[gn build] Create abi-breaking.h, config.h, llvm-config.h, and add a build file for llvm/lib/Support.

[thakis]

Summary

The comments at the top of llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn and llvm/utils/gn/build/write_cmake_config.py should explain the main bits happening in this patch. The main parts here are that these headers are generated at build time, not gn time, and that currently they don't do any actual feature checks but just hardcode most things based on the current OS, which seems to work well enough. If this stops being enough, the feature checks should each be their own action writing the result to somewhere, and the config write step should depend on those checks (so that they can run in parallel and as part of the build) -- utils/llvm/gn/README.rst already has some more words on that in "Philosophy".

(write_cmake_config.py is also going to be used to write clang's clang/include/clang/Config/config.h)

This also adds a few files for linking to system libraries in a consistent way if needed in llvm/utils/gn/build/libs (and moves pthread to that model). This might be overkill; I'm not married to that part (but I kind of like it).

I'm also adding llvm/utils/gn/secondary/llvm/lib/Target/targets.gni in this patch because $native_arch is needed for writing llvm-config.h -- the rest of it will be used later, when the build files for llvm/lib/Target get added. That file describes how to select which archs to build.

As a demo, also add a build file for llvm-undname and make it the default build target (it depends on everything that can currently be built).

[thakis]

fix a comment

[phosek]

llvm/utils/gn/build/libs/zlib/enable.gni

2

Shouldn't this be an arg as well? It's an option today and various builds disable it.

llvm/utils/gn/build/write_cmake_config.py

49

Can you pass the documentation above as description and epilog to the ArgumentParser so it gets printed out with --help?

50

Shouldn't this be just a positional argument?

51

Would it be possible to add description for all arguments?

52

What if this argument is unset?

63

Make it a global constant?

65

Wrap in with statement so it gets closed automatically.

103

Ditto

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

44

This whole block seems unused.

llvm/utils/gn/secondary/llvm/triples.gni

11

Definitely, we always set host triple to x86_64-linux-gnu in our build (because nobody has time to type unknown)

[thakis]

Thanks for the review! Implemented most suggestions.

llvm/utils/gn/build/libs/zlib/enable.gni

2

Done. I agree it should match llvm_enable_libxml2 which I did make a declare_arg. I actually think it'd make more sense to say "llvm requires libxml2 and zlib on non-Win" instead of dynamically disabling features, but probably makes sense to match cmake.

Out of interest, do builds you care about disable this?

llvm/utils/gn/build/write_cmake_config.py

50

Is there some guideline what to use for what? Changed; I had it the current way because I found the command easier to read when looking at it with ninja -v.

52

Made it required.

63

Why? It's only used here.

65

It's a short and short-running script, the string will be garbage-collected, and I don't need to indent everything 4 more (or introduce a function that's called from just one place.

103

This is for consistency with the previous place :-)

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

44

From the phab description: "I'm also adding llvm/utils/gn/secondary/llvm/lib/Target/targets.gni in this patch because $native_arch is needed for writing llvm-config.h -- the rest of it will be used later, when the build files for llvm/lib/Target get added. That file describes how to select which archs to build."

Want me to defer adding the bits I need later until I need them?

[phosek]

Few more nits, but otherwise LGTM.

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

34

Move this assert into an else branch below? That way you don't have repeat all targets here and in the if conditions below.

44

I missed that part, I guess this is fine then.

53

Could you also add an error message to make it more clear what's wrong?

[thakis]

Thanks! Landing.

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

34

Much nicer, thanks!

llvm/utils/gn/README.rst

 
 GN has extensive built-in help; try e.g. `gn help gen` to see the help
 for the `gen` command. The full GN reference is also `available online
 <https://gn.googlesource.com/gn/+/master/docs/reference.md>`_.
 
 GN has an autoformatter: `git ls-files '*.gn' '*.gni' | xargs -n 1 gn format`
 after making GN build changes is your friend.
 
-To not put `BUILD.gn` into the main tree, they are all below `utils/gn/tree`.
-For example, the build file for `llvm/lib/Support` is in
-`utils/gn/tree/llvm/lib/Support`.
+To not put `BUILD.gn` into the main tree, they are all below
+`utils/gn/secondary`.  For example, the build file for `llvm/lib/Support` is in
+`utils/gn/secondary/llvm/lib/Support`.
 
