[flang][driver] Delete f18 (i.e. the old Flang driver)

This patch removes `f18`, a.k.a. the old driver. It is being replaced
with the new driver, `flang-new`, which has reached feature parity with
`f18` a while ago. This was discussed in [1] and also in [2].

With this change, `FLANG_BUILD_NEW_DRIVER` is no longer needed and is
also deleted. This means that we are making the dependency on Clang permanent
(i.e. it cannot be disabled with a CMake flag).

LIT set-up is updated accordingly. All references to `f18` or `f18.cpp`
are either updated or removed.

The `F18_FC` variable from the `flang` bash script is replaced with
`FLANG_FC`. The former is still supported for backwards compatibility.

[1] https://lists.llvm.org/pipermail/flang-dev/2021-June/000742.html
[2] https://reviews.llvm.org/D103177

Differential Revision: https://reviews.llvm.org/D105811

Author: banach-space

flang/CMakeLists.txt

@@ -26,11 +26,6 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(Flang)
   set(FLANG_STANDALONE_BUILD ON)
 
-  # For in-tree builds, this variable is inherited from
-  # llvm-project/llvm/CMakeLists.txt. For out-of-tree builds, we need a
-  # separate definition.
-  option(FLANG_BUILD_NEW_DRIVER "Build the flang compiler driver" ON)
-
   set(FLANG_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
   if (NOT MSVC_IDE)
     set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
@@ -46,24 +41,22 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   get_filename_component(LLVM_DIR_ABSOLUTE ${LLVM_DIR} REALPATH)
   list(APPEND CMAKE_MODULE_PATH ${LLVM_DIR_ABSOLUTE})
 
-  if(FLANG_BUILD_NEW_DRIVER)
-    # Users might specify a path to CLANG_DIR that's:
-    #   * a full path, or
-    #   * a path relative to the path of this script.
-    # Append the absolute path to CLANG_DIR so that find_package works in both
-    # cases.
-    get_filename_component(
-      CLANG_DIR_ABSOLUTE
-      ${CLANG_DIR}
-      REALPATH
-      ${CMAKE_CURRENT_SOURCE_DIR})
-    list(APPEND CMAKE_MODULE_PATH ${CLANG_DIR_ABSOLUTE})
-
-    # TODO: Remove when libclangDriver is lifted out of Clang
-    find_package(Clang REQUIRED PATHS "${CLANG_DIR_ABSOLUTE}" NO_DEFAULT_PATH)
-    if (NOT Clang_FOUND)
-      message(FATAL_ERROR "Failed to find Clang")
-    endif()
+  # Users might specify a path to CLANG_DIR that's:
+  #   * a full path, or
+  #   * a path relative to the path of this script.
+  # Append the absolute path to CLANG_DIR so that find_package works in both
+  # cases.
+  get_filename_component(
+    CLANG_DIR_ABSOLUTE
+    ${CLANG_DIR}
+    REALPATH
+    ${CMAKE_CURRENT_SOURCE_DIR})
+  list(APPEND CMAKE_MODULE_PATH ${CLANG_DIR_ABSOLUTE})
+
+  # TODO: Remove when libclangDriver is lifted out of Clang
+  find_package(Clang REQUIRED PATHS "${CLANG_DIR_ABSOLUTE}" NO_DEFAULT_PATH)
+  if (NOT Clang_FOUND)
+    message(FATAL_ERROR "Failed to find Clang")
   endif()
 
   # If LLVM links to zlib we need the imported targets so we can too.
@@ -80,9 +73,7 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   include(HandleLLVMOptions)
   include(VersionFromVCS)
 
-  if(FLANG_BUILD_NEW_DRIVER)
-    include(AddClang)
-  endif()
+  include(AddClang)
 
   include(TableGen)
   find_package(MLIR REQUIRED CONFIG)
@@ -206,20 +197,18 @@ endif()
 set(FLANG_INTRINSIC_MODULES_DIR ${CMAKE_BINARY_DIR}/include/flang)
 set(FLANG_INCLUDE_DIR ${FLANG_BINARY_DIR}/include)
 
