meson's builtin LTO support allows meson to introspect whether LTO is
enabled and do some fancy things, such as forcing LTO off for a single
target that is known to be special(ly bad) and not support LTO.
Signed-off-by: Eli Schwartz <eschwart...@gmail.com>
---
eclass/meson.eclass | 36 ++++++++++++++++++++++++++++++++----
1 file changed, 32 insertions(+), 4 deletions(-)
diff --git a/eclass/meson.eclass b/eclass/meson.eclass
index d8bd93082ea5..c2ae289019e9 100644
--- a/eclass/meson.eclass
+++ b/eclass/meson.eclass
@@ -41,7 +41,7 @@ esac
if [[ -z ${_MESON_ECLASS} ]]; then
_MESON_ECLASS=1
-inherit multiprocessing ninja-utils python-utils-r1 toolchain-funcs
+inherit flag-o-matic multiprocessing ninja-utils python-utils-r1
toolchain-funcs
BDEPEND=">=dev-build/meson-1.2.1
${NINJA_DEPEND}
@@ -286,6 +286,36 @@ meson_src_configure() {
[[ -n "${NINJA_DEPEND}" ]] || ewarn "Unknown value '${NINJA}' for
\${NINJA}"
+ local ltoflags=()
+ if tc-is-lto; then
+ # We want to connect -flto in *FLAGS to the dedicated meson
option,
+ # to ensure that meson has visibility into what the user set.
Although
+ # it is unlikely projects will check `get_option('b_lto')` and
change
+ # their behavior, individual targets which are broken with LTO
can
+ # disable it per target. Injecting via *FLAGS means that meson
cannot
+ # strip -flto from that target.
+ ltoflags+=( -Db_lto=true )
+
+ # respect -flto value, e.g. -flto=8, -flto=thin
+ local v=$(get-flag flto)
+ case ${v} in
+ thin)
+ ltoflags+=( -Db_lto_mode=thin )
+ ;;
+ ''|*[!0-9]*)
+ ;;
+ *) ltoflags+=( -Db_lto_threads=${v} )
+ esac
+ # finally, remove it from *FLAGS to avoid passing it:
+ # - twice, with potentially different values
+ # - on excluded targets
+ filter-lto
+ else
+ # Prevent projects from enabling LTO by default. In Gentoo,
LTO is
+ # enabled via setting *FLAGS appropriately.
+ ltoflags+=( -Db_lto=false )
+ fi
+
local BUILD_CFLAGS=${BUILD_CFLAGS}
local BUILD_CPPFLAGS=${BUILD_CPPFLAGS}
local BUILD_CXXFLAGS=${BUILD_CXXFLAGS}
@@ -335,9 +365,7 @@ meson_src_configure() {
# an upstream development matter. bug #754279.
-Dwerror=false
- # Prevent projects from enabling LTO by default. In Gentoo,
LTO is
- # enabled via setting *FLAGS appropriately.
- -Db_lto=false
+ "${ltoflags[@]}"
)
if [[ -n ${EMESON_BUILDTYPE} ]]; then
--
2.43.0
