that symbol.
+struct NameUniquer {
+  enum class IntrinsicType { CHARACTER, COMPLEX, INTEGER, LOGICAL, REAL };
+
+  /// The sort of the unique name
+  enum class NameKind {
+    NOT_UNIQUED,
+    COMMON,
+    CONSTANT,
+    DERIVED_TYPE,
+    DISPATCH_TABLE,
+    GENERATED,
+    INTRINSIC_TYPE_DESC,
+    PROCEDURE,
+    TYPE_DESC,
+    VARIABLE
+  };
+
+  /// Components of an unparsed unique name
+  struct DeconstructedName {
+    DeconstructedName(llvm::StringRef name) : name{name} {}
+    DeconstructedName(llvm::ArrayRef<std::string> modules,
+                      llvm::Optional<std::string> host, llvm::StringRef name,
+                      llvm::ArrayRef<std::int64_t> kinds)
+        : modules{modules.begin(), modules.end()}, host{host}, name{name},
+          kinds{kinds.begin(), kinds.end()} {}
+
+    llvm::SmallVector<std::string, 2> modules;
+    llvm::Optional<std::string> host;
+    std::string name;
+    llvm::SmallVector<std::int64_t, 4> kinds;
+  };
+
+  NameUniquer() = default;
+
+  /// Unique a common block name
+  std::string doCommonBlock(llvm::StringRef name);
+
+  /// Unique a (global) constant name
+  std::string doConstant(llvm::ArrayRef<llvm::StringRef> modules,
+                         llvm::StringRef name);
+
+  /// Unique a dispatch table name
+  std::string doDispatchTable(llvm::ArrayRef<llvm::StringRef> modules,
+                              llvm::Optional<llvm::StringRef> host,
+                              llvm::StringRef name,
+                              llvm::ArrayRef<std::int64_t> kinds);
+
+  /// Unique a compiler generated name
+  std::string doGenerated(llvm::StringRef name);
+
+  /// Unique an intrinsic type descriptor
+  std::string doIntrinsicTypeDescriptor(llvm::ArrayRef<llvm::StringRef> modules,
+                                        llvm::Optional<llvm::StringRef> host,
+                                        IntrinsicType type, std::int64_t kind);
+
+  /// Unique a procedure name
+  std::string doProcedure(llvm::ArrayRef<llvm::StringRef> modules,
+                          llvm::Optional<llvm::StringRef> host,
+                          llvm::StringRef name);
+
+  /// Unique a derived type name
+  std::string doType(llvm::ArrayRef<llvm::StringRef> modules,
+                     llvm::Optional<llvm::StringRef> host, llvm::StringRef name,
+                     llvm::ArrayRef<std::int64_t> kinds);
+
+  /// Unique a (derived) type descriptor name
+  std::string doTypeDescriptor(llvm::ArrayRef<llvm::StringRef> modules,
+                               llvm::Optional<llvm::StringRef> host,
+                               llvm::StringRef name,
+                               llvm::ArrayRef<std::int64_t> kinds);
+  std::string doTypeDescriptor(llvm::ArrayRef<std::string> modules,
+                               llvm::Optional<std::string> host,
+                               llvm::StringRef name,
+                               llvm::ArrayRef<std::int64_t> kinds);
+
+  /// Unique a (global) variable name. A variable with save attribute
+  /// defined inside a subprogram also needs to be handled here
+  std::string doVariable(llvm::ArrayRef<llvm::StringRef> modules,
+                         llvm::Optional<llvm::StringRef> host,
+                         llvm::StringRef name);
+
+  /// Entry point for the PROGRAM (called by the runtime)
+  /// Can be overridden with the `--main-entry-name=<name>` option.
