serenity/Meta/gn/build/BUILD.gn

import("//Meta/gn/build/buildflags.gni")
import("//Meta/gn/build/mac_sdk.gni")
import("//Meta/gn/build/sysroot.gni")
import("//Meta/gn/build/toolchain/compiler.gni")

declare_args() {
  # If set, puts relative paths in debug info.
  # Makes the build output independent of the build directory, but makes
  # most debuggers harder to use. See "Getting to local determinism" and
  # "Getting debuggers to work well with locally deterministic builds" in
  # http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
  # for more information.
  use_relative_paths_in_debug_info = false

  # The version of host gcc. Ignored if is_clang is true.
  gcc_version = 12
}

config("compiler_defaults") {
  defines = []
  asmflags = []
  cflags = []
  cflags_cc = []
  ldflags = []

  if (symbol_level == 2) {
    if (is_debug_gdb) {
      cflags += [ "-ggdb" ]
    } else if (is_clang && is_debug_lldb) {
      # GCC (as of version 13) does not support lldb-specific debug information
      cflags += [ "-glldb" ]
    } else {
      cflags += [ "-g" ]
    }

    # For full debug-info -g builds, --gdb-index makes links ~15% slower, and
    # gdb symbol reading time 1500% faster (lld links in 4.4 instead of 3.9s,
    # and gdb loads and runs it in 2s instead of in 30s).  It's likely that
    # people doing symbol_level=2 want to run a debugger (since
    # symbol_level=2 isn't the default). So this seems like the right
    # tradeoff.
    if (current_os != "mac" && use_lld) {
      cflags += [ "-ggnu-pubnames" ]  #  llvm PR34820
      ldflags += [ "-Wl,--gdb-index" ]

      # Use debug fission. In this mode, detailed debug information is
      # written to a .dwo file next to each .o file instead of into the .o
      # file directly. The linker then only links the .o files, which contain
      # a pointer to each .dwo file. The debugger then reads debug info out
      # of all the .dwo files instead of from the binary.
      #
      # (The dwp tool can link all the debug info together into a single
      # "debug info binary", but that's not done as part of the build.)
      #
      # This requires `-Wl,--gdb-index` (above) to work well.
      #
      # With lld, this reduces link time:
      # - in release + symbol_level=2 builds: From 2.3s to 1.3s
      # - in debug builds: From 5.2s to 4.6s
      #
      # Time needed for gdb startup and setting a breakpoint is comparable,
      # the time from from `r` to hititng a breakpoint on main goes from 4s
      # to 2s.
      #
      # (macOS's linker always keeps debug info out of its output executables
      # and debuggers there also know to load debug info from the .o files.
      # macOS also has a debug info linker like dwp, it's called dsymutil.
      # This happens by default, so there's no need to pass a flag there.)
      cflags += [ "-gsplit-dwarf" ]
      ldflags += [ "-gsplit-dwarf" ]  # Needed for ThinLTO builds.
    }
  } else if (symbol_level == 1) {
    cflags += [ "-g1" ]
    # For linetable-only -g1 builds, --gdb-index makes links ~8% slower, but
    # links are 4x faster than -g builds so it's a fairly small absolute cost.
    # On the other hand, gdb startup is well below 1s with and without the
    # index, and people using -g1 likely don't use a debugger. So don't use
    # the flag here.
    # Linetables always go in the .o file, even with -gsplit-dwarf, so there's
    # no point in passing -gsplit-dwarf here.
  }
  if (is_optimized) {
    cflags += [ "-O3" ]
  }
  cflags += [ "-fdiagnostics-color" ]

  cflags += [ "-ffp-contract=off" ]

  if (use_lld) {
    ldflags += [ "-Wl,--color-diagnostics" ]
  }
  cflags_cc += [
    "-std=c++20",
    "-fvisibility-inlines-hidden",
  ]

  # Warning setup.
  cflags += [
    "-Wall",
    "-Wextra",
  ]
  cflags += [
    "-Wno-unused-parameter",
    "-Wno-invalid-offsetof",
  ]
  if (is_clang) {
    cflags += [
      "-Wdelete-non-virtual-dtor",
      "-Wstring-conversion",
      "-Wno-user-defined-literals",
      "-fconstexpr-steps=16777216",
      "-Wno-unused-private-field",
      "-Wno-implicit-const-int-float-conversion",
    ]
  } else {
    cflags += [
      # Disable gcc's potentially uninitialized use analysis as it presents
      # lots of false positives.
      "-Wno-maybe-uninitialized",

      # Disable -Wredundant-move on GCC>=9. GCC wants to remove std::move
      # in code like "A foo(ConvertibleToA a) { return std::move(a); }",
      # but this code does not compile (or uses the copy constructor
      # instead) on clang<=3.8. Clang also has a -Wredundant-move, but it
      # only fires when the types match exactly, so we can keep it here.
      "-Wno-redundant-move",

      "-Wno-literal-suffix",
    ]
  }

  if (use_lld) {
    ldflags += [ "-fuse-ld=lld" ]
  }

  # Deterministic build setup, see
  # http://blog.llvm.org/2019/11/deterministic-builds-with-clang-and-lld.html
  if (is_clang) {
    cflags += [
      "-no-canonical-prefixes",
      "-Werror=date-time",
    ]
    if (use_relative_paths_in_debug_info) {
      cflags += [ "-fdebug-compilation-dir=." ]
    }
  }
  if (sysroot != "") {
    if (current_os != "mac" && current_os != "android") {
      cflags += [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
      ldflags += [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
    }
  }

  if (current_os == "mac") {
    sdk_path = mac_sdk_path
    cflags += [
      "-isysroot",
      rebase_path(sdk_path, root_build_dir),
    ]
    ldflags += [
      "-isysroot",
      rebase_path(sdk_path, root_build_dir),
    ]
  }
  if (sysroot != "" && current_os != "win" && is_clang) {
    cflags += [ "-Wpoison-system-directories" ]
  }
  cflags_objcc = cflags_cc
}

config("no_exceptions") {
  cflags_cc = [ "-fno-exceptions" ]
  cflags_objcc = cflags_cc
}

config("zdefs") {
  if (current_os != "mac" && current_os != "android") {
    ldflags = [ "-Wl,-z,defs" ]
  }
}

config("pic") {
  if (current_os != "mac") {
    cflags_cc = [ "-fPIC" ]
  }
}