 .. _Philosophy:
 
 Philosophy
 ==========
 
 GN believes in using GN arguments to configure the build explicitly, instead
 of implicitly figuring out what to do based on what's available on the current

llvm/utils/gn/build/BUILD.gn

 import("//llvm/utils/gn/build/buildflags.gni")
 import("//llvm/utils/gn/build/mac_sdk.gni")
 import("//llvm/utils/gn/build/toolchain/compiler.gni")
-import("//llvm/utils/gn/build/enable_threads.gni")
 
 config("compiler_defaults") {
   # FIXME: Don't define this globally here.
   if (host_os != "win") {
     defines = [ "LLVM_ON_UNIX" ]
   }
 
   if (!llvm_enable_assertions) {
config("clang_code") {
   ]
 }
 
 config("warn_covered_switch_default") {
   if (is_clang) {
     cflags = [ "-Wcovered-switch-default" ]
   }
 }
-
-config("pthread_config") {
-  visibility = [ ":pthread" ]
-  libs = [ "pthread" ]
-}
-
-group("pthread") {
-  if (llvm_enable_threads && host_os != "win") {
-    public_configs = [ ":pthread_config" ]
-  }
-}

llvm/utils/gn/build/libs/pthread/BUILD.gn

+import("//llvm/utils/gn/build/libs/pthread/enable.gni")
+
+config("pthread_config") {
+  visibility = [ ":pthread" ]
+  libs = [ "pthread" ]
+}
+
+group("pthread") {
+  if (llvm_enable_threads && host_os != "win") {
+    public_configs = [ ":pthread_config" ]
+  }
+}

llvm/utils/gn/build/libs/terminfo/BUILD.gn

+import("//llvm/utils/gn/build/libs/terminfo/enable.gni")
+
+config("terminfo_config") {
+  visibility = [ ":terminfo" ]
+  libs = [ "ncurses" ]
+}
+
+group("terminfo") {
+  if (llvm_enable_terminfo) {
+    public_configs = [ ":terminfo_config" ]
+  }
+}

llvm/utils/gn/build/libs/terminfo/enable.gni

+declare_args() {
+  # Whether to link against terminfo.
+  llvm_enable_terminfo = false
+}

llvm/utils/gn/build/libs/xml/BUILD.gn

+import("//llvm/utils/gn/build/libs/xml/enable.gni")
+import("//llvm/utils/gn/build/mac_sdk.gni")
+
+config("xml_config") {
+  visibility = [ ":xml" ]
+  defines = [ "LLVM_LIBXML2_ENABLED" ]
+  libs = [ "xml2" ]
+  if (host_os == "mac") {
+    include_dirs = [ "$mac_sdk/usr/include/libxml2" ]
+  } else {
+    include_dirs = [ "/usr/include/libxml2" ]
+  }
+}
+
+group("xml") {
+  if (llvm_enable_libxml2) {
+    public_configs = [ ":xml_config" ]
+  }
+}

llvm/utils/gn/build/libs/xml/enable.gni

+declare_args() {
+  # Whether to include code that links against libxml2.
+  llvm_enable_libxml2 = host_os != "win"
+}

llvm/utils/gn/build/libs/zlib/BUILD.gn

+import("//llvm/utils/gn/build/libs/zlib/enable.gni")
+
+config("zlib_config") {
+  visibility = [ ":zlib" ]
+  libs = [ "z" ]
+}
+
+group("zlib") {
+  if (llvm_enable_zlib) {
+    public_configs = [ ":zlib_config" ]
+  }
+}

llvm/utils/gn/build/libs/zlib/enable.gni

+declare_args() {
+  # Whether to include code that links against zlib.
+  llvm_enable_zlib = host_os != "win"
+}

llvm/utils/gn/build/toolchain/BUILD.gn

toolchain("unix") {
   }
 
   tool("alink") {
     if (host_os == "mac") {
       command = "libtool -static -no_warning_for_no_symbols {{arflags}} -o {{output}} {{inputs}}"
     } else {
       # Remove the output file first so that ar doesn't try to modify the
       # existing file.
-      command = "rm -f {{output}} && ar rcsDT {{arflags}} -o {{output}} {{inputs}}"
+      command =
+          "rm -f {{output}} && ar rcsDT {{arflags}} -o {{output}} {{inputs}}"
     }
     description = "AR {{output}}"
     outputs = [
       "{{output_dir}}/{{target_output_name}}.a",
     ]
     output_prefix = "lib"
     default_output_dir = "{{root_out_dir}}/lib"
   }

