compiler,transform: move interface lowering to transform package

transform/llvm.go

@@ -1,12 +1,17 @@
 package transform
 
 import (
+	"reflect"
+
 	"tinygo.org/x/go-llvm"
 )
 
 // Return a list of values (actually, instructions) where this value is used as
 // an operand.
 func getUses(value llvm.Value) []llvm.Value {
+	if value.IsNil() {
+		return nil
+	}
 	var uses []llvm.Value
 	use := value.FirstUse()
 	for !use.IsNil() {
@@ -15,3 +20,48 @@ func getUses(value llvm.Value) []llvm.Value {
 	}
 	return uses
 }
+
+// makeGlobalArray creates a new LLVM global with the given name and integers as
+// contents, and returns the global.
+// Note that it is left with the default linkage etc., you should set
+// linkage/constant/etc properties yourself.
+func makeGlobalArray(mod llvm.Module, bufItf interface{}, name string, elementType llvm.Type) llvm.Value {
+	buf := reflect.ValueOf(bufItf)
+	globalType := llvm.ArrayType(elementType, buf.Len())
+	global := llvm.AddGlobal(mod, globalType, name)
+	value := llvm.Undef(globalType)
+	for i := 0; i < buf.Len(); i++ {
+		ch := buf.Index(i).Uint()
+		value = llvm.ConstInsertValue(value, llvm.ConstInt(elementType, ch, false), []uint32{uint32(i)})
+	}
+	global.SetInitializer(value)
+	return global
+}
+
+// getGlobalBytes returns the slice contained in the array of the provided
+// global. It can recover the bytes originally created using makeGlobalArray, if
+// makeGlobalArray was given a byte slice.
+func getGlobalBytes(global llvm.Value) []byte {
+	value := global.Initializer()
+	buf := make([]byte, value.Type().ArrayLength())
+	for i := range buf {
+		buf[i] = byte(llvm.ConstExtractValue(value, []uint32{uint32(i)}).ZExtValue())
+	}
+	return buf
+}
+
+// replaceGlobalByteWithArray replaces a global integer type in the module with
+// an integer array, using a GEP to make the types match. It is a convenience
+// function used for creating reflection sidetables, for example.
+func replaceGlobalIntWithArray(mod llvm.Module, name string, buf interface{}) llvm.Value {
+	oldGlobal := mod.NamedGlobal(name)
+	global := makeGlobalArray(mod, buf, name+".tmp", oldGlobal.Type().ElementType())
+	gep := llvm.ConstGEP(global, []llvm.Value{
+		llvm.ConstInt(mod.Context().Int32Type(), 0, false),
+		llvm.ConstInt(mod.Context().Int32Type(), 0, false),
+	})
+	oldGlobal.ReplaceAllUsesWith(gep)
+	oldGlobal.EraseFromParentAsGlobal()
+	global.SetName(name)
+	return global
+}