From 0713e336d9898aad7c161e92b8d27096142b64b6 Mon Sep 17 00:00:00 2001
From: Yi Kong <yikong@google.com>
Date: Wed, 31 May 2023 14:15:22 +0900
Subject: [PATCH] Remove Full LTO support

We do not have any more projects directly depending on Full LTO (except
CFI which manages their own LTO flags), remove full LTO support from the
build system.

Test: presubmit
Bug: 169004486
Change-Id: I8d6b7999d716158b5d8fe34b2f197653d7bae8dd
---
 cc/lto.go | 32 +++-----------------------------
 1 file changed, 3 insertions(+), 29 deletions(-)

diff --git a/cc/lto.go b/cc/lto.go
index be8fc56ca..a8bed235f 100644
--- a/cc/lto.go
+++ b/cc/lto.go
@@ -43,16 +43,13 @@ type LTOProperties struct {
 	// 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.
-	FullEnabled  bool `blueprint:"mutated"`
 	ThinEnabled  bool `blueprint:"mutated"`
 	NoLtoEnabled bool `blueprint:"mutated"`
-	FullDep      bool `blueprint:"mutated"`
 	ThinDep      bool `blueprint:"mutated"`
 	NoLtoDep     bool `blueprint:"mutated"`
 
@@ -86,8 +83,6 @@ func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
 		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"
@@ -126,13 +121,13 @@ func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
 }
 
 func (lto *lto) LTO(ctx BaseModuleContext) bool {
-	return lto.ThinLTO() || lto.FullLTO() || lto.DefaultThinLTO(ctx)
+	return lto.ThinLTO() || lto.DefaultThinLTO(ctx)
 }
 
 func (lto *lto) DefaultThinLTO(ctx BaseModuleContext) bool {
 	// LP32 has many subtle issues and less test coverage.
 	lib32 := ctx.Arch().ArchType.Multilib == "lib32"
-	// CFI enables full LTO.
+	// CFI adds LTO flags by itself.
 	cfi := ctx.isCfi()
 	// Performance and binary size are less important for host binaries and tests.
 	host := ctx.Host()
@@ -143,10 +138,6 @@ func (lto *lto) DefaultThinLTO(ctx BaseModuleContext) bool {
 	return GlobalThinLTO(ctx) && !lto.Never() && !lib32 && !cfi && !host && !test && !vndk
 }
 
-func (lto *lto) FullLTO() bool {
-	return lto != nil && (proptools.Bool(lto.Properties.Lto.Full) || lto.Properties.FullEnabled)
-}
-
 func (lto *lto) ThinLTO() bool {
 	return lto != nil && (proptools.Bool(lto.Properties.Lto.Thin) || lto.Properties.ThinEnabled)
 }
@@ -164,12 +155,8 @@ 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)
@@ -187,9 +174,6 @@ func ltoDepsMutator(mctx android.TopDownMutatorContext) {
 			}
 
 			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
 				}
@@ -212,9 +196,6 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 		// 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")
 		}
@@ -224,13 +205,10 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 
 		// 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.
+		// Never must be the last, it overrides Thin.
 		if globalThinLTO && m.lto.Never() {
 			mctx.SetDependencyVariation("lto-none")
 		}
@@ -247,9 +225,6 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 				}
 
 				// LTO properties for dependencies
-				if name == "lto-full" {
-					variation.lto.Properties.FullEnabled = true
-				}
 				if name == "lto-thin" {
 					variation.lto.Properties.ThinEnabled = true
 				}
@@ -258,7 +233,6 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 				}
 				variation.Properties.PreventInstall = true
 				variation.Properties.HideFromMake = true
-				variation.lto.Properties.FullDep = false
 				variation.lto.Properties.ThinDep = false
 				variation.lto.Properties.NoLtoDep = false
 			}