llvm/utils/gn/build/write_cmake_config.py

+"""Processes a foo.h.cmake file and writes foo.h.
+
+Takes a list of KEY=VALUE pairs (where VALUE can be empty).
+
+Handles these types of lines (note that FOO= sets the value of FOO to the empty
+string, which is falsy, but FOO=0 sets it to '0' which is truthy):
+
+1.) #cmakedefine01 FOO
+    Checks if key FOO is set to a truthy value, and depending on that prints
+    one of the following two lines:
+
+        #define FOO 1
+        #define FOO 0
+
+2.) #cmakedefine FOO
+    Checks if key FOO is set to a truthy in value, and depending on that prints
+    one of the following two lines:
+
+        #define FOO
+        /* #undef FOO */
+
+3.) #cmakedefine FOO asdf${BAR}jkl
+    Checks if key FOO is set to a truthy values, and if so replaces all
+    variable references in `asdf${BAR}jkl` with their value and prints that
+    (else it prints the same undef line as the previous form):
+
+        #define FOO asdfBAR_VALjkl
+        /* #undef FOO */
+
+4.) #define FOO asdf{BAR}jkl
+    Always gets its variable values filled in, independent of FOO's value being
+    set:
+
+        #define FOO asdfBAR_VALjkl
+
+Fails if any of the KEY=VALUE arguments aren't needed for processing the
+.h.cmake file, or if the .h.cmake file has unreplaces ${VAR} references after
+processing all values.
+"""
+
+import argparse
+import os
+import re
+import sys
+
+
+def main():
+    parser = argparse.ArgumentParser(
+                 epilog=__doc__,
+                 formatter_class=argparse.RawDescriptionHelpFormatter)
+    parser.add_argument('input', help='input file')
+    parser.add_argument('values', nargs='*', help='several KEY=VALUE pairs')
+    parser.add_argument('-o', '--output', required=True,
+                        help='output file')
+    args = parser.parse_args()
+
+    values = {}
+    for value in args.values:
+        key, val = value.split('=', 1)
+        values[key] = val
+    unused_values = set(values.keys())
+
+    # Matches e.g. '${CLANG_FOO}' and captures CLANG_FOO in group 1.
+    var_re = re.compile(r'\$\{([^}]*)\}')
+
+    in_lines = open(args.input).readlines()
+    out_lines = []
+    for in_line in in_lines:
+        def repl(m):
+            unused_values.discard(m.group(1))
+            return values[m.group(1)]
+        if in_line.startswith('#cmakedefine01 '):
+            _, var = in_line.split()
+            out_lines.append('#define %s %d\n' % (var, 1 if values[var] else 0))
+            unused_values.discard(var)
+        elif in_line.startswith('#cmakedefine '):
+            _, var = in_line.split(None, 1)
+            try:
+                var, val = var.split(None, 1)
+            except:
+                var, val = var.rstrip(), '\n'
+            if values[var]:
+                out_lines.append('#define %s %s' % (var,
+                                                    var_re.sub(repl, val)))
+            else:
+                out_lines.append('/* #undef %s */\n' % var)
+            unused_values.discard(var)
+        else:
+            # In particular, handles `#define FOO ${FOO}` lines.
+            out_lines.append(var_re.sub(repl, in_line))
+
+    if unused_values:
+        print >>sys.stderr, 'Unused --values args:'
+        print >>sys.stderr, '    ', '\n    '.join(unused_values)
+        return 1
+
+    output = ''.join(out_lines)
+
+    leftovers = var_re.findall(output)
+    if leftovers:
+        print >>sys.stderr, 'unprocessed values:\n', '\n'.join(leftovers)
+        return 1
+
+    if not os.path.exists(args.output) or open(args.output).read() != output:
+        open(args.output, 'w').write(output)
+
+
+if __name__ == '__main__':
+    sys.exit(main())

llvm/utils/gn/secondary/BUILD.gn

 group("default") {
   deps = [
-    "//llvm/lib/Demangle",
+    "//llvm/tools/llvm-undname",
   ]
 }
 
 # A pool called "console" in the root BUILD.gn is magic and represents ninja's
 # built-in console pool. (Requires a GN with `gn --version` >= 552353.)
 pool("console") {
   depth = 1
 }

