builder: add optsize attribute while building the package

This simplifies future changes. While the move itself is very simple, it
required some other changes to a few transforms that create new
functions to add the optsize attribute manually. It also required
abstracting away the optimization level flags (based on the -opt flag)
so that it can easily be retrieved from the config object.

This commit does not impact binary size on baremetal and WebAssembly.
I've seen a few tests on linux/amd64 grow slightly in size, but I'm not
too worried about those.

9 files changed, 66 insertions, 33 deletions

diff --git a/builder/build.go b/builder/build.go
index 1a9ad9c1b..73981e71e 100644
--- a/builder/build.go
+++ b/builder/build.go
@@ -60,6 +60,7 @@ type packageAction struct {
 	CFlags          []string
 	FileHashes      map[string]string // hash of every file that's part of the package
 	Imports         map[string]string // map from imported package to action ID hash
+	SizeLevel       int               // LLVM optimization for size level (0-2)
 }
 
 // Build performs a single package to executable Go build. It takes in a package
@@ -127,6 +128,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 	var packageJobs []*compileJob
 	packageBitcodePaths := make(map[string]string)
 	packageActionIDs := make(map[string]string)
+	_, sizeLevel, _ := config.OptLevels()
 	for _, pkg := range lprogram.Sorted() {
 		pkg := pkg // necessary to avoid a race condition
 
@@ -141,6 +143,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 			CFlags:          pkg.CFlags,
 			FileHashes:      make(map[string]string, len(pkg.FileHashes)),
 			Imports:         make(map[string]string, len(pkg.Pkg.Imports())),
+			SizeLevel:       sizeLevel,
 		}
 		for filePath, hash := range pkg.FileHashes {
 			actionID.FileHashes[filePath] = hex.EncodeToString(hash)
@@ -206,6 +209,16 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 					return errors.New("verification error after interpreting " + pkgInit.Name())
 				}
 
+				if sizeLevel >= 2 {
+					// Set the "optsize" attribute to make slightly smaller
+					// binaries at the cost of some performance.
+					kind := llvm.AttributeKindID("optsize")
+					attr := mod.Context().CreateEnumAttribute(kind, 0)
+					for fn := mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
+						fn.AddFunctionAttr(attr)
+					}
+				}
+
 				// Serialize the LLVM module as a bitcode file.
 				// Write to a temporary path that is renamed to the destination
 				// file to avoid race conditions with other TinyGo invocatiosn
@@ -617,21 +630,8 @@ func optimizeProgram(mod llvm.Module, config *compileopts.Config) error {
 
 	// Optimization levels here are roughly the same as Clang, but probably not
 	// exactly.
-	var errs []error
-	switch config.Options.Opt {
-	case "none", "0":
-		errs = transform.Optimize(mod, config, 0, 0, 0) // -O0
-	case "1":
-		errs = transform.Optimize(mod, config, 1, 0, 0) // -O1
-	case "2":
-		errs = transform.Optimize(mod, config, 2, 0, 225) // -O2
-	case "s":
-		errs = transform.Optimize(mod, config, 2, 1, 225) // -Os
-	case "z":
-		errs = transform.Optimize(mod, config, 2, 2, 5) // -Oz, default
-	default:
-		return errors.New("unknown optimization level: -opt=" + config.Options.Opt)
-	}
+	optLevel, sizeLevel, inlinerThreshold := config.OptLevels()
+	errs := transform.Optimize(mod, config, optLevel, sizeLevel, inlinerThreshold)
 	if len(errs) > 0 {
 		return newMultiError(errs)
 	}
diff --git a/compileopts/config.go b/compileopts/config.go
index 50a8aeab6..58af7a8c5 100644
--- a/compileopts/config.go
+++ b/compileopts/config.go
@@ -118,6 +118,27 @@ func (c *Config) Scheduler() string {
 	return "coroutines"
 }
 
