cl: builtin llgo tag

cl/_testdata/llgotag/in.go

@@ -0,0 +1,7 @@
+//go:build llgo
+// +build llgo
+
+package llgotag
+
+func Foo() {
+}

cl/_testdata/llgotag/out.ll

@@ -0,0 +1,22 @@
+; ModuleID = 'llgotag'
+source_filename = "llgotag"
+
+@"llgotag.init$guard" = global i1 false, align 1
+
+define void @llgotag.Foo() {
+_llgo_0:
+  ret void
+}
+
+define void @llgotag.init() {
+_llgo_0:
+  %0 = load i1, ptr @"llgotag.init$guard", align 1
+  br i1 %0, label %_llgo_2, label %_llgo_1
+
+_llgo_1:                                          ; preds = %_llgo_0
+  store i1 true, ptr @"llgotag.init$guard", align 1
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}

internal/build/build.go

@@ -121,6 +121,7 @@ const (
 
 func Do(args []string, conf *Config) {
 	flags, patterns, verbose := ParseArgs(args, buildFlags)
+	flags = append(flags, "-tags", "llgo")
 	cfg := &packages.Config{
 		Mode:       loadSyntax | packages.NeedDeps | packages.NeedModule | packages.NeedExportFile,
 		BuildFlags: flags,