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

+import("//llvm/utils/gn/build/buildflags.gni")
+import("//llvm/utils/gn/build/libs/pthread/enable.gni")
+import("//llvm/utils/gn/build/libs/terminfo/enable.gni")
+import("//llvm/utils/gn/build/libs/xml/enable.gni")
+import("//llvm/utils/gn/build/libs/zlib/enable.gni")
+import("//llvm/lib/Target/targets.gni")
+import("//llvm/triples.gni")
+import("//llvm/version.gni")
+
+# Contains actions to create config.h, llvm-config.h and abi-breaking.h.
+# Other than in the cmake build, these are created at build time, not at
+# config time. That way, they can run in parallel, and this pattern means that
+# e.g. creating the clang config header (which happens in another gn file)
+# doesn't block building lld.
+
+# The headers are created by processing the foo.h.cmake files as input,
+# to keep the gn build close to the cmake build.
+
+# Other than in the cmake build, header generation doesn't do any feature
+# checking. See also "Philosophy" in llvm/utils/gn/README.rst.
+
+# FIXME: Several of the config settings go in a global config header but
+# are only used in a single translation unit -- so toggling that value
+# causes a full rebuild when it really only has to rebuild a single file.
+# Instead monolithing config headers, investigate using something like
+# https://is.gd/buildflag_header_gni instead (needs to be done in both the
+# cmake build and here).
+
+# FIXME: This hardcodes a bunch of settings I never use; some of them should
+# become declare_args if anyone wants to set them.
+
+declare_args() {
+  # Enable additional checks that alter the LLVM C++ ABI.
+  llvm_enable_abi_breaking_checks = llvm_enable_assertions
+
+  # Iterate unordered llvm containers in reverse.
+  llvm_enable_reverse_iteration = false
+}
+
+action("abi-breaking") {
+  script = "//llvm/utils/gn/build/write_cmake_config.py"
+
+  sources = [
+    "abi-breaking.h.cmake",
+  ]
+  outputs = [
+    "$target_gen_dir/abi-breaking.h",
+  ]
+  args = [
+    "-o",
+    rebase_path(outputs[0], root_out_dir),
+
+    rebase_path(sources[0], root_out_dir),
+  ]
+
+  if (llvm_enable_abi_breaking_checks) {
+    args += [ "LLVM_ENABLE_ABI_BREAKING_CHECKS=1" ]
+  } else {
+    args += [ "LLVM_ENABLE_ABI_BREAKING_CHECKS=" ]
+  }
+
+  if (llvm_enable_reverse_iteration) {
+    args += [ "LLVM_ENABLE_REVERSE_ITERATION=1" ]
+  } else {
+    args += [ "LLVM_ENABLE_REVERSE_ITERATION=" ]
+  }
+}
+
+action("config") {
+  script = "//llvm/utils/gn/build/write_cmake_config.py"
+
+  public_deps = [
+    ":llvm-config",
+  ]
+
+  sources = [
+    "config.h.cmake",
+  ]
+  outputs = [
+    "$target_gen_dir/config.h",
+  ]
+  args = [
+    "-o",
+    rebase_path(outputs[0], root_out_dir),
+    rebase_path(sources[0], root_out_dir),
+
+    "BUG_REPORT_URL=https://bugs.llvm.org/",
+    "ENABLE_BACKTRACES=1",
+    "ENABLE_CRASH_OVERRIDES=1",
+    "BACKTRACE_HEADER=execinfo.h",
+    "HAVE_CRASHREPORTERCLIENT_H=",
+    "HAVE_DECL_FE_ALL_EXCEPT=1",
+    "HAVE_DECL_FE_INEXACT=1",
+    "LLVM_ENABLE_DIA_SDK=",
+    "LLVM_ENABLE_CRASH_DUMPS=",
+    "HAVE_ERRNO_H=1",
+    "HAVE_FCNTL_H=1",
+    "HAVE_FENV_H=1",
+    "HAVE_FFI_CALL=",
+    "HAVE_FFI_FFI_H=",
+    "HAVE_FFI_H=",
+    "HAVE_LIBPFM=",