+// OptLevels returns the optimization level (0-2), size level (0-2), and inliner
+// threshold as used in the LLVM optimization pipeline.
+func (c *Config) OptLevels() (optLevel, sizeLevel int, inlinerThreshold uint) {
+	switch c.Options.Opt {
+	case "none", "0":
+		return 0, 0, 0 // -O0
+	case "1":
+		return 1, 0, 0 // -O1
+	case "2":
+		return 2, 0, 225 // -O2
+	case "s":
+		return 2, 1, 225 // -Os
+	case "z":
+		return 2, 2, 5 // -Oz, default
+	default:
+		// This is not shown to the user: valid choices are already checked as
+		// part of Options.Verify(). It is here as a sanity check.
+		panic("unknown optimization level: -opt=" + c.Options.Opt)
+	}
+}
+
 // FuncImplementation picks an appropriate func value implementation for the
 // target.
 func (c *Config) FuncImplementation() string {
diff --git a/compileopts/options.go b/compileopts/options.go
index f5f5a222d..d1c7c6edc 100644
--- a/compileopts/options.go
+++ b/compileopts/options.go
@@ -10,6 +10,7 @@ var (
 	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
 	validPrintSizeOptions     = []string{"none", "short", "full"}
 	validPanicStrategyOptions = []string{"print", "trap"}
+	validOptOptions           = []string{"none", "0", "1", "2", "s", "z"}
 )
 
 // Options contains extra options to give to the compiler. These options are
@@ -73,6 +74,12 @@ func (o *Options) Verify() error {
 		}
 	}
 
+	if o.Opt != "" {
+		if !isInArray(validOptOptions, o.Opt) {
+			return fmt.Errorf("invalid -opt=%s: valid values are %s", o.Opt, strings.Join(validOptOptions, ", "))
+		}
+	}
+
 	return nil
 }
 
diff --git a/transform/interface-lowering.go b/transform/interface-lowering.go
index 56956a39a..e8b6deecf 100644
--- a/transform/interface-lowering.go
+++ b/transform/interface-lowering.go
@@ -133,6 +133,7 @@ func (itf *interfaceInfo) id() string {
 // should be seen as a regular function call (see LowerInterfaces).
 type lowerInterfacesPass struct {
 	mod         llvm.Module
+	sizeLevel   int // LLVM optimization size level, 1 means -opt=s and 2 means -opt=z
 	builder     llvm.Builder
 	ctx         llvm.Context
 	uintptrType llvm.Type
@@ -145,9 +146,10 @@ type lowerInterfacesPass struct {
 // emitted by the compiler as higher-level intrinsics. They need some lowering
 // before LLVM can work on them. This is done so that a few cleanup passes can
 // run before assigning the final type codes.
-func LowerInterfaces(mod llvm.Module) error {
+func LowerInterfaces(mod llvm.Module, sizeLevel int) error {
 	p := &lowerInterfacesPass{
 		mod:         mod,
+		sizeLevel:   sizeLevel,
 		builder:     mod.Context().NewBuilder(),
 		ctx:         mod.Context(),
 		uintptrType: mod.Context().IntType(llvm.NewTargetData(mod.DataLayout()).PointerSize() * 8),
@@ -594,6 +596,9 @@ func (p *lowerInterfacesPass) createInterfaceImplementsFunc(itf *interfaceInfo)
 	fn := itf.assertFunc
 	fn.SetLinkage(llvm.InternalLinkage)
 	fn.SetUnnamedAddr(true)
+	if p.sizeLevel >= 2 {
+		fn.AddFunctionAttr(p.ctx.CreateEnumAttribute(llvm.AttributeKindID("optsize"), 0))
+	}
 
 	// TODO: debug info
 
@@ -653,6 +658,9 @@ func (p *lowerInterfacesPass) createInterfaceMethodFunc(itf *interfaceInfo, sign
 	fn := itf.methodFuncs[signature]
 	fn.SetLinkage(llvm.InternalLinkage)
 	fn.SetUnnamedAddr(true)
+	if p.sizeLevel >= 2 {
+		fn.AddFunctionAttr(p.ctx.CreateEnumAttribute(llvm.AttributeKindID("optsize"), 0))
+	}
 
 	// TODO: debug info
 
diff --git a/transform/interface-lowering_test.go b/transform/interface-lowering_test.go
index f3652cc90..e1c3c2dcc 100644
--- a/transform/interface-lowering_test.go
+++ b/transform/interface-lowering_test.go
@@ -9,7 +9,7 @@ import (
 func TestInterfaceLowering(t *testing.T) {
 	t.Parallel()
 	testTransform(t, "testdata/interface", func(mod llvm.Module) {
-		err := LowerInterfaces(mod)
+		err := LowerInterfaces(mod, 0)
 		if err != nil {
 			t.Error(err)
 		}
diff --git a/transform/interrupt.go b/transform/interrupt.go
index 1c3247d5e..d5d7d47e9 100644
--- a/transform/interrupt.go
+++ b/transform/interrupt.go
@@ -22,7 +22,7 @@ import (
 // simply call the registered handlers. This might seem like it causes extra
 // overhead, but in fact inlining and const propagation will eliminate most if
 // not all of that.
-func LowerInterrupts(mod llvm.Module) []error {
+func LowerInterrupts(mod llvm.Module, sizeLevel int) []error {
 	var errs []error
 
