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// Copyright 2017 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package cc
import (
"github.com/google/blueprint/proptools"
"android/soong/android"
)
// 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.
//
// To properly build a module with LTO, the module and all recursive static
// dependencies should be compiled with -flto which directs the compiler to emit
// bitcode rather than native object files. These bitcode files are then passed
// by the linker to the LLVM plugin for compilation at link time. Static
// dependencies not built as bitcode will still function correctly but cannot be
// optimized at link time and may not be compatible with features that require
// LTO, such as CFI.
//
// This file adds support to soong to automatically propogate LTO options to a
// new variant of all static dependencies for each module with LTO enabled.
type LTOProperties struct {
// Lto must violate capitialization style for acronyms so that it can be
// referred to in blueprint files as "lto"
Lto struct {
Never *bool `android:"arch_variant"`
Full *bool `android:"arch_variant"`
Thin *bool `android:"arch_variant"`
} `android:"arch_variant"`
// Dep properties indicate that this module needs to be built with LTO
// since it is an object dependency of an LTO module.
FullDep bool `blueprint:"mutated"`
ThinDep bool `blueprint:"mutated"`
NoLtoDep bool `blueprint:"mutated"`
// Use clang lld instead of gnu ld.
Use_clang_lld *bool
// Use -fwhole-program-vtables cflag.
Whole_program_vtables *bool
}
type lto struct {
Properties LTOProperties
}
func (lto *lto) props() []interface{} {
return []interface{}{&lto.Properties}
}
func (lto *lto) begin(ctx BaseModuleContext) {
if ctx.Config().IsEnvTrue("DISABLE_LTO") {
lto.Properties.Lto.Never = proptools.BoolPtr(true)
}
}
func (lto *lto) useClangLld(ctx BaseModuleContext) bool {
if lto.Properties.Use_clang_lld != nil {
return Bool(lto.Properties.Use_clang_lld)
}
return true
}
func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
// TODO(b/131771163): Disable LTO when using explicit fuzzing configurations.
// LTO breaks fuzzer builds.
if inList("-fsanitize=fuzzer-no-link", flags.Local.CFlags) {
return flags
}
if lto.LTO(ctx) {
var ltoCFlag string
var ltoLdFlag string
if lto.ThinLTO() {
ltoCFlag = "-flto=thin -fsplit-lto-unit"
} else if lto.FullLTO() {
ltoCFlag = "-flto"
} else {
ltoCFlag = "-flto=thin -fsplit-lto-unit"
ltoLdFlag = "-Wl,--lto-O0"
}
flags.Local.CFlags = append(flags.Local.CFlags, ltoCFlag)
flags.Local.LdFlags = append(flags.Local.LdFlags, ltoCFlag)
flags.Local.LdFlags = append(flags.Local.LdFlags, ltoLdFlag)
if Bool(lto.Properties.Whole_program_vtables) {
flags.Local.CFlags = append(flags.Local.CFlags, "-fwhole-program-vtables")
}
if (lto.DefaultThinLTO(ctx) || lto.ThinLTO()) && ctx.Config().IsEnvTrue("USE_THINLTO_CACHE") && lto.useClangLld(ctx) {
// Set appropriate ThinLTO cache policy
cacheDirFormat := "-Wl,--thinlto-cache-dir="
cacheDir := android.PathForOutput(ctx, "thinlto-cache").String()
flags.Local.LdFlags = append(flags.Local.LdFlags, cacheDirFormat+cacheDir)
// Limit the size of the ThinLTO cache to the lesser of 10% of available
// disk space and 10GB.
cachePolicyFormat := "-Wl,--thinlto-cache-policy="
policy := "cache_size=10%:cache_size_bytes=10g"
flags.Local.LdFlags = append(flags.Local.LdFlags, cachePolicyFormat+policy)
}
// If the module does not have a profile, be conservative and limit cross TU inline
// limit to 5 LLVM IR instructions, to balance binary size increase and performance.
