vkFuncDecl, vkFuncPtr, vkClosure; callback example

cl/_testrt/callback/out.ll

@@ -0,0 +1,49 @@
+; ModuleID = 'main'
+source_filename = "main"
+
+@"main.init$guard" = global ptr null
+@0 = private unnamed_addr constant [17 x i8] c"Hello, callback\0A\00", align 1
+
+define void @main.callback({ ptr, ptr } %0) {
+_llgo_0:
+  %1 = extractvalue { ptr, ptr } %0, 0
+  call void %1()
+  ret void
+}
+
+define void @main.init() {
+_llgo_0:
+  %0 = load i1, ptr @"main.init$guard", align 1
+  br i1 %0, label %_llgo_2, label %_llgo_1
+
+_llgo_1:                                          ; preds = %_llgo_0
+  store i1 true, ptr @"main.init$guard", align 1
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+define void @main() {
+_llgo_0:
+  call void @"github.com/goplus/llgo/internal/runtime.init"()
+  call void @main.init()
+  %0 = alloca { ptr, ptr }, align 8
+  %1 = getelementptr inbounds { ptr, ptr }, ptr %0, i32 0, i32 0
+  store ptr @"main.main$1", ptr %1, align 8
+  %2 = getelementptr inbounds { ptr, ptr }, ptr %0, i32 0, i32 1
+  store ptr null, ptr %2, align 8
+  %3 = load { ptr, ptr }, ptr %0, align 8
+  call void @main.callback({ ptr, ptr } %3)
+  ret void
+}
+
+declare void @"github.com/goplus/llgo/internal/runtime.init"()
+
+define void @"main.main$1"() {
+_llgo_0:
+  %0 = call i32 (ptr, ...) @printf(ptr @0)
+  ret void
+}
+
+declare i32 @printf(ptr, ...)