 	// Discover interrupts. The runtime/interrupt.Register call is a compiler
@@ -182,6 +182,9 @@ func LowerInterrupts(mod llvm.Module) []error {
 		// Create the wrapper function which is the actual interrupt handler
 		// that is inserted in the interrupt vector.
 		fn.SetUnnamedAddr(true)
+		if sizeLevel >= 2 {
+			fn.AddFunctionAttr(ctx.CreateEnumAttribute(llvm.AttributeKindID("optsize"), 0))
+		}
 		fn.SetSection(".text." + name)
 		if isSoftwareVectored {
 			fn.SetLinkage(llvm.InternalLinkage)
diff --git a/transform/interrupt_test.go b/transform/interrupt_test.go
index 00a199063..60d83da15 100644
--- a/transform/interrupt_test.go
+++ b/transform/interrupt_test.go
@@ -11,7 +11,7 @@ func TestInterruptLowering(t *testing.T) {
 	for _, subtest := range []string{"avr", "cortexm"} {
 		t.Run(subtest, func(t *testing.T) {
 			testTransform(t, "testdata/interrupt-"+subtest, func(mod llvm.Module) {
-				errs := LowerInterrupts(mod)
+				errs := LowerInterrupts(mod, 0)
 				if len(errs) != 0 {
 					t.Fail()
 					for _, err := range errs {
diff --git a/transform/optimizer.go b/transform/optimizer.go
index e10144b92..108219106 100644
--- a/transform/optimizer.go
+++ b/transform/optimizer.go
@@ -76,12 +76,12 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 		OptimizeStringToBytes(mod)
 		OptimizeReflectImplements(mod)
 		OptimizeAllocs(mod)
-		err := LowerInterfaces(mod)
+		err := LowerInterfaces(mod, sizeLevel)
 		if err != nil {
 			return []error{err}
 		}
 
-		errs := LowerInterrupts(mod)
+		errs := LowerInterrupts(mod, sizeLevel)
 		if len(errs) > 0 {
 			return errs
 		}
@@ -102,14 +102,14 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 
 	} else {
 		// Must be run at any optimization level.
-		err := LowerInterfaces(mod)
+		err := LowerInterfaces(mod, sizeLevel)
 		if err != nil {
 			return []error{err}
 		}
 		if config.FuncImplementation() == "switch" {
 			LowerFuncValues(mod)
 		}
-		errs := LowerInterrupts(mod)
+		errs := LowerInterrupts(mod, sizeLevel)
 		if len(errs) > 0 {
 			return errs
 		}
@@ -153,16 +153,6 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 		return []error{errors.New("optimizations caused a verification failure")}
 	}
 
-	if sizeLevel >= 2 {
-		// Set the "optsize" attribute to make slightly smaller binaries at the
-		// cost of some performance.
-		kind := llvm.AttributeKindID("optsize")
-		attr := mod.Context().CreateEnumAttribute(kind, 0)
-		for fn := mod.FirstFunction(); !fn.IsNil(); fn = llvm.NextFunction(fn) {
-			fn.AddFunctionAttr(attr)
-		}
-	}
-
 	// After TinyGo-specific transforms have finished, undo exporting these functions.
 	for _, name := range getFunctionsUsedInTransforms(config) {
 		fn := mod.NamedFunction(name)
diff --git a/transform/wasm-abi.go b/transform/wasm-abi.go
index 0c3af9a3d..85e419145 100644
--- a/transform/wasm-abi.go
+++ b/transform/wasm-abi.go
@@ -73,6 +73,10 @@ func ExternalInt64AsPtr(mod llvm.Module) error {
 		fn.SetName(name + "$i64wrap")
 		externalFnType := llvm.FunctionType(returnType, paramTypes, fnType.IsFunctionVarArg())
 		externalFn := llvm.AddFunction(mod, name, externalFnType)
+		optsize := fn.GetEnumFunctionAttribute(llvm.AttributeKindID("optsize"))
+		if !optsize.IsNil() {
+			fn.AddFunctionAttr(optsize)
+		}
 
 		if fn.IsDeclaration() {
 			// Just a declaration: the definition doesn't exist on the Go side