efc36678a9
This partially reverts commit 1281b99495.
Bug: b/282584808, b/254713216
Reason for revert: LTO can be enabled as emultated tls is now globally disabled https://android-review.git.corp.google.com/c/platform/build/soong/+/2431153
Change-Id: I66c83b1116550179043490a11f66b8630c0e6b1b
277 lines
8.9 KiB
Go
277 lines
8.9 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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"github.com/google/blueprint/proptools"
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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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FullEnabled bool `blueprint:"mutated"`
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ThinEnabled bool `blueprint:"mutated"`
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NoLtoEnabled bool `blueprint:"mutated"`
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FullDep bool `blueprint:"mutated"`
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ThinDep bool `blueprint:"mutated"`
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NoLtoDep 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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// Use -fwhole-program-vtables cflag.
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Whole_program_vtables *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.NoLtoEnabled = true
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}
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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.Local.CFlags) {
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return flags
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}
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if lto.LTO(ctx) {
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var ltoCFlag string
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var ltoLdFlag string
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if lto.ThinLTO() {
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ltoCFlag = "-flto=thin -fsplit-lto-unit"
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} else if lto.FullLTO() {
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ltoCFlag = "-flto"
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} else {
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ltoCFlag = "-flto=thin -fsplit-lto-unit"
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ltoLdFlag = "-Wl,--lto-O0"
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}
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flags.Local.CFlags = append(flags.Local.CFlags, ltoCFlag)
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flags.Local.AsFlags = append(flags.Local.AsFlags, ltoCFlag)
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flags.Local.LdFlags = append(flags.Local.LdFlags, ltoCFlag)
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flags.Local.LdFlags = append(flags.Local.LdFlags, ltoLdFlag)
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if Bool(lto.Properties.Whole_program_vtables) {
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flags.Local.CFlags = append(flags.Local.CFlags, "-fwhole-program-vtables")
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}
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if (lto.DefaultThinLTO(ctx) || lto.ThinLTO()) && ctx.Config().IsEnvTrue("USE_THINLTO_CACHE") && 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.Local.LdFlags = append(flags.Local.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.Local.LdFlags = append(flags.Local.LdFlags, cachePolicyFormat+policy)
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}
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// If the module does not have a profile, be conservative and limit cross TU inline
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// limit to 5 LLVM IR instructions, to balance binary size increase and performance.
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if !ctx.isPgoCompile() && !ctx.isAfdoCompile() {
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flags.Local.LdFlags = append(flags.Local.LdFlags,
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"-Wl,-plugin-opt,-import-instr-limit=5")
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}
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}
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return flags
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}
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func (lto *lto) LTO(ctx BaseModuleContext) bool {
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return lto.ThinLTO() || lto.FullLTO() || lto.DefaultThinLTO(ctx)
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}
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func (lto *lto) DefaultThinLTO(ctx BaseModuleContext) bool {
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// LP32 has many subtle issues and less test coverage.
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lib32 := ctx.Arch().ArchType.Multilib == "lib32"
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// CFI enables full LTO.
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cfi := ctx.isCfi()
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// Performance and binary size are less important for host binaries and tests.
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host := ctx.Host()
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test := ctx.testBinary() || ctx.testLibrary()
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// FIXME: ThinLTO for VNDK produces different output.
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// b/169217596
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vndk := ctx.isVndk()
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return GlobalThinLTO(ctx) && !lto.Never() && !lib32 && !cfi && !host && !test && !vndk
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}
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func (lto *lto) FullLTO() bool {
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return lto != nil && (proptools.Bool(lto.Properties.Lto.Full) || lto.Properties.FullEnabled)
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}
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func (lto *lto) ThinLTO() bool {
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return lto != nil && (proptools.Bool(lto.Properties.Lto.Thin) || lto.Properties.ThinEnabled)
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}
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func (lto *lto) Never() bool {
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return lto != nil && (proptools.Bool(lto.Properties.Lto.Never) || lto.Properties.NoLtoEnabled)
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}
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func GlobalThinLTO(ctx android.BaseModuleContext) bool {
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return ctx.Config().IsEnvTrue("GLOBAL_THINLTO")
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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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globalThinLTO := GlobalThinLTO(mctx)
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if m, ok := mctx.Module().(*Module); ok {
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full := m.lto.FullLTO()
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thin := m.lto.ThinLTO()
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never := m.lto.Never()
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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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libTag, isLibTag := tag.(libraryDependencyTag)
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// Do not recurse down non-static dependencies
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if isLibTag {
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if !libTag.static() {
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return false
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}
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} else {
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if tag != objDepTag && tag != reuseObjTag {
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return false
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}
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}
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if dep, ok := dep.(*Module); ok {
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if full && !dep.lto.FullLTO() {
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dep.lto.Properties.FullDep = true
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}
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if !globalThinLTO && thin && !dep.lto.ThinLTO() {
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dep.lto.Properties.ThinDep = true
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}
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if globalThinLTO && never && !dep.lto.Never() {
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dep.lto.Properties.NoLtoDep = 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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}
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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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globalThinLTO := GlobalThinLTO(mctx)
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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 && !m.lto.FullLTO() {
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variationNames = append(variationNames, "lto-full")
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}
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if !globalThinLTO && m.lto.Properties.ThinDep && !m.lto.ThinLTO() {
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variationNames = append(variationNames, "lto-thin")
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}
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if globalThinLTO && m.lto.Properties.NoLtoDep && !m.lto.Never() {
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variationNames = append(variationNames, "lto-none")
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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 m.lto.FullLTO() {
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mctx.SetDependencyVariation("lto-full")
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}
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if !globalThinLTO && m.lto.ThinLTO() {
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mctx.SetDependencyVariation("lto-thin")
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}
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// Never must be the last, it overrides Thin or Full.
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if globalThinLTO && m.lto.Never() {
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mctx.SetDependencyVariation("lto-none")
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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.FullEnabled = true
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}
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if name == "lto-thin" {
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variation.lto.Properties.ThinEnabled = true
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}
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if name == "lto-none" {
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variation.lto.Properties.NoLtoEnabled = 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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variation.lto.Properties.NoLtoDep = false
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}
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}
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}
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}
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