+    "HAVE_LIBPSAPI=",
+    "HAVE_MALLCTL=",
+    "HAVE_SIGNAL_H=1",
+    "HAVE_STRERROR=1",
+    "HAVE_SYS_STAT_H=1",
+    "HAVE_SYS_TYPES_H=1",
+    "HAVE__ALLOCA=",
+    "HAVE___ALLOCA=",
+    "HAVE___ASHLDI3=",
+    "HAVE___ASHRDI3=",
+    "HAVE___CHKSTK=",
+    "HAVE___CHKSTK_MS=",
+    "HAVE___CMPDI2=",
+    "HAVE___DIVDI3=",
+    "HAVE___FIXDFDI=",
+    "HAVE___FIXSFDI=",
+    "HAVE___FLOATDIDF=",
+    "HAVE___LSHRDI3=",
+    "HAVE___MAIN=",
+    "HAVE___MODDI3=",
+    "HAVE___UDIVDI3=",
+    "HAVE___UMODDI3=",
+    "HAVE____CHKSTK=",
+    "HAVE____CHKSTK_MS=",
+    "HOST_LINK_VERSION=",
+    "LLVM_TARGET_TRIPLE_ENV=",
+    "LLVM_VERSION_INFO=",
+    "LLVM_VERSION_PRINTER_SHOW_HOST_TARGET_INFO=1",
+    "PACKAGE_BUGREPORT=https://bugs.llvm.org/",
+    "PACKAGE_NAME=LLVM",
+    "PACKAGE_STRING=LLVM ${llvm_version}svn",
+    "PACKAGE_VERSION=${llvm_version}svn",
+    "PACKAGE_VENDOR=",
+    "RETSIGTYPE=void",
+    "LLVM_GISEL_COV_ENABLED=",
+    "LLVM_GISEL_COV_PREFIX=",
+
+    # This is both in llvm-config.h and config.h; llvm-config.h doesn't
+    # define it if it's not set while config.h defines it to empty in that case.
+    "LLVM_DEFAULT_TARGET_TRIPLE=$llvm_target_triple",
+  ]
+
+  if (host_os == "linux") {
+    args += [
+      "HAVE_FUTIMENS=1",
+      "HAVE_LINK_H=1",
+      "HAVE_LSEEK64=1",
+      "HAVE_MALLINFO=1",
+      "HAVE_POSIX_FALLOCATE=1",
+      "HAVE_SCHED_GETAFFINITY=1",
+      "HAVE_CPU_COUNT=1",
+      "HAVE_VALGRIND_VALGRIND_H=1",
+    ]
+  } else {
+    args += [
+      "HAVE_FUTIMENS=",
+      "HAVE_LINK_H=",
+      "HAVE_LSEEK64=",
+      "HAVE_MALLINFO=",
+      "HAVE_POSIX_FALLOCATE=",
+      "HAVE_SCHED_GETAFFINITY=",
+      "HAVE_CPU_COUNT=",
+      "HAVE_VALGRIND_VALGRIND_H=",
+    ]
+  }
+
+  if (host_os == "mac") {
+    args += [
+      "HAVE_CRASHREPORTER_INFO=1",
+      "HAVE_DECL_ARC4RANDOM=1",
+      "HAVE_DLADDR=1",
+      "HAVE_LIBEDIT=1",
+      "HAVE_MALLOC_H=",
+      "HAVE_MACH_MACH_H=1",
+      "HAVE_MALLOC_MALLOC_H=1",
+      "HAVE_MALLOC_ZONE_STATISTICS=1",
+      "HAVE_LIBXAR=1",
+    ]
+  } else {
+    args += [
+      "HAVE_CRASHREPORTER_INFO=",
+      "HAVE_DECL_ARC4RANDOM=",
+      "HAVE_DLADDR=",
+      "HAVE_LIBEDIT=",
+      "HAVE_MACH_MACH_H=",
+      "HAVE_MALLOC_H=1",
+      "HAVE_MALLOC_MALLOC_H=",
+      "HAVE_MALLOC_ZONE_STATISTICS=",
+      "HAVE_LIBXAR=",
+    ]
+  }
+
+  if (host_os == "win") {
+    args += [
+      "HAVE_BACKTRACE=",
+      "HAVE_DECL_STRERROR_S=1",
+      "HAVE_DLFCN_H=",
+      "HAVE_DLOPEN=",
+      "HAVE_FUTIMES=",
+      "HAVE_GETPAGESIZE=",
+      "HAVE_GETRLIMIT=",
+      "HAVE_GETRUSAGE=",
+      "HAVE_ISATTY=",
+      "HAVE_LIBPTHREAD=",
+      "HAVE_PTHREAD_GETNAME_NP=",
+      "HAVE_PTHREAD_SETNAME_NP=",
+      "HAVE_LIBZ=",
+      "HAVE_POSIX_SPAWN=",
+      "HAVE_PREAD=",
+      "HAVE_PTHREAD_GETSPECIFIC=",
+      "HAVE_PTHREAD_H=",
+      "HAVE_PTHREAD_MUTEX_LOCK=",
+      "HAVE_PTHREAD_RWLOCK_INIT=",
+      "HAVE_REALPATH=",
+      "HAVE_SBRK=",
+      "HAVE_SETENV=",
+      "HAVE_SETRLIMIT=",
+      "HAVE_SIGALTSTACK=",
+      "HAVE_STRERROR_R=",
+      "HAVE_SYSCONF=",
+      "HAVE_SYS_IOCTL_H=",
+      "HAVE_SYS_MMAN_H=",
+      "HAVE_SYS_PARAM_H=",
