core: fix type for one time used args

jadx-core/src/main/java/jadx/core/dex/instructions/InsnDecoder.java

@@ -473,7 +473,7 @@ public class InsnDecoder {
 			case Opcodes.ARRAY_LENGTH: {
 				InsnNode node = new InsnNode(InsnType.ARRAY_LENGTH, 1);
 				node.setResult(InsnArg.reg(insn, 0, ArgType.INT));
-				node.addArg(InsnArg.reg(insn, 1, ArgType.unknown(PrimitiveType.ARRAY)));
+				node.addArg(InsnArg.reg(insn, 1, ArgType.array(ArgType.UNKNOWN)));
 				return node;
 			}
 

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

@@ -54,7 +54,6 @@ public class ConstInlinerVisitor extends AbstractVisitor {
 
 	private static boolean replaceConst(MethodNode mth, BlockNode block, InsnNode insn, long literal) {
 		List<InsnArg> use = insn.getResult().getTypedVar().getUseList();
-
 		int replace = 0;
 		for (InsnArg arg : use) {
 			InsnNode useInsn = arg.getParentInsn();
@@ -64,9 +63,15 @@ public class ConstInlinerVisitor extends AbstractVisitor {
 			BlockNode useBlock = BlockUtils.getBlockByInsn(mth, useInsn);
 			if (useBlock == block || useBlock.isDominator(block)) {
 				if (arg != insn.getResult() && !registerReassignOnPath(block, useBlock, insn)) {
-					// in most cases type not equal arg.getType()
-					// just set unknown type and run type fixer
-					LiteralArg litArg = InsnArg.lit(literal, ArgType.UNKNOWN);
+					LiteralArg litArg;
+					if (use.size() == 2) {
+						// arg used only in one place
+						litArg = InsnArg.lit(literal, arg.getType());
+					} else {
+						// in most cases type not equal arg.getType()
+						// just set unknown type and run type fixer
+						litArg = InsnArg.lit(literal, ArgType.UNKNOWN);
+					}
 					if (useInsn.replaceArg(arg, litArg)) {
 						fixTypes(mth, useInsn, litArg);
 						replace++;

jadx-core/src/test/java/jadx/tests/internal/TestWrongCode.java

@@ -0,0 +1,29 @@
+package jadx.tests.internal;
+
+import jadx.api.InternalJadxTest;
+import jadx.core.dex.nodes.ClassNode;
+
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.hamcrest.CoreMatchers.not;
+import static org.junit.Assert.assertThat;
+
+public class TestWrongCode extends InternalJadxTest {
+
+	public static class TestCls {
+		private int f() {
+			int[] a = null;
+			return a.length;
+		}
+	}
+
+	@Test
+	public void test() {
+		ClassNode cls = getClassNode(TestCls.class);
+		String code = cls.getCode().toString();
+
+		assertThat(code, not(containsString("return false.length;")));
+		assertThat(code, containsString("return null.length;"));
+	}
+}