LLVMFlang: Add support for LLVM Flang

LLVM Flang (https://github.com/llvm/llvm-project/tree/main/flang) is an LLVM
Fortran compiler that shares the same name as Flang (also known as Classic
Flang). Classic Flang is in active development and is already identified by
CMake as Flang. As such, LLVM Flang will be identified as `LLVMFlang`.

Fixes: #22387

5 files changed, 29 insertions, 1 deletions

diff --git a/Help/release/dev/LLVMFlang-compiler.rst b/Help/release/dev/LLVMFlang-compiler.rst
new file mode 100644
index 0000000000..1d29449028
--- /dev/null
+++ b/Help/release/dev/LLVMFlang-compiler.rst
@@ -0,0 +1,6 @@
+LLVMFlang-compiler
+------------------
+
+* LLVM's `flang`_ Fortran compiler is now supported, with compiler id ``LLVMFlang``.
+
+.. _`flang`: https://github.com/llvm/llvm-project/tree/main/flang
diff --git a/Help/variable/CMAKE_LANG_COMPILER_ID.rst b/Help/variable/CMAKE_LANG_COMPILER_ID.rst
index cd7d5cdaea..6a0a1d9cd4 100644
--- a/Help/variable/CMAKE_LANG_COMPILER_ID.rst
+++ b/Help/variable/CMAKE_LANG_COMPILER_ID.rst
@@ -18,7 +18,8 @@ include:
   Clang = LLVM Clang (clang.llvm.org)
   Cray = Cray Compiler (cray.com)
   Embarcadero, Borland = Embarcadero (embarcadero.com)
-  Flang = Flang LLVM Fortran Compiler
+  Flang = Classic Flang Fortran Compiler (https://github.com/flang-compiler/flang)
+  LLVMFlang = LLVM Flang Fortran Compiler (https://github.com/llvm/llvm-project/tree/main/flang)
   Fujitsu = Fujitsu HPC compiler (Trad mode)
   FujitsuClang = Fujitsu HPC compiler (Clang mode)
   G95 = G95 Fortran (g95.org)
diff --git a/Modules/CMakeDetermineFortranCompiler.cmake b/Modules/CMakeDetermineFortranCompiler.cmake
index 1c4b6eaa55..650c87a707 100644
--- a/Modules/CMakeDetermineFortranCompiler.cmake
+++ b/Modules/CMakeDetermineFortranCompiler.cmake
@@ -91,6 +91,7 @@ else()
       set(_Fortran_COMPILER_NAMES_Absoft    af95 af90 af77)
       set(_Fortran_COMPILER_NAMES_PGI       pgf95 pgfortran pgf90 pgf77)
       set(_Fortran_COMPILER_NAMES_Flang     flang)
+      set(_Fortran_COMPILER_NAMES_LLVMFlang flang)
       set(_Fortran_COMPILER_NAMES_PathScale pathf2003 pathf95 pathf90)
       set(_Fortran_COMPILER_NAMES_XL        xlf)
       set(_Fortran_COMPILER_NAMES_VisualAge xlf95 xlf90 xlf)
diff --git a/Modules/CMakeFortranCompilerId.F.in b/Modules/CMakeFortranCompilerId.F.in
index 969c8414c3..f5c2ab55df 100644
--- a/Modules/CMakeFortranCompilerId.F.in
+++ b/Modules/CMakeFortranCompilerId.F.in
@@ -154,6 +154,13 @@
 # if defined(__FLANG_PATCHLEVEL__)
 #  define COMPILER_VERSION_PATCH DEC(__FLANG_PATCHLEVEL__)
 # endif
+#elif defined(__flang__)
+        PRINT *, 'INFO:compiler[LLVMFlang]'
+# define COMPILER_VERSION_MAJOR DEC(__flang_major__)
+# define COMPILER_VERSION_MINOR DEC(__flang_minor__)
+# if defined(__flang_patchlevel__)
+#  define COMPILER_VERSION_PATCH DEC(__flang_patchlevel__)
+# endif
 #elif defined(_AIX) || defined(__AIX) || defined(__AIX__) || defined(__aix) || defined(__aix__)
         PRINT *, 'INFO:compiler[VisualAge]'
 #elif defined(__hpux) || defined(__hpux__)
diff --git a/Modules/Compiler/LLVMFlang-Fortran.cmake b/Modules/Compiler/LLVMFlang-Fortran.cmake
new file mode 100644
index 0000000000..7e9ba5ecb7
--- /dev/null
+++ b/Modules/Compiler/LLVMFlang-Fortran.cmake
@@ -0,0 +1,13 @@
+set(CMAKE_Fortran_SUBMODULE_SEP "-")
+set(CMAKE_Fortran_SUBMODULE_EXT ".mod")
+
+set(CMAKE_Fortran_PREPROCESS_SOURCE
+    "<CMAKE_Fortran_COMPILER> -cpp <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
+
+set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")
+set(CMAKE_Fortran_FORMAT_FREE_FLAG "-ffree-form")
+
+set(CMAKE_Fortran_MODDIR_FLAG "-module-dir")
+
+set(CMAKE_Fortran_COMPILE_OPTIONS_PREPROCESS_ON "-cpp")
+set(CMAKE_Fortran_COMPILE_OPTIONS_PREPROCESS_OFF "-nocpp")