* USE_CLANG_LLD is unedefined in current builds.
* When USE_CLANG_LLD is defined to 'true' or '1',
use clang's lld instead of ld or ld.gold.
* When lld is enabled:
* ld-only flags are not passed to 'lld'.
* location_packer is disabled.
* Use new lld's --pack-dyn-relocs=android.
* When lld does not work:
* In Android.mk files use LOCAL_USE_CLANG_LLD := false.
* In Android.bp files use use_clang_lld: false.
* Only arm, arm64, x86, and x86_64_devices have LLD flags;
all other hosts and targets do not call lld yet.
Bug: 73768157
Test: make checkbuild and boot
Change-Id: I06b8a1e868a600997a7e70fe05c299d751d23d5f
* Suppress more noisy new warnings at global level.
* Add -no-pie to partial link .o files, with -r.
* Revert workaround of b/72706604, no need of
-Wl,-plugin-opt,-emulated-tls
* Filter out clang 7.0 unknown flag "-Wno-extended-offsetof"
Bug: 72706604
Bug: 72412006
Test: make checkbuild
Change-Id: I7ff45465c4bd771991f42b40f68dc35586045656
Allow developers to enable ThinLTO caching on their local build by
setting USE_THINLTO_CACHE environment variable.
This significantly speeds up incremental ThinLTO builds by caching
intermediate results. An incremental ART build (by `touch
compiler/compiler.cc`) reduced from 01:32 to 00:45.
We put the cache under out/soong/thinlto-cache as the cache can be
valid across different targets, and allows us to set a global cache
pruning policy.
The current cache policy is sufficient for current list of
ThinLTO-enabled projects, we can tune it up/down in the future.
Test: USE_THINLTO_CACHE=true m
Bug: 62839002
Change-Id: I4838fe833a1d8fbc73d743da6d19e3698dc89600
Such optimisations may significantly increase the binary size when
compiler heuristics are off. Disabling these helps cut down the
binary sizes with negligible decrease in performance, but allows us to
be more comfortable enabling LTO across various projects.
Test: m
Test: dex2oat, hwui, skia benchmark
Bug: 62839002
Change-Id: Id63e8dd295df2972f76ae4e29ee367080fff8429
LLVM-AR does not allow passing --plugin options more than once. The
--plugin ARFLAGS that lto want to add, may already exist if sanitizer is
also turned on.
Fixed this by adding a new bool Flags.ArGoldPlugin. Set this variable to
true whenever LLVM gold plugin is needed for ArFlags. In function
TransformObjToStaticLib(), add this option to arFlags using global value
${config.LLVMGoldPlugin} if the bool value is true.
Bug: http://b/73160350
Test: build the image with make and succeeded.
Change-Id: I62785829b0a4b663225926e4aed98defc1b6da2c
(cherry picked from commit 4917049f6e)
-fsanitize=cfi requires LTO. Normally, the Clang driver automatically
enables emutls, but it's broken with -flto, so work around it by passing
-Wl,-plugin-opt=-emulated-tls.
See https://buganizer.corp.google.com/issues/72706604#comment15
Enable the workaround with ctx.Device(), which is the same condition used
in the existing I18acac41aac885fc6635fbd55f96ba7c845eb5e7 workaround.
Bug: b/72706604
Bug: https://github.com/android-ndk/ndk/issues/498
Test: m libaudioflinger (on internal master); \
readelf -sW symbols/system/lib64/libaudioflinger.so | grep tlNBLogWriter
check that __emutls_t.tlNBLogWriter exists
check that no symbols of type TLS exist
Change-Id: I2cf65574c52476843cc017ee176a7d6777e2ce0b
Allow developers to disable LTO to reduce build time.
Test: m checkbuild
Test: DISABLE_LTO=true m checkbuild
Bug: 62839002
Change-Id: I30642e3cfff60c4874a2f8797d08105b4e07cc6d
Propagation of LTO flags from a main binary or library to its static
dependencies is necessary so that objects being linked with LTO are built as
bitcode rather than native objects. This propagation was broken when thin LTO
was added to the build system. This patch propagates the LTO mode (thin or full)
down to object and archive dependencies.
Test: Build libhwui with full and thin LTO and check that intermediate objects
are LLVM bitcode.
Change-Id: Ic57a80d75052d86940db076fbc0f5375a79c89a1
Also adds checks that the dependencies are android.Modules and
are not disabled.
Test: m checkbuild
Change-Id: I05e945f38915d49cd3c0ab72a86576949bc7eff2
ThinLTO achieves comparable performance to full LTO while taking much
less time for compilation.
Test: Build hwui with "thin" and "full" LTO
Change-Id: If3400b82af0d5e0226410c8b740999cdad746a59
In LTO mode the backend constructs a target exclusively from command line flags,
without opportunity to accept code gen arguments from Clang. Clang does not
currently pass the -emulated-tls parameter for Android, even though it defaults
to emulated TLS for Android in non-LTO builds. Until this is fixed upstream, we
can explicitly specify that the LTO output for Android should use emulated TLS.
Test: build libandroid with LTO, verified that it uses __emutls_get_address
rather than __tls_get_addr.
Change-Id: I18acac41aac885fc6635fbd55f96ba7c845eb5e7
Enabling the lto property for a module builds that module and all static
dependencies with LTO.
LTO (link-time optimization) allows the compiler to optimize and
generate code for the entire module at link time, rather than
per-compilation unit. LTO is required for Clang CFI and other
whole-program optimization techniques. LTO also allows cross-compilation
unit optimizations that should result in faster and smaller code, at the
expense of additional compilation time.
Test: make -j12 libc with lto: true for libc
Change-Id: Ib8baefedf60e02701d44673a7c473e0845730101
Chih-Hung Hsieh