core: check registers numbers, fix fallback mode

jadx-core/src/main/java/jadx/core/codegen/ClassGen.java

@@ -302,7 +302,7 @@ public class ClassGen {
 				}
 			}
 			MethodGen mthGen;
-			if (badCode || mth.contains(AType.JADX_ERROR)) {
+			if (badCode || mth.contains(AType.JADX_ERROR) || fallback) {
 				mthGen = MethodGen.getFallbackMethodGen(mth);
 			} else {
 				mthGen = new MethodGen(this, mth);
@@ -313,7 +313,11 @@ public class ClassGen {
 			code.add('{');
 			code.incIndent();
 			insertSourceFileInfo(code, mth);
-			mthGen.addInstructions(code);
+			if (fallback) {
+				mthGen.addFallbackMethodCode(code);
+			} else {
+				mthGen.addInstructions(code);
+			}
 			code.decIndent();
 			code.startLine('}');
 		}
@@ -535,7 +539,7 @@ public class ClassGen {
 	private void insertSourceFileInfo(CodeWriter code, AttrNode node) {
 		SourceFileAttr sourceFileAttr = node.get(AType.SOURCE_FILE);
 		if (sourceFileAttr != null) {
-			code.startLine("// compiled from: ").add(sourceFileAttr.getFileName());
+			code.startLine("/* compiled from: ").add(sourceFileAttr.getFileName()).add(" */");
 		}
 	}
 

jadx-core/src/main/java/jadx/core/codegen/NameGen.java

@@ -70,7 +70,7 @@ public class NameGen {
 
 	public String useArg(RegisterArg arg) {
 		String name = arg.getName();
-		if (name == null) {
+		if (name == null || fallback) {
 			return getFallbackName(arg);
 		}
 		return name;
@@ -117,10 +117,7 @@ public class NameGen {
 	private String getFallbackName(RegisterArg arg) {
 		String name = arg.getName();
 		String base = "r" + arg.getRegNum();
-		if (name != null && !name.equals("this")) {
-			return base + "_" + name;
-		}
-		return base;
+		return name != null ? base + "_" + name : base;
 	}
 
 	private static String makeNameForType(ArgType type) {

jadx-core/src/main/java/jadx/core/dex/nodes/MethodNode.java

@@ -114,6 +114,26 @@ public class MethodNode extends LineAttrNode implements ILoadable {
 		}
 	}
 
+	public void checkInstructions() {
+		List<RegisterArg> list = new ArrayList<RegisterArg>();
+		for (InsnNode insnNode : instructions) {
+			if (insnNode == null) {
+				continue;
+			}
+			list.clear();
+			RegisterArg resultArg = insnNode.getResult();
+			if (resultArg != null) {
+				list.add(resultArg);
+			}
+			insnNode.getRegisterArgs(list);
+			for (int i = 0, listSize = list.size(); i < listSize; i++) {
+				if (list.get(i).getRegNum() >= regsCount) {
+					throw new JadxRuntimeException("Incorrect register number in instruction: " + insnNode);
+				}
+			}
+		}
+	}
+
 	private void initMethodTypes() {
 		if (!parseSignature()) {
 			retType = mthInfo.getReturnType();

jadx-core/src/main/java/jadx/core/dex/visitors/BlockMakerVisitor.java

@@ -45,6 +45,8 @@ public class BlockMakerVisitor extends AbstractVisitor {
 		if (mth.isNoCode()) {
 			return;
 		}
+		mth.checkInstructions();
+
 		mth.initBasicBlocks();
 		splitBasicBlocks(mth);
 		processBlocksTree(mth);

jadx-core/src/main/java/jadx/core/dex/visitors/DepthTraversal.java

@@ -1,5 +1,6 @@
 package jadx.core.dex.visitors;
 
+import jadx.core.dex.attributes.AType;
 import jadx.core.dex.nodes.ClassNode;
 import jadx.core.dex.nodes.MethodNode;
 import jadx.core.utils.ErrorsCounter;
@@ -23,6 +24,9 @@ public class DepthTraversal {
 	}
 
 	public static void visit(IDexTreeVisitor visitor, MethodNode mth) {
+		if (mth.contains(AType.JADX_ERROR)) {
+			return;
+		}
 		try {
 			visitor.visit(mth);
 		} catch (Throwable e) {

jadx-core/src/test/java/jadx/tests/api/IntegrationTest.java

@@ -335,13 +335,15 @@ public abstract class IntegrationTest extends TestUtils {
 		return files;
 	}
 
-	public void noDebugInfo() {
+	protected void noDebugInfo() {
 		this.withDebugInfo = false;
 	}
 
-	// Try to make test class compilable
-	@Deprecated
-	public void disableCompilation() {
+	protected void setFallback() {
+		this.isFallback = true;
+	}
+
+	protected void disableCompilation() {
 		this.compile = false;
 	}
 
@@ -351,12 +353,6 @@ public abstract class IntegrationTest extends TestUtils {
 		this.outputCFG = true;
 	}
 
-	// Use only for debug purpose
-	@Deprecated
-	protected void setFallback() {
-		this.isFallback = true;
-	}
-
 	// Use only for debug purpose
 	@Deprecated
 	protected void notDeleteTmpJar() {

jadx-core/src/test/java/jadx/tests/api/SmaliTest.java

@@ -25,7 +25,7 @@ public class SmaliTest extends IntegrationTest {
 		return getClassNodeFromFile(outDex, fullClsName);
 	}
 
-	private File getSmaliFile(String clsName) {
+	private static File getSmaliFile(String clsName) {
 		File smaliFile = new File(SMALI_TESTS_DIR, clsName + SMALI_TESTS_EXT);
 		if (smaliFile.exists()) {
 			return smaliFile;
@@ -38,7 +38,7 @@ public class SmaliTest extends IntegrationTest {
 		return null;
 	}
 
-	public boolean compileSmali(File input, File output) {
+	private static boolean compileSmali(File input, File output) {
 		List<String> args = new ArrayList<String>();
 		args.add(input.getAbsolutePath());
 

jadx-core/src/test/java/jadx/tests/integration/fallback/TestFallbackMode.java

@@ -0,0 +1,37 @@
+package jadx.tests.integration.fallback;
+
+import jadx.core.dex.nodes.ClassNode;
+import jadx.tests.api.IntegrationTest;
+
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.CoreMatchers.not;
+import static org.junit.Assert.assertThat;
+
+public class TestFallbackMode extends IntegrationTest {
+
+	public static class TestCls {
+
+		public int test(int a) {
+			while (a < 10) {
+				a++;
+			}
+			return a;
+		}
+	}
+
+	@Test
+	public void test() {
+		setFallback();
+		disableCompilation();
+
+		ClassNode cls = getClassNode(TestCls.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, containsString("public int test(int r2) {"));
+		assertThat(code, containsString("r1_this = this;"));
+		assertThat(code, containsString("L_0x0004:"));
+		assertThat(code, not(containsString("throw new UnsupportedOperationException")));
+	}
+}