-if(FLANG_BUILD_NEW_DRIVER)
-    # TODO: Remove when libclangDriver is lifted out of Clang
-    if(FLANG_STANDALONE_BUILD)
-      set(CLANG_INCLUDE_DIR ${CLANG_INCLUDE_DIRS} )
-      # No need to specify TableGen output dir as that's embedded in CLANG_DIR
-    else()
-      set(CLANG_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/../clang/include )
-      # Specify TableGen output dir for things like DiagnosticCommonKinds.inc,
-      # DiagnosticDriverKinds.inc (required for reporting diagnostics)
-      set(CLANG_TABLEGEN_OUTPUT_DIR ${CMAKE_BINARY_DIR}/tools/clang/include)
-      include_directories(SYSTEM ${CLANG_TABLEGEN_OUTPUT_DIR})
-    endif()
-    include_directories(SYSTEM ${CLANG_INCLUDE_DIR})
+# TODO: Remove when libclangDriver is lifted out of Clang
+if(FLANG_STANDALONE_BUILD)
+  set(CLANG_INCLUDE_DIR ${CLANG_INCLUDE_DIRS} )
+  # No need to specify TableGen output dir as that's embedded in CLANG_DIR
+else()
+  set(CLANG_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/../clang/include )
+  # Specify TableGen output dir for things like DiagnosticCommonKinds.inc,
+  # DiagnosticDriverKinds.inc (required for reporting diagnostics)
+  set(CLANG_TABLEGEN_OUTPUT_DIR ${CMAKE_BINARY_DIR}/tools/clang/include)
+  include_directories(SYSTEM ${CLANG_TABLEGEN_OUTPUT_DIR})
 endif()
+include_directories(SYSTEM ${CLANG_INCLUDE_DIR})
 
 # tco tool and FIR lib output directories
 if(FLANG_STANDALONE_BUILD)

flang/docs/ImplementingASemanticCheck.md

@@ -12,7 +12,7 @@
    :local:
 ```
 
-I recently added a semantic check to the f18 compiler front end.  This document
+I recently added a semantic check to the Flang compiler front end.  This document
 describes my thought process and the resulting implementation.
 
 For more information about the compiler, start with the 
@@ -67,7 +67,7 @@ of the call to `intentOutFunc()`:
 
 I also used this program to produce a parse tree for the program using the command:
 ```bash
-  f18 -fdebug-dump-parse-tree -fsyntax-only testfun.f90
+  flang-new -fc1 -fdebug-dump-parse-tree testfun.f90
 ```
 
 Here's the relevant fragment of the parse tree produced by the compiler:
@@ -295,7 +295,7 @@ In `lib/Semantics/check-do.cpp`, I added an (almost empty) implementation:
 I then built the compiler with these changes and ran it on my test program.
 This time, I made sure to invoke semantic checking.  Here's the command I used:
 ```bash
-  f18 -fdebug-resolve-names -fdebug-dump-parse-tree -funparse-with-symbols testfun.f90
+  flang-new -fc1 -fdebug-unparse-with-symbols testfun.f90
 ```
 
 This produced the output:
@@ -361,7 +361,7 @@ I noted that a `SymbolSet` did not actually contain an
 full `semantics::Symbol` objects into the set.  Ideally, we would be able to create an
 `std::set<Symbol &>` (a set of C++ references to symbols).  But C++ doesn't
 support sets that contain references.  This limitation is part of the rationale
-for the f18 implementation of type `common::Reference`, which is defined in
+for the Flang implementation of type `common::Reference`, which is defined in
   `include/flang/Common/reference.h`.
 
 `SymbolRef`, the specialization of the template `common::Reference` for

flang/docs/Overview.md

@@ -6,6 +6,11 @@
   
 -->
 
+# Intro
+This document goes briefly over compiler phases in Flang. It focuses on the
+internal implementation and as such, it is intended for Flang developers rather
+than end-users.
+
 # Overview of Compiler Phases
 
 ```eval_rst
@@ -33,7 +38,7 @@ See: [Preprocessing.md](Preprocessing.md).
 
 **Entry point:** `parser::Parsing::Prescan`
 
-**Command:** `f18 -E src.f90` dumps the cooked character stream
+**Command:** `flang-new -fc1 -E src.f90` dumps the cooked character stream
 
 ## Parse
 
@@ -46,8 +51,8 @@ See: [Preprocessing.md](Preprocessing.md).
 **Entry point:** `parser::Parsing::Parse`
 
 **Command:**
-  - `f18 -fdebug-dump-parse-tree -fsyntax-only src.f90` dumps the parse tree
-  - `f18 -funparse src.f90` converts the parse tree to normalized Fortran
+  - `flang-new -fc1 -fdebug-dump-parse-tree src.f90` dumps the parse tree
+  - `flang-new -fc1 -fdebug-unparse src.f90` converts the parse tree to normalized Fortran
 
 ## Validate Labels and Canonicalize Do Statements
 
@@ -74,7 +79,7 @@ See: [Preprocessing.md](Preprocessing.md).
 
