compiler: add //go:inline pragma

compiler/compiler.go

@@ -828,6 +828,14 @@ func (c *Compiler) parseFunc(frame *Frame) {
 		frame.fn.LLVMFn.SetFunctionCallConv(85) // CallingConv::AVR_SIGNAL
 	}
 
+	// Some functions have a pragma controlling the inlining level.
+	switch frame.fn.Inline() {
+	case ir.InlineHint:
+		// Add LLVM inline hint to functions with //go:inline pragma.
+		inline := c.ctx.CreateEnumAttribute(llvm.AttributeKindID("inlinehint"), 0)
+		frame.fn.LLVMFn.AddFunctionAttr(inline)
+	}
+
 	// Add debug info, if needed.
 	if c.Debug {
 		if frame.fn.Synthetic == "package initializer" {

ir/ir.go

@@ -33,11 +33,12 @@ type Program struct {
 type Function struct {
 	*ssa.Function
 	LLVMFn    llvm.Value
-	linkName  string // go:linkname, go:export, go:interrupt
-	exported  bool   // go:export
-	nobounds  bool   // go:nobounds
-	flag      bool   // used by dead code elimination
-	interrupt bool   // go:interrupt
+	linkName  string     // go:linkname, go:export, go:interrupt
+	exported  bool       // go:export
+	nobounds  bool       // go:nobounds
+	flag      bool       // used by dead code elimination
+	interrupt bool       // go:interrupt
+	inline    InlineType // go:inline
 }
 
 // Global variable, possibly constant.
@@ -69,6 +70,21 @@ type Interface struct {
 	Type *types.Interface
 }
 
+type InlineType int
+
+// How much to inline.
+const (
+	// Default behavior. The compiler decides for itself whether any given
+	// function will be inlined. Whether any function is inlined depends on the
+	// optimization level.
+	InlineDefault InlineType = iota
+
+	// Inline hint, just like the C inline keyword (signalled using
+	// //go:inline). The compiler will be more likely to inline this function,
+	// but it is not a guarantee.
+	InlineHint
+)
+
 // Create and initialize a new *Program from a *ssa.Program.
 func NewProgram(lprogram *loader.Program, mainPath string) *Program {
 	comments := map[string]*ast.CommentGroup{}
@@ -279,6 +295,8 @@ func (f *Function) parsePragmas() {
 				}
 				f.linkName = parts[1]
 				f.exported = true
+			case "//go:inline":
+				f.inline = InlineHint
 			case "//go:interrupt":
 				if len(parts) != 2 {
 					continue
@@ -332,6 +350,11 @@ func (f *Function) IsInterrupt() bool {
 	return f.interrupt
 }
 
+// Return the inline directive of this function.
+func (f *Function) Inline() InlineType {
+	return f.inline
+}
+
 // Return the link name for this function.
 func (f *Function) LinkName() string {
 	if f.linkName != "" {