tree 91143a5c0fce4ac58135d009f3503ad9289be3e7
parent 160387be0d7d793757f5e7508a0cb0080fa7d70a
author Nico Weber <thakis@chromium.org> 1573150477 -0500
committer Commit Bot <commit-bot@chromium.org> 1573156269 +0000

win: Only use ICF and LTO if explicitly opted in.

The bots pass --use-icf and --use-lto, so it doesn't affect them.
Makes the Windows build more like the non-Windows build, and
makes incremental build times (== local dev) in the default build
config 20x faster.

(It also makes it possible to set CC/CXX to clang-cl without
getting warnings about /GL, but that's not my motivation here.
But I might want to use goma to build gn in the future, at least
on my laptop, and then that'll come in handy.)

Also add /Zc:inline to cflags in release builds on Windows.

Also change non-Win to use LTO only in release builds -- LTO in
debug builds doesn't make much sense.

Release build times (always `ninja -C out`, i.e. linking both
gn.exe and gn_unittests.exe):

With this patch:
Full: 4m25s
Touch just src\gn\command_analyze.cc: 3.8s
Size of out\: 844 MB
Peak memory use during build: 250 MB

With this patch but no /Zc:inline:
Full: 4m25s
Touch just src\gn\command_analyze.cc: 4.8s
Size of out\: 1.05 GB
Peak memory use during build: 345 MB

Without this patch (== this patch with --use-icf --use-lto;
/Zc:inline seems to have no effect when used with /GL):
Full: 4m33s
Touch just src\gn\command_analyze.cc: 1m55s (!)
Size of out\: 1.52 GB
Peak memory use during build: 678 MB

Change-Id: Idd87389c7537828fe6523a64de6031f9cbbc0fc6
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/6442
Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>