+      "HAVE_SYS_RESOURCE_H=",
+      "HAVE_SYS_TIME_H=",
+      "HAVE_TERMIOS_H=",
+      "HAVE_UNISTD_H=",
+      "HAVE_ZLIB_H=",
+      "HAVE__CHSIZE_S=1",
+      "HAVE__UNWIND_BACKTRACE=",
+      "stricmp=_stricmp",
+      "strdup=_strdup",
+    ]
+  } else {
+    # POSIX-y system defaults.
+    args += [
+      "HAVE_BACKTRACE=1",
+      "HAVE_DECL_STRERROR_S=",
+      "HAVE_DLFCN_H=1",
+      "HAVE_DLOPEN=1",
+      "HAVE_FUTIMES=1",
+      "HAVE_GETPAGESIZE=1",
+      "HAVE_GETRLIMIT=1",
+      "HAVE_GETRUSAGE=1",
+      "HAVE_ISATTY=1",
+      "HAVE_LIBPTHREAD=1",
+      "HAVE_PTHREAD_GETNAME_NP=1",
+      "HAVE_PTHREAD_SETNAME_NP=1",
+      "HAVE_LIBZ=1",
+      "HAVE_POSIX_SPAWN=1",
+      "HAVE_PREAD=1",
+      "HAVE_PTHREAD_GETSPECIFIC=1",
+      "HAVE_PTHREAD_H=1",
+      "HAVE_PTHREAD_MUTEX_LOCK=1",
+      "HAVE_PTHREAD_RWLOCK_INIT=1",
+      "HAVE_REALPATH=1",
+      "HAVE_SBRK=1",
+      "HAVE_SETENV=1",
+      "HAVE_SETRLIMIT=1",
+      "HAVE_SIGALTSTACK=1",
+      "HAVE_STRERROR_R=1",
+      "HAVE_SYSCONF=1",
+      "HAVE_SYS_IOCTL_H=1",
+      "HAVE_SYS_MMAN_H=1",
+      "HAVE_SYS_PARAM_H=1",
+      "HAVE_SYS_RESOURCE_H=1",
+      "HAVE_SYS_TIME_H=1",
+      "HAVE_TERMIOS_H=1",
+      "HAVE_UNISTD_H=1",
+      "HAVE_ZLIB_H=1",
+      "HAVE__CHSIZE_S=",
+      "HAVE__UNWIND_BACKTRACE=1",
+      "stricmp=",
+      "strdup=",
+    ]
+  }
+
+  if (host_os == "linux") {
+    args += [ "LTDL_SHLIB_EXT=.so" ]
+  } else if (host_os == "mac") {
+    args += [ "LTDL_SHLIB_EXT=.dylib" ]
+  } else if (host_os == "win") {
+    args += [ "LTDL_SHLIB_EXT=.dll" ]
+  }
+
+  if (llvm_enable_terminfo) {
+    args += [ "HAVE_TERMINFO=1" ]
+  } else {
+    args += [ "HAVE_TERMINFO=" ]
+  }
+
+  if (llvm_enable_zlib) {
+    args += [ "LLVM_ENABLE_ZLIB=1" ]
+  } else {
+    args += [ "LLVM_ENABLE_ZLIB=" ]
+  }
+
+  if (llvm_enable_libxml2) {
+    args += [ "LLVM_LIBXML2_ENABLED=1" ]
+  } else {
+    args += [ "LLVM_LIBXML2_ENABLED=" ]
+  }
+}
+
+action("llvm-config") {
+  script = "//llvm/utils/gn/build/write_cmake_config.py"
+
+  sources = [
+    "llvm-config.h.cmake",
+  ]
+  outputs = [
+    "$target_gen_dir/llvm-config.h",
+  ]
+  args = [
+    "-o",
+    rebase_path(outputs[0], root_out_dir),
+    rebase_path(sources[0], root_out_dir),
+
+    "LLVM_ENABLE_DUMP=",
+    "LINK_POLLY_INTO_TOOLS=",
+    "LLVM_DEFAULT_TARGET_TRIPLE=$llvm_target_triple",
+    "LLVM_HAS_ATOMICS=1",
+    "LLVM_HOST_TRIPLE=$llvm_host_triple",
+    "LLVM_NATIVE_ARCH=$native_target",
+    "LLVM_NATIVE_ASMPARSER=1",
+    "LLVM_NATIVE_ASMPRINTER=1",
+    "LLVM_NATIVE_DISASSEMBLER=1",
+    "LLVM_NATIVE_TARGET=1",
+    "LLVM_NATIVE_TARGETINFO=1",
+    "LLVM_NATIVE_TARGETMC=1",
+    "LLVM_USE_INTEL_JITEVENTS=",
+    "LLVM_USE_OPROFILE=",
+    "LLVM_USE_PERF=",
+    "LLVM_VERSION_MAJOR=$llvm_version_major",
+    "LLVM_VERSION_MINOR=$llvm_version_minor",
+    "LLVM_VERSION_PATCH=$llvm_version_patch",
+    "PACKAGE_VERSION=${llvm_version}svn",
+    "LLVM_FORCE_ENABLE_STATS=",
+  ]
+
+  if (host_os == "win") {
+    args += [ "LLVM_ON_UNIX=" ]
+  } else {
+    args += [ "LLVM_ON_UNIX=1" ]
+  }
+
+  if (llvm_enable_threads) {
+    args += [ "LLVM_ENABLE_THREADS=1" ]
+  } else {
+    args += [ "LLVM_ENABLE_THREADS=" ]
+  }
+}

