[all-commits] [llvm/llvm-project] 1217b4: [gn build] Build with Fission on non-mac non-win w...

Nico Weber via All-commits all-commits at lists.llvm.org
Fri Dec 3 08:08:16 PST 2021

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1217b4b46fce698cfbc869ec0f43b074f3f5f874
  Author: Nico Weber <thakis at chromium.org>
  Date:   2021-12-03 (Fri, 03 Dec 2021)

  Changed paths:
    M llvm/utils/gn/build/BUILD.gn

  Log Message:
  [gn build] Build with Fission on non-mac non-win when using lld

In release+sym builds (-O2 -g), reduces time to link `clang`
from 2.3s to 1.3s (-42%).

In debug builds (-g), reduces time to link `clang`
from 5.4s to 4.5s (-17.4%).

See the phab review for full `ministat` numbers.

In the CMake build this is opt-in via LLVM_USE_SPLIT_DWARF.
Since the GN build is targeted at developers, enabling it by default
seems like a better default setting here. (If it turns out to cause
problems, we can add an opt-out.)

Time to load the binary into gdb and to set a breakpoint is unchanged.
Time from `run` to hitting a breakpoint in `main` feel a bit faster
(~4s -> ~2s), but I dind't do a careful statistical anlysis for this.

Differential Revision: https://reviews.llvm.org/D115040

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