 **Entry points:** `semantics::ResolveNames`, `semantics::RewriteParseTree`
 
-**Command:** `f18 -fdebug-dump-symbols -fsyntax-only src.f90` dumps the
+**Command:** `flang-new -fc1 -fdebug-dump-symbols src.f90` dumps the
   tree of scopes and symbols in each scope
 
 ## Check DO CONCURRENT Constraints

flang/include/flang/Frontend/CompilerInvocation.h

@@ -184,8 +184,7 @@ class CompilerInvocation : public CompilerInvocationBase {
     useAnalyzedObjectsForUnparse_ = flag;
   }
 
-  /// Set the Fortran options to predifined defaults. These defaults are
-  /// consistend with f18/f18.cpp.
+  /// Set the Fortran options to predefined defaults.
   // TODO: We should map frontendOpts_ to parserOpts_ instead. For that, we
   // need to extend frontendOpts_ first. Next, we need to add the corresponding
   // compiler driver options in libclangDriver.

flang/include/flang/Frontend/FrontendOptions.h

@@ -87,10 +87,6 @@ enum ActionKind {
 /// \return True if the file extension should be processed as fixed form
 bool isFixedFormSuffix(llvm::StringRef suffix);
 
-// TODO: Find a more suitable location for this. Added for compability with
-// f18.cpp (this is equivalent to `asFortran` defined there).
-Fortran::parser::AnalyzedObjectsAsFortran getBasicAsFortran();
-
 /// \param suffix The file extension
 /// \return True if the file extension should be processed as free form
 bool isFreeFormSuffix(llvm::StringRef suffix);

flang/lib/CMakeLists.txt

@@ -4,10 +4,7 @@ add_subdirectory(Decimal)
 add_subdirectory(Lower)
 add_subdirectory(Parser)
 add_subdirectory(Semantics)
-
-if(FLANG_BUILD_NEW_DRIVER)
-  add_subdirectory(Frontend)
-  add_subdirectory(FrontendTool)
-endif()
+add_subdirectory(Frontend)
+add_subdirectory(FrontendTool)
 
 add_subdirectory(Optimizer)

flang/lib/Frontend/CompilerInvocation.cpp

@@ -571,7 +571,6 @@ void CompilerInvocation::collectMacroDefinitions() {
 void CompilerInvocation::SetDefaultFortranOpts() {
   auto &fortranOptions = fortranOpts();
 
-  // These defaults are based on the defaults in f18/f18.cpp.
   std::vector<std::string> searchDirectories{"."s};
   fortranOptions.searchDirectories = searchDirectories;
   fortranOptions.isFixedForm = false;

flang/test/CMakeLists.txt

@@ -32,13 +32,9 @@ set(FLANG_TEST_PARAMS
   flang_site_config=${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py)
 
 set(FLANG_TEST_DEPENDS
-  f18 FileCheck count not module_files fir-opt tco
+  flang-new FileCheck count not module_files fir-opt tco
 )
 
-if (FLANG_BUILD_NEW_DRIVER)
-  list(APPEND FLANG_TEST_DEPENDS flang-new)
-endif()
-
 if (FLANG_INCLUDE_TESTS)
   if (FLANG_GTEST_AVAIL)
     list(APPEND FLANG_TEST_DEPENDS FlangUnitTests)

flang/test/Driver/help-f18.f90

@@ -40,10 +40,7 @@
 
 # If the new Flang driver is enabled, add the corresponding feature to
 # config.
-if config.include_flang_new_driver_test:
-  config.available_features.add('new-flang-driver')
-else:
-  config.available_features.add('old-flang-driver')
+config.available_features.add('new-flang-driver')
 
 # test_source_root: The root path where tests are located.
 config.test_source_root = os.path.dirname(__file__)
@@ -64,16 +61,10 @@
 
 # For each occurrence of a flang tool name, replace it with the full path to
 # the build directory holding that tool.
-tools = []
-if config.include_flang_new_driver_test:
-   tools.append(ToolSubst('%flang', command=FindTool('flang-new'), unresolved='fatal'))
-   tools.append(ToolSubst('%flang_fc1', command=FindTool('flang-new'),
-    extra_args=['-fc1'], unresolved='fatal'))
-else:
-   tools.append(ToolSubst('%flang', command=FindTool('f18'),
-    unresolved='fatal'))
-   tools.append(ToolSubst('%flang_fc1', command=FindTool('f18'),
-    unresolved='fatal'))
+tools = [
+        ToolSubst('%flang', command=FindTool('flang-new'), unresolved='fatal'),
+    ToolSubst('%flang_fc1', command=FindTool('flang-new'), extra_args=['-fc1'],
+        unresolved='fatal')]
 
 # Define some variables to help us test that the flang runtime doesn't depend on
 # the C++ runtime libraries. For this we need a C compiler. If for some reason