llvm/utils/gn/secondary/llvm/lib/Support/BUILD.gn

+static_library("Support") {
+  output_name = "LLVMSupport"
+  deps = [
+    "//llvm/include/llvm/Config:config",
+    "//llvm/lib/Demangle",
+    "//llvm/utils/gn/build/libs/pthread",
+    "//llvm/utils/gn/build/libs/terminfo",
+    "//llvm/utils/gn/build/libs/zlib",
+  ]
+
+  # public_deps are used for depending on targets that generate headers
+  # which are included in public headers of this target. public_deps means
+  # that targets depending on Support will implicitly be built only after
+  # abi-breaking and llvm-config have been built.
+  public_deps = [
+    # abi-breaking.h is also include by public headers in ADT, but ADT has
+    # no target in the gn build.  Since everything depends on Support, this
+    # public_dep does double duty of abi-breaking.h uses in public headers of
+    # both Support and ADT.
+    "//llvm/include/llvm/Config:abi-breaking",
+    "//llvm/include/llvm/Config:llvm-config",
+  ]
+  include_dirs = [
+    "Unix",
+    "Windows",
+  ]
+  sources = [
+    "AMDGPUMetadata.cpp",
+    "APFloat.cpp",
+    "APInt.cpp",
+    "APSInt.cpp",
+    "ARMAttributeParser.cpp",
+    "ARMBuildAttrs.cpp",
+    "ARMWinEH.cpp",
+    "Allocator.cpp",
+    "BinaryStreamError.cpp",
+    "BinaryStreamReader.cpp",
+    "BinaryStreamRef.cpp",
+    "BinaryStreamWriter.cpp",
+    "BlockFrequency.cpp",
+    "BranchProbability.cpp",
+    "COM.cpp",
+    "CachePruning.cpp",
+    "Chrono.cpp",
+    "CodeGenCoverage.cpp",
+    "CommandLine.cpp",
+    "Compression.cpp",
+    "ConvertUTF.cpp",
+    "ConvertUTFWrapper.cpp",
+    "CrashRecoveryContext.cpp",
+    "DAGDeltaAlgorithm.cpp",
+    "DJB.cpp",
+    "DataExtractor.cpp",
+    "Debug.cpp",
+    "DebugCounter.cpp",
+    "DeltaAlgorithm.cpp",
+    "Error.cpp",
+    "ErrorHandling.cpp",
+    "FileCheck.cpp",
+    "FileOutputBuffer.cpp",
+    "FileUtilities.cpp",
+    "FoldingSet.cpp",
+    "FormatVariadic.cpp",
+    "FormattedStream.cpp",
+    "GlobPattern.cpp",
+    "GraphWriter.cpp",
+    "Hashing.cpp",
+    "InitLLVM.cpp",
+    "IntEqClasses.cpp",
+    "IntervalMap.cpp",
+    "ItaniumManglingCanonicalizer.cpp",
+    "JSON.cpp",
+    "JamCRC.cpp",
+    "KnownBits.cpp",
+    "LEB128.cpp",
+    "LineIterator.cpp",
+    "Locale.cpp",
+    "LockFileManager.cpp",
+    "LowLevelType.cpp",
+    "MD5.cpp",
+    "ManagedStatic.cpp",
+    "MathExtras.cpp",
+    "MemoryBuffer.cpp",
+    "NativeFormatting.cpp",
+    "Options.cpp",
+    "Parallel.cpp",
+    "PluginLoader.cpp",
+    "PrettyStackTrace.cpp",
+    "RandomNumberGenerator.cpp",
+    "Regex.cpp",
+    "SHA1.cpp",
+    "ScaledNumber.cpp",
+    "ScopedPrinter.cpp",
+    "SmallPtrSet.cpp",
+    "SmallVector.cpp",
+    "SourceMgr.cpp",
+    "SpecialCaseList.cpp",
+    "Statistic.cpp",
+    "StringExtras.cpp",
+    "StringMap.cpp",
+    "StringPool.cpp",
+    "StringRef.cpp",
+    "StringSaver.cpp",
+    "SymbolRemappingReader.cpp",
+    "SystemUtils.cpp",
+    "TarWriter.cpp",
+    "TargetParser.cpp",
+    "ThreadPool.cpp",
+    "Timer.cpp",
+    "ToolOutputFile.cpp",
+    "TrigramIndex.cpp",
+    "Triple.cpp",
+    "Twine.cpp",
+    "Unicode.cpp",
+    "UnicodeCaseFold.cpp",
+    "VersionTuple.cpp",
+    "WithColor.cpp",
+    "YAMLParser.cpp",
+    "YAMLTraits.cpp",
+    "circular_raw_ostream.cpp",
+    "raw_os_ostream.cpp",
+    "raw_ostream.cpp",
+    "regcomp.c",
+    "regerror.c",
+    "regexec.c",
+    "regfree.c",
+    "regstrlcpy.c",
+    "xxhash.cpp",
+
+    # System
+    "Atomic.cpp",
+    "DynamicLibrary.cpp",
+    "Errno.cpp",
+    "Host.cpp",
+    "Memory.cpp",
+    "Mutex.cpp",
+    "Path.cpp",
+    "Process.cpp",
+    "Program.cpp",
+    "RWMutex.cpp",
+    "Signals.cpp",
+    "TargetRegistry.cpp",
+    "ThreadLocal.cpp",
+    "Threading.cpp",
+    "Valgrind.cpp",
+    "VirtualFileSystem.cpp",
+    "Watchdog.cpp",
+  ]
+
+  libs = []
+
+  if (host_os == "linux") {
+    libs += [ "dl" ]
+  }
+}

