Add Global ThinLTO option (2nd try)

Instead of making everything into ThinLTO variant by default (it works
but many Soong tests don't like this, and got bit rot due to lack of
active builder for this configuration), let the default option be
ThinLTO and no LTO be a special variant.

Test: m GLOBAL_THINLTO=true
Test: m
Bug: 195134194
Change-Id: I2fd98061ba55eba1fdfdd056fb2f8c2051fd2553

cc/lto.go

@@ -51,6 +51,7 @@ type LTOProperties struct {
 	// 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
@@ -70,15 +71,6 @@ func (lto *lto) props() []interface{} {
 func (lto *lto) begin(ctx BaseModuleContext) {
 	if ctx.Config().IsEnvTrue("DISABLE_LTO") {
 		lto.Properties.Lto.Never = proptools.BoolPtr(true)
-	} else if ctx.Config().IsEnvTrue("GLOBAL_THINLTO") {
-		staticLib := ctx.static() && !ctx.staticBinary()
-		hostBin := ctx.Host()
-		vndk := ctx.isVndk() // b/169217596
-		if !staticLib && !hostBin && !vndk {
-			if !lto.Never() && !lto.FullLTO() {
-				lto.Properties.Lto.Thin = proptools.BoolPtr(true)
-			}
-		}
 	}
 }
 
@@ -96,22 +88,27 @@ func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
 		return flags
 	}
 
-	if lto.LTO() {
+	if lto.LTO(ctx) {
-		var ltoFlag string
+		var ltoCFlag string
+		var ltoLdFlag string
 		if lto.ThinLTO() {
-			ltoFlag = "-flto=thin -fsplit-lto-unit"
+			ltoCFlag = "-flto=thin -fsplit-lto-unit"
+		} else if lto.FullLTO() {
+			ltoCFlag = "-flto"
 		} else {
-			ltoFlag = "-flto"
+			ltoCFlag = "-flto=thin -fsplit-lto-unit"
+			ltoLdFlag = "-Wl,--lto-O0"
 		}
 
-		flags.Local.CFlags = append(flags.Local.CFlags, ltoFlag)
+		flags.Local.CFlags = append(flags.Local.CFlags, ltoCFlag)
-		flags.Local.LdFlags = append(flags.Local.LdFlags, ltoFlag)
+		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.ThinLTO() && ctx.Config().IsEnvTrue("USE_THINLTO_CACHE") && lto.useClangLld(ctx) {
+		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()
@@ -134,33 +131,40 @@ func (lto *lto) flags(ctx BaseModuleContext, flags Flags) Flags {
 	return flags
 }
 
-// Can be called with a null receiver
+func (lto *lto) LTO(ctx BaseModuleContext) bool {
-func (lto *lto) LTO() bool {
+	return lto.ThinLTO() || lto.FullLTO() || lto.DefaultThinLTO(ctx)
-	if lto == nil || lto.Never() {
+}
-		return false
-	}
 
-	return lto.FullLTO() || lto.ThinLTO()
+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 Bool(lto.Properties.Lto.Full)
+	return lto != nil && Bool(lto.Properties.Lto.Full)
 }
 
 func (lto *lto) ThinLTO() bool {
-	return Bool(lto.Properties.Lto.Thin)
+	return lto != nil && Bool(lto.Properties.Lto.Thin)
 }
 
-// Is lto.never explicitly set to true?
 func (lto *lto) Never() bool {
-	return Bool(lto.Properties.Lto.Never)
+	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) {
-	if m, ok := mctx.Module().(*Module); ok && m.lto.LTO() {
+	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")
 		}
@@ -180,14 +184,16 @@ func ltoDepsMutator(mctx android.TopDownMutatorContext) {
 				}
 			}
 
-			if dep, ok := dep.(*Module); ok && dep.lto != nil &&
+			if dep, ok := dep.(*Module); ok {
-				!dep.lto.Never() {
 				if full && !dep.lto.FullLTO() {
 					dep.lto.Properties.FullDep = true
 				}
-				if thin && !dep.lto.ThinLTO() {
+				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
@@ -198,6 +204,8 @@ func ltoDepsMutator(mctx android.TopDownMutatorContext) {
 
 // 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
@@ -205,18 +213,25 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 		if m.lto.Properties.FullDep && !m.lto.FullLTO() {
 			variationNames = append(variationNames, "lto-full")
 		}
-		if m.lto.Properties.ThinDep && !m.lto.ThinLTO() {
+		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 m.lto.ThinLTO() {
+		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...)
@@ -232,16 +247,18 @@ func ltoMutator(mctx android.BottomUpMutatorContext) {
 				// LTO properties for dependencies
 				if name == "lto-full" {
 					variation.lto.Properties.Lto.Full = proptools.BoolPtr(true)
-					variation.lto.Properties.Lto.Thin = proptools.BoolPtr(false)
 				}
 				if name == "lto-thin" {
-					variation.lto.Properties.Lto.Full = proptools.BoolPtr(false)
 					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
 			}
 		}
 	}