+  static llvm::StringRef doProgramEntry();
+
+  /// Decompose `uniquedName` into the parse name, symbol type, and scope info
+  static std::pair<NameKind, DeconstructedName>
+  deconstruct(llvm::StringRef uniquedName);
+
+private:
+  std::string intAsString(std::int64_t i);
+  std::string doKind(std::int64_t kind);
+  std::string doKinds(llvm::ArrayRef<std::int64_t> kinds);
+  std::string toLower(llvm::StringRef name);
+};
+
+} // namespace fir
+
+#endif // OPTIMIZER_SUPPORT_INTERNALNAMES_H
Index: flang/lib/Optimizer/Support/CMakeLists.txt
===================================================================
--- flang/lib/Optimizer/Support/CMakeLists.txt
+++ flang/lib/Optimizer/Support/CMakeLists.txt
@@ -1,6 +1,7 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 
 add_flang_library(FIRSupport
+  InternalNames.cpp
   KindMapping.cpp
 
   DEPENDS
Index: flang/lib/Optimizer/Support/InternalNames.cpp
===================================================================
--- /dev/null
+++ flang/lib/Optimizer/Support/InternalNames.cpp
@@ -0,0 +1,274 @@
+//===-- InternalNames.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/Optimizer/Support/InternalNames.h"
+#include "mlir/IR/Diagnostics.h"
+#include "llvm/Support/CommandLine.h"
+
+static llvm::cl::opt<std::string> mainEntryName(
+    "main-entry-name",
+    llvm::cl::desc("override the name of the default PROGRAM entry (may be "
+                   "helpful for using other runtimes)"));
+
+constexpr std::int64_t BAD_VALUE = -1;
+
+inline std::string prefix() { return "_Q"; }
+
+static std::string doModules(llvm::ArrayRef<llvm::StringRef> mods) {
+  std::string result;
+  auto *token = "M";
+  for (auto mod : mods) {
+    result.append(token).append(mod);
+    token = "S";
+  }
+  return result;
+}
+
+static std::string doModulesHost(llvm::ArrayRef<llvm::StringRef> mods,
+                                 llvm::Optional<llvm::StringRef> host) {
+  std::string result = doModules(mods);
+  if (host.hasValue())
+    result.append("F").append(*host);
+  return result;
+}
+
+inline llvm::SmallVector<llvm::StringRef, 2>
+convertToStringRef(llvm::ArrayRef<std::string> from) {
+  return {from.begin(), from.end()};
+}
+
+inline llvm::Optional<llvm::StringRef>
+convertToStringRef(const llvm::Optional<std::string> &from) {
+  llvm::Optional<llvm::StringRef> to;
+  if (from.hasValue())
+    to = from.getValue();
+  return to;
+}
+
+static std::string readName(llvm::StringRef uniq, std::size_t &i,
+                            std::size_t init, std::size_t end) {
+  for (i = init; i < end && uniq[i] >= 'a' && uniq[i] <= 'z'; ++i) {
+    // do nothing
+  }
+  return uniq.substr(init, i).str();
+}
+
+static std::int64_t readInt(llvm::StringRef uniq, std::size_t &i,
+                            std::size_t init, std::size_t end) {
+  for (i = init; i < end && uniq[i] >= '0' && uniq[i] <= '9'; ++i) {
+    // do nothing
+  }
+  std::int64_t result = BAD_VALUE;
+  if (uniq.substr(init, i).getAsInteger(10, result))
+    return BAD_VALUE;
+  return result;
+}
+
+std::string fir::NameUniquer::toLower(llvm::StringRef name) {
+  return name.lower();
+}
+
+std::string fir::NameUniquer::intAsString(std::int64_t i) {
+  assert(i >= 0);
+  return std::to_string(i);
+}
+
+std::string fir::NameUniquer::doKind(std::int64_t kind) {
+  std::string result = "K";
+  if (kind < 0)
+    return result.append("N").append(intAsString(-kind));
+  return result.append(intAsString(kind));
+}
+
+std::string fir::NameUniquer::doKinds(llvm::ArrayRef<std::int64_t> kinds) {
+  std::string result;
+  for (auto i : kinds)
+    result.append(doKind(i));
+  return result;
+}
+
+std::string fir::NameUniquer::doCommonBlock(llvm::StringRef name) {
+  std::string result = prefix();
+  return result.append("B").append(toLower(name));
+}
+
+std::string
+fir::NameUniquer::doConstant(llvm::ArrayRef<llvm::StringRef> modules,
+                             llvm::StringRef name) {
+  std::string result = prefix();
+  return result.append(doModules(modules)).append("EC").append(toLower(name));
+}
+
+std::string
+fir::NameUniquer::doDispatchTable(llvm::ArrayRef<llvm::StringRef> modules,
+                                  llvm::Optional<llvm::StringRef> host,
+                                  llvm::StringRef name,
+                                  llvm::ArrayRef<std::int64_t> kinds) {
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("DT");
+  return result.append(toLower(name)).append(doKinds(kinds));
+}
+
+std::string fir::NameUniquer::doGenerated(llvm::StringRef name) {
+  std::string result = prefix();
+  return result.append("Q").append(name);
+}
+
+std::string fir::NameUniquer::doIntrinsicTypeDescriptor(
+    llvm::ArrayRef<llvm::StringRef> modules,
+    llvm::Optional<llvm::StringRef> host, IntrinsicType type,