if !ctx.isPgoCompile() && !ctx.isAfdoCompile() {
flags.Local.LdFlags = append(flags.Local.LdFlags,
"-Wl,-plugin-opt,-import-instr-limit=5")
}
}
return flags
}
func (lto *lto) LTO(ctx BaseModuleContext) bool {
return lto.ThinLTO() || lto.FullLTO() || lto.DefaultThinLTO(ctx)
}
func (lto *lto) DefaultThinLTO(ctx BaseModuleContext) bool {
host := ctx.Host()
vndk := ctx.isVndk() // b/169217596
return GlobalThinLTO(ctx) && !lto.Never() && !host && !vndk
}
func (lto *lto) FullLTO() bool {
return lto != nil && Bool(lto.Properties.Lto.Full)
}
func (lto *lto) ThinLTO() bool {
return lto != nil && Bool(lto.Properties.Lto.Thin)
}
func (lto *lto) Never() bool {
return lto != nil && Bool(lto.Properties.Lto.Never)
}
func GlobalThinLTO(ctx android.BaseModuleContext) bool {
return ctx.Config().IsEnvTrue("GLOBAL_THINLTO")
}
// Propagate lto requirements down from binaries
func ltoDepsMutator(mctx android.TopDownMutatorContext) {
globalThinLTO := GlobalThinLTO(mctx)
if m, ok := mctx.Module().(*Module); ok {
full := m.lto.FullLTO()
thin := m.lto.ThinLTO()
never := m.lto.Never()
if full && thin {
mctx.PropertyErrorf("LTO", "FullLTO and ThinLTO are mutually exclusive")
}
mctx.WalkDeps(func(dep android.Module, parent android.Module) bool {
tag := mctx.OtherModuleDependencyTag(dep)
libTag, isLibTag := tag.(libraryDependencyTag)
// Do not recurse down non-static dependencies
if isLibTag {
if !libTag.static() {
return false
}
} else {
if tag != objDepTag && tag != reuseObjTag {
return false
}
}
if dep, ok := dep.(*Module); ok {
if full && !dep.lto.FullLTO() {
dep.lto.Properties.FullDep = true
}
if !globalThinLTO && thin && !dep.lto.ThinLTO() {
dep.lto.Properties.ThinDep = true
}
if globalThinLTO && never && !dep.lto.Never() {
dep.lto.Properties.NoLtoDep = true
}
}
// Recursively walk static dependencies
return true
})
}
}
// Create lto variants for modules that need them
func ltoMutator(mctx android.BottomUpMutatorContext) {
globalThinLTO := GlobalThinLTO(mctx)
if m, ok := mctx.Module().(*Module); ok && m.lto != nil {
// Create variations for LTO types required as static
// dependencies
variationNames := []string{""}
if m.lto.Properties.FullDep && !m.lto.FullLTO() {
variationNames = append(variationNames, "lto-full")
}
if !globalThinLTO && m.lto.Properties.ThinDep && !m.lto.ThinLTO() {
variationNames = append(variationNames, "lto-thin")
}
if globalThinLTO && m.lto.Properties.NoLtoDep && !m.lto.Never() {
variationNames = append(variationNames, "lto-none")
}
// Use correct dependencies if LTO property is explicitly set
// (mutually exclusive)
if m.lto.FullLTO() {
mctx.SetDependencyVariation("lto-full")
}
if !globalThinLTO && m.lto.ThinLTO() {
mctx.SetDependencyVariation("lto-thin")
}
// Never must be the last, it overrides Thin or Full.
if globalThinLTO && m.lto.Never() {
mctx.SetDependencyVariation("lto-none")
}
if len(variationNames) > 1 {
modules := mctx.CreateVariations(variationNames...)
for i, name := range variationNames {
variation := modules[i].(*Module)
// Default module which will be
// installed. Variation set above according to
// explicit LTO properties
if name == "" {
continue
}
// LTO properties for dependencies
if name == "lto-full" {
variation.lto.Properties.Lto.Full = proptools.BoolPtr(true)
}
if name == "lto-thin" {
variation.lto.Properties.Lto.Thin = proptools.BoolPtr(true)
}
if name == "lto-none" {
variation.lto.Properties.Lto.Never = proptools.BoolPtr(true)
}
variation.Properties.PreventInstall = true
variation.Properties.HideFromMake = true
variation.lto.Properties.FullDep = false
variation.lto.Properties.ThinDep = false
variation.lto.Properties.NoLtoDep = false
}
}
}
}