fix: field increment (PR #550)

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

@@ -49,12 +49,36 @@ public class SimplifyVisitor extends AbstractVisitor {
 			for (int i = 0; i < list.size(); i++) {
 				InsnNode modInsn = simplifyInsn(mth, list.get(i));
 				if (modInsn != null) {
+					if (i != 0 && modInsn.contains(AFlag.ARITH_ONEARG)) {
+
+						InsnNode mergedNode = simplifyOneArgConsecutive(
+								list.get(i - 1), list.get(i), (ArithNode) modInsn);
+
+						if (mergedNode != null) {
+							list.remove(i - 1);
+							modInsn = mergedNode;
+							i--;
+						}
+					}
 					list.set(i, modInsn);
 				}
 			}
 		}
 	}
 
+	private static InsnNode simplifyOneArgConsecutive(InsnNode insn1, InsnNode insn2, ArithNode modInsn) {
+		if (insn1.getType() == InsnType.IGET
+				&& insn2.getType() == InsnType.IPUT
+				&& insn1.getResult().getSVar().getUseCount() == 2
+				&& insn2.getArg(1).equals(insn1.getResult())) {
+
+			FieldInfo field = (FieldInfo) ((IndexInsnNode) insn2).getIndex();
+			FieldArg fArg = new FieldArg(field, new InsnWrapArg(insn1));
+			return new ArithNode(modInsn.getOp(), fArg, modInsn.getArg(1));
+		}
+		return null;
+	}
+
 	private static InsnNode simplifyInsn(MethodNode mth, InsnNode insn) {
 		if (insn.contains(AFlag.DONT_GENERATE)) {
 			return null;

jadx-core/src/test/java/jadx/tests/integration/arith/TestFieldIncrement2.java

@@ -2,7 +2,6 @@ package jadx.tests.integration.arith;
 
 import org.junit.jupiter.api.Test;
 
-import jadx.NotYetImplemented;
 import jadx.core.dex.nodes.ClassNode;
 import jadx.tests.api.IntegrationTest;
 
@@ -33,15 +32,6 @@ public class TestFieldIncrement2 extends IntegrationTest {
 		String code = cls.getCode().toString();
 
 		assertThat(code, containsString("this.a.f += n;"));
-		assertThat(code, containsString("a2.f *= n;"));
-	}
-
-	@Test
-	@NotYetImplemented
-	public void test2() {
-		ClassNode cls = getClassNode(TestCls.class);
-		String code = cls.getCode().toString();
-
 		assertThat(code, containsString("this.a.f *= n;"));
 	}
 }