+    std::int64_t kind) {
+  const char *name = nullptr;
+  switch (type) {
+  case IntrinsicType::CHARACTER:
+    name = "character";
+    break;
+  case IntrinsicType::COMPLEX:
+    name = "complex";
+    break;
+  case IntrinsicType::INTEGER:
+    name = "integer";
+    break;
+  case IntrinsicType::LOGICAL:
+    name = "logical";
+    break;
+  case IntrinsicType::REAL:
+    name = "real";
+    break;
+  }
+  assert(name && "unknown intrinsic type");
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("C");
+  return result.append(name).append(doKind(kind));
+}
+
+std::string
+fir::NameUniquer::doProcedure(llvm::ArrayRef<llvm::StringRef> modules,
+                              llvm::Optional<llvm::StringRef> host,
+                              llvm::StringRef name) {
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("P");
+  return result.append(toLower(name));
+}
+
+std::string fir::NameUniquer::doType(llvm::ArrayRef<llvm::StringRef> modules,
+                                     llvm::Optional<llvm::StringRef> host,
+                                     llvm::StringRef name,
+                                     llvm::ArrayRef<std::int64_t> kinds) {
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("T");
+  return result.append(toLower(name)).append(doKinds(kinds));
+}
+
+std::string
+fir::NameUniquer::doTypeDescriptor(llvm::ArrayRef<llvm::StringRef> modules,
+                                   llvm::Optional<llvm::StringRef> host,
+                                   llvm::StringRef name,
+                                   llvm::ArrayRef<std::int64_t> kinds) {
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("CT");
+  return result.append(toLower(name)).append(doKinds(kinds));
+}
+
+std::string fir::NameUniquer::doTypeDescriptor(
+    llvm::ArrayRef<std::string> modules, llvm::Optional<std::string> host,
+    llvm::StringRef name, llvm::ArrayRef<std::int64_t> kinds) {
+  auto rmodules = convertToStringRef(modules);
+  auto rhost = convertToStringRef(host);
+  return doTypeDescriptor(rmodules, rhost, name, kinds);
+}
+
+std::string
+fir::NameUniquer::doVariable(llvm::ArrayRef<llvm::StringRef> modules,
+                             llvm::Optional<llvm::StringRef> host,
+                             llvm::StringRef name) {
+  std::string result = prefix();
+  result.append(doModulesHost(modules, host)).append("E");
+  return result.append(toLower(name));
+}
+
+llvm::StringRef fir::NameUniquer::doProgramEntry() {
+  if (mainEntryName.size())
+    return mainEntryName;
+  return "_QQmain";
+}
+
+std::pair<fir::NameUniquer::NameKind, fir::NameUniquer::DeconstructedName>
+fir::NameUniquer::deconstruct(llvm::StringRef uniq) {
+  if (uniq.startswith("_Q")) {
+    llvm::SmallVector<std::string, 4> modules;
+    llvm::Optional<std::string> host;
+    std::string name;
+    llvm::SmallVector<std::int64_t, 8> kinds;
+    NameKind nk = NameKind::NOT_UNIQUED;
+    for (std::size_t i = 2, end{uniq.size()}; i != end;) {
+      switch (uniq[i]) {
+      case 'B':
+        nk = NameKind::COMMON;
+        name = readName(uniq, i, i + 1, end);
+        break;
+      case 'C':
+        if (uniq[i + 1] == 'T') {
+          nk = NameKind::TYPE_DESC;
+          name = readName(uniq, i, i + 2, end);
+        } else {
+          nk = NameKind::INTRINSIC_TYPE_DESC;
+          name = readName(uniq, i, i + 1, end);
+        }
+        break;
+      case 'D':
+        nk = NameKind::DISPATCH_TABLE;
+        assert(uniq[i + 1] == 'T');
+        name = readName(uniq, i, i + 2, end);
+        break;
+      case 'E':
+        if (uniq[i + 1] == 'C') {
+          nk = NameKind::CONSTANT;
+          name = readName(uniq, i, i + 2, end);
+        } else {
+          nk = NameKind::VARIABLE;
+          name = readName(uniq, i, i + 1, end);
+        }
+        break;
+      case 'P':
+        nk = NameKind::PROCEDURE;
+        name = readName(uniq, i, i + 1, end);
+        break;
+      case 'Q':
+        nk = NameKind::GENERATED;
+        name = uniq;
+        i = end;
+        break;
+      case 'T':
+        nk = NameKind::DERIVED_TYPE;
+        name = readName(uniq, i, i + 1, end);
+        break;
+
+      case 'M':
+      case 'S':
+        modules.push_back(readName(uniq, i, i + 1, end));
+        break;
+      case 'F':
+        host = readName(uniq, i, i + 1, end);
+        break;
+      case 'K':
+        if (uniq[i + 1] == 'N')
+          kinds.push_back(-readInt(uniq, i, i + 2, end));
+        else
+          kinds.push_back(readInt(uniq, i, i + 1, end));
+        break;
+
+      default:
+        assert(false && "unknown uniquing code");
+        break;
+      }
+    }
+    return {nk, DeconstructedName(modules, host, name, kinds)};
+  }
+  return {NameKind::NOT_UNIQUED, DeconstructedName(uniq)};
+}