fix: transform loop to for with branching at end

Signed-off-by: Skylot <skylot@gmail.com>

jadx-core/src/main/java/jadx/core/dex/attributes/AFlag.java

@@ -73,4 +73,6 @@ public enum AFlag {
 	SOFT_CAST, // synthetic cast to help type inference
 
 	INCONSISTENT_CODE, // warning about incorrect decompilation
+
+	REQUEST_IF_REGION_OPTIMIZE, // run if region visitor again
 }

jadx-core/src/main/java/jadx/core/dex/visitors/regions/IfRegionVisitor.java

@@ -26,7 +26,10 @@ public class IfRegionVisitor extends AbstractVisitor {
 		if (mth.isNoCode()) {
 			return;
 		}
+		process(mth);
+	}
 
+	public static void process(MethodNode mth) {
 		DepthRegionTraversal.traverseIterative(mth, TERNARY_VISITOR);
 		DepthRegionTraversal.traverse(mth, PROCESS_IF_REGION_VISITOR);
 		DepthRegionTraversal.traverseIterative(mth, REMOVE_REDUNDANT_ELSE_VISITOR);

jadx-core/src/main/java/jadx/core/dex/visitors/regions/LoopRegionVisitor.java

@@ -53,35 +53,43 @@ public class LoopRegionVisitor extends AbstractVisitor implements IRegionVisitor
 	@Override
 	public void visit(MethodNode mth) {
 		DepthRegionTraversal.traverse(mth, this);
+		if (mth.contains(AFlag.REQUEST_IF_REGION_OPTIMIZE)) {
+			IfRegionVisitor.process(mth);
+			mth.remove(AFlag.REQUEST_IF_REGION_OPTIMIZE);
+		}
 	}
 
 	@Override
 	public boolean enterRegion(MethodNode mth, IRegion region) {
 		if (region instanceof LoopRegion) {
-			processLoopRegion(mth, (LoopRegion) region);
+			if (processLoopRegion(mth, (LoopRegion) region)) {
+				// optimize `if` block after instructions remove
+				mth.add(AFlag.REQUEST_IF_REGION_OPTIMIZE);
+			}
 		}
 		return true;
 	}
 
-	private static void processLoopRegion(MethodNode mth, LoopRegion loopRegion) {
+	private static boolean processLoopRegion(MethodNode mth, LoopRegion loopRegion) {
 		if (loopRegion.isConditionAtEnd()) {
-			return;
+			return false;
 		}
 		IfCondition condition = loopRegion.getCondition();
 		if (condition == null) {
-			return;
+			return false;
 		}
 		if (checkForIndexedLoop(mth, loopRegion, condition)) {
-			return;
+			return true;
 		}
-		checkIterableForEach(mth, loopRegion, condition);
+		return checkIterableForEach(mth, loopRegion, condition);
 	}
 
 	/**
 	 * Check for indexed loop.
 	 */
 	private static boolean checkForIndexedLoop(MethodNode mth, LoopRegion loopRegion, IfCondition condition) {
-		InsnNode incrInsn = RegionUtils.getLastInsn(loopRegion);
+		BlockNode loopEndBlock = loopRegion.getInfo().getEnd();
+		InsnNode incrInsn = BlockUtils.getLastInsn(BlockUtils.skipSyntheticPredecessor(loopEndBlock));
 		if (incrInsn == null) {
 			return false;
 		}

jadx-core/src/test/java/jadx/tests/integration/loops/TestArrayForEach3.java

@@ -0,0 +1,44 @@
+package jadx.tests.integration.loops;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.tests.api.IntegrationTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+/**
+ * Issue #977
+ */
+public class TestArrayForEach3 extends IntegrationTest {
+
+	public static class TestCls {
+		public void test(String[] arr) {
+			for (String s : arr) {
+				if (s.length() > 0) {
+					return;
+				}
+			}
+			throw new IllegalArgumentException("All strings are empty");
+		}
+
+		public void check() {
+			test(new String[] { "", "a" }); // no exception
+			try {
+				test(new String[] { "", "" });
+				fail("IllegalArgumentException expected");
+			} catch (IllegalArgumentException e) {
+				// expected
+			}
+		}
+	}
+
+	@Test
+	public void test() {
+		noDebugInfo();
+		assertThat(getClassNode(TestCls.class))
+				.code()
+				.doesNotContain("while")
+				.containsOne("for (String str : strArr) {");
+	}
+}