llvm/utils/gn/secondary/llvm/lib/Target/targets.gni

+declare_args() {
+  # The target archs LLVM should support. Defaults to the host arch.
+  # Set to a list, e.g. `llvm_targets_to_build = [ "X86", "ARM" ]`,
+  # or to the string "all" to get all known targets.
+  llvm_targets_to_build = "host"
+}
+
+if (llvm_targets_to_build == "host") {
+  if (host_cpu == "x86" || host_cpu == "x64") {
+    llvm_targets_to_build = [ "X86" ]
+  } else if (host_cpu == "arm") {
+    llvm_targets_to_build = [ "ARM" ]
+  } else if (host_cpu == "arm64") {
+    llvm_targets_to_build = [ "AArch64" ]
+  } else {
+    assert(false, "add your host_cpu above")
+  }
+} else if (llvm_targets_to_build == "all") {
+  # FIXME: Port the remaining targets.
+  llvm_targets_to_build = [
+    "AArch64",
+    "ARM",
+    "X86",
+  ]
+}
+
+# Validate that llvm_targets_to_build is set to a list of valid targets,
+# and remember which targets are built.
+llvm_build_AArch64 = false
+llvm_build_ARM = false
+llvm_build_X86 = false
+foreach(target, llvm_targets_to_build) {
+  # FIXME: Port the remaining targets.
+  assert(target == "AArch64" || target == "ARM" || target == "X86",
+         "Unknown target '$target'.")
+  if (target == "AArch64") {
+    llvm_build_AArch64 = true
+  } else if (target == "ARM") {
+    llvm_build_ARM = true
+  } else if (target == "X86") {
+    llvm_build_X86 = true
+  }
+}
+
+# FIXME: This should be based off target_cpu once cross compiles work.
+if (host_cpu == "x86" || host_cpu == "x64") {
+  native_target = "X86"
+} else if (host_cpu == "arm") {
+  native_target = "ARM"
+} else if (host_cpu == "arm64") {
+  native_target = "AArch64"
+} else {
+  assert(false)
+}

llvm/utils/gn/secondary/llvm/tools/llvm-undname/BUILD.gn

+executable("llvm-undname") {
+  deps = [
+    "//llvm/lib/Demangle",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "llvm-undname.cpp",
+  ]
+}

llvm/utils/gn/secondary/llvm/triples.gni

+if (host_os == "linux") {
+  llvm_host_triple = "x86_64-unknown-linux-gnu"
+} else if (host_os == "mac") {
+  llvm_host_triple = "x86_64-apple-darwin"
+} else if (host_os == "win") {
+  llvm_host_triple = "x86_64-pc-windows"
+}
+
+declare_args() {
+  # The default target triple.
+  llvm_target_triple = llvm_host_triple
+}

llvm/utils/gn/secondary/llvm/version.gni

+llvm_version_major = 8
+llvm_version_minor = 0
+llvm_version_patch = 0
+llvm_version = "$llvm_version_major.$llvm_version_minor.$llvm_version_patch"