222 lines
7.1 KiB
Go
222 lines
7.1 KiB
Go
// Copyright 2017 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package cc
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import (
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"android/soong/android"
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)
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// LTO (link-time optimization) allows the compiler to optimize and generate
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// code for the entire module at link time, rather than per-compilation
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// unit. LTO is required for Clang CFI and other whole-program optimization
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// techniques. LTO also allows cross-compilation unit optimizations that should
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// result in faster and smaller code, at the expense of additional compilation
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// time.
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//
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// To properly build a module with LTO, the module and all recursive static
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// dependencies should be compiled with -flto which directs the compiler to emit
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// bitcode rather than native object files. These bitcode files are then passed
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// by the linker to the LLVM plugin for compilation at link time. Static
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// dependencies not built as bitcode will still function correctly but cannot be
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// optimized at link time and may not be compatible with features that require
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// LTO, such as CFI.
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//
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// This file adds support to soong to automatically propogate LTO options to a
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// new variant of all static dependencies for each module with LTO enabled.
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type LTOProperties struct {
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// Lto must violate capitialization style for acronyms so that it can be
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// referred to in blueprint files as "lto"
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Lto struct {
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Never *bool `android:"arch_variant"`
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Full *bool `android:"arch_variant"`
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Thin *bool `android:"arch_variant"`
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} `android:"arch_variant"`
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// Dep properties indicate that this module needs to be built with LTO
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// since it is an object dependency of an LTO module.
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FullDep bool `blueprint:"mutated"`
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ThinDep bool `blueprint:"mutated"`
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// Use clang lld instead of gnu ld.
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Use_clang_lld *bool
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}
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type lto struct {
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Properties LTOProperties
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}
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func (lto *lto) props() []interface{} {
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return []interface{}{<o.Properties}
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}
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func (lto *lto) begin(ctx BaseModuleContext) {
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if ctx.Config().IsEnvTrue("DISABLE_LTO") {
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lto.Properties.Lto.Never = boolPtr(true)
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}
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}
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func (lto *lto) deps(ctx BaseModuleContext, deps Deps) Deps {
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return deps
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}
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func (lto *lto) useClangLld(ctx BaseModuleContext) bool {
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if lto.Properties.Use_clang_lld != nil {
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return Bool(lto.Properties.Use_clang_lld)
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}
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return true
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}
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func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
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// TODO(b/131771163): Disable LTO when using explicit fuzzing configurations.
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// LTO breaks fuzzer builds.
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if inList("-fsanitize=fuzzer-no-link", flags.CFlags) {
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return flags
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}
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if lto.LTO() {
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var ltoFlag string
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if Bool(lto.Properties.Lto.Thin) {
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ltoFlag = "-flto=thin -fsplit-lto-unit"
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} else {
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ltoFlag = "-flto"
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}
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flags.CFlags = append(flags.CFlags, ltoFlag)
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flags.LdFlags = append(flags.LdFlags, ltoFlag)
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if ctx.Config().IsEnvTrue("USE_THINLTO_CACHE") && Bool(lto.Properties.Lto.Thin) && lto.useClangLld(ctx) {
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// Set appropriate ThinLTO cache policy
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cacheDirFormat := "-Wl,--thinlto-cache-dir="
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cacheDir := android.PathForOutput(ctx, "thinlto-cache").String()
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flags.LdFlags = append(flags.LdFlags, cacheDirFormat+cacheDir)
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// Limit the size of the ThinLTO cache to the lesser of 10% of available
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// disk space and 10GB.
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cachePolicyFormat := "-Wl,--thinlto-cache-policy="
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policy := "cache_size=10%:cache_size_bytes=10g"
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flags.LdFlags = append(flags.LdFlags, cachePolicyFormat+policy)
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}
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// If the module does not have a profile, be conservative and do not inline
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// or unroll loops during LTO, in order to prevent significant size bloat.
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if !ctx.isPgoCompile() {
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flags.LdFlags = append(flags.LdFlags, "-Wl,-plugin-opt,-inline-threshold=0")
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flags.LdFlags = append(flags.LdFlags, "-Wl,-plugin-opt,-unroll-threshold=0")
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}
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}
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return flags
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}
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// Can be called with a null receiver
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func (lto *lto) LTO() bool {
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if lto == nil || lto.Disabled() {
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return false
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}
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full := Bool(lto.Properties.Lto.Full)
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thin := Bool(lto.Properties.Lto.Thin)
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return full || thin
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}
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// Is lto.never explicitly set to true?
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func (lto *lto) Disabled() bool {
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return lto.Properties.Lto.Never != nil && *lto.Properties.Lto.Never
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}
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// Propagate lto requirements down from binaries
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func ltoDepsMutator(mctx android.TopDownMutatorContext) {
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if m, ok := mctx.Module().(*Module); ok && m.lto.LTO() {
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full := Bool(m.lto.Properties.Lto.Full)
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thin := Bool(m.lto.Properties.Lto.Thin)
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if full && thin {
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mctx.PropertyErrorf("LTO", "FullLTO and ThinLTO are mutually exclusive")
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}
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mctx.WalkDeps(func(dep android.Module, parent android.Module) bool {
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tag := mctx.OtherModuleDependencyTag(dep)
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switch tag {
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case StaticDepTag, staticExportDepTag, lateStaticDepTag, wholeStaticDepTag, objDepTag, reuseObjTag:
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if dep, ok := dep.(*Module); ok && dep.lto != nil &&
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!dep.lto.Disabled() {
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if full && !Bool(dep.lto.Properties.Lto.Full) {
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dep.lto.Properties.FullDep = true
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}
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if thin && !Bool(dep.lto.Properties.Lto.Thin) {
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dep.lto.Properties.ThinDep = true
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}
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}
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// Recursively walk static dependencies
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return true
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}
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// Do not recurse down non-static dependencies
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return false
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})
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}
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}
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// Create lto variants for modules that need them
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func ltoMutator(mctx android.BottomUpMutatorContext) {
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if m, ok := mctx.Module().(*Module); ok && m.lto != nil {
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// Create variations for LTO types required as static
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// dependencies
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variationNames := []string{""}
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if m.lto.Properties.FullDep && !Bool(m.lto.Properties.Lto.Full) {
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variationNames = append(variationNames, "lto-full")
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}
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if m.lto.Properties.ThinDep && !Bool(m.lto.Properties.Lto.Thin) {
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variationNames = append(variationNames, "lto-thin")
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}
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// Use correct dependencies if LTO property is explicitly set
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// (mutually exclusive)
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if Bool(m.lto.Properties.Lto.Full) {
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mctx.SetDependencyVariation("lto-full")
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}
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if Bool(m.lto.Properties.Lto.Thin) {
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mctx.SetDependencyVariation("lto-thin")
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}
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if len(variationNames) > 1 {
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modules := mctx.CreateVariations(variationNames...)
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for i, name := range variationNames {
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variation := modules[i].(*Module)
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// Default module which will be
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// installed. Variation set above according to
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// explicit LTO properties
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if name == "" {
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continue
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}
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// LTO properties for dependencies
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if name == "lto-full" {
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variation.lto.Properties.Lto.Full = boolPtr(true)
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variation.lto.Properties.Lto.Thin = boolPtr(false)
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}
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if name == "lto-thin" {
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variation.lto.Properties.Lto.Full = boolPtr(false)
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variation.lto.Properties.Lto.Thin = boolPtr(true)
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}
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variation.Properties.PreventInstall = true
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variation.Properties.HideFromMake = true
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variation.lto.Properties.FullDep = false
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variation.lto.Properties.ThinDep = false
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}
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}
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}
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}
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