fix: support end block entry for mutli-entry loops (#889)

jadx-core/src/main/java/jadx/core/dex/visitors/blocks/FixMultiEntryLoops.java

@@ -22,8 +22,7 @@ public static boolean process(MethodNode mth) {
 		}
 		List<SpecialEdgeAttr> specialEdges = mth.getAll(AType.SPECIAL_EDGE);
 		List<SpecialEdgeAttr> multiEntryLoops = specialEdges.stream()
-				.filter(e -> e.getType() == SpecialEdgeType.BACK_EDGE)
-				.filter(e -> !isSingleEntryLoop(e))
+				.filter(e -> e.getType() == SpecialEdgeType.BACK_EDGE && !isSingleEntryLoop(e))
 				.collect(Collectors.toList());
 		if (multiEntryLoops.isEmpty()) {
 			return false;
@@ -42,25 +41,50 @@ public static boolean process(MethodNode mth) {
 	}
 
 	private static boolean fixLoop(MethodNode mth, SpecialEdgeAttr backEdge, List<SpecialEdgeAttr> crossEdges) {
+		if (isHeaderSuccessorEntry(mth, backEdge, crossEdges)) {
+			return true;
+		}
+		if (isEndBlockEntry(mth, backEdge, crossEdges)) {
+			return true;
+		}
+		mth.addWarnComment("Unsupported multi-entry loop pattern (" + backEdge + "). Please report as a decompilation issue!!!");
+		return false;
+	}
+
+	private static boolean isHeaderSuccessorEntry(MethodNode mth, SpecialEdgeAttr backEdge, List<SpecialEdgeAttr> crossEdges) {
 		BlockNode header = backEdge.getEnd();
 		BlockNode headerIDom = header.getIDom();
 		SpecialEdgeAttr subEntry = ListUtils.filterOnlyOne(crossEdges, e -> e.getStart() == headerIDom);
-		if (subEntry == null || !isSupportedPattern(header, subEntry)) {
-			// TODO: for now only sub entry in header successor is supported
-			mth.addWarnComment("Unsupported multi-entry loop pattern (" + backEdge + "). Please submit an issue!!!");
+		if (subEntry == null || !ListUtils.isSingleElement(header.getSuccessors(), subEntry.getEnd())) {
 			return false;
 		}
 		BlockNode loopEnd = backEdge.getStart();
 		BlockNode subEntryBlock = subEntry.getEnd();
 		BlockNode copyHeader = BlockSplitter.insertBlockBetween(mth, loopEnd, header);
 		BlockSplitter.copyBlockData(header, copyHeader);
 		BlockSplitter.replaceConnection(copyHeader, header, subEntryBlock);
-		mth.addDebugComment("Duplicate block to fix multi-entry loop: " + backEdge);
+		mth.addDebugComment("Duplicate block (" + header + ") to fix multi-entry loop: " + backEdge);
+		return true;
+	}
+
+	private static boolean isEndBlockEntry(MethodNode mth, SpecialEdgeAttr backEdge, List<SpecialEdgeAttr> crossEdges) {
+		BlockNode loopEnd = backEdge.getStart();
+		SpecialEdgeAttr subEntry = ListUtils.filterOnlyOne(crossEdges, e -> e.getEnd() == loopEnd);
+		if (subEntry == null) {
+			return false;
+		}
+		dupPath(mth, subEntry.getStart(), loopEnd, backEdge.getEnd());
+		mth.addDebugComment("Duplicate block (" + loopEnd + ") to fix multi-entry loop: " + backEdge);
 		return true;
 	}
 
-	private static boolean isSupportedPattern(BlockNode header, SpecialEdgeAttr subEntry) {
-		return ListUtils.isSingleElement(header.getSuccessors(), subEntry.getEnd());
+	/**
+	 * Duplicate 'center' block on path from 'start' to 'end'
+	 */
+	private static void dupPath(MethodNode mth, BlockNode start, BlockNode center, BlockNode end) {
+		BlockNode copyCenter = BlockSplitter.insertBlockBetween(mth, start, end);
+		BlockSplitter.copyBlockData(center, copyCenter);
+		BlockSplitter.removeConnection(start, center);
 	}
 
 	private static boolean isSingleEntryLoop(SpecialEdgeAttr e) {
@@ -75,21 +99,18 @@ private enum BlockColor {
 	}
 
 	private static void detectSpecialEdges(MethodNode mth) {
-		List<BlockNode> blocks = mth.getBasicBlocks();
-		BlockColor[] colors = new BlockColor[blocks.size()];
+		BlockColor[] colors = new BlockColor[mth.getBasicBlocks().size()];
 		Arrays.fill(colors, BlockColor.WHITE);
-		colorDFS(mth, blocks, colors, mth.getEnterBlock().getId());
+		colorDFS(mth, colors, mth.getEnterBlock());
 	}
 
 	// TODO: transform to non-recursive form
-	private static void colorDFS(MethodNode mth, List<BlockNode> blocks, BlockColor[] colors, int cur) {
-		colors[cur] = BlockColor.GRAY;
-		BlockNode block = blocks.get(cur);
+	private static void colorDFS(MethodNode mth, BlockColor[] colors, BlockNode block) {
+		colors[block.getId()] = BlockColor.GRAY;
 		for (BlockNode v : block.getSuccessors()) {
-			int vId = v.getId();
-			switch (colors[vId]) {
+			switch (colors[v.getId()]) {
 				case WHITE:
-					colorDFS(mth, blocks, colors, vId);
+					colorDFS(mth, colors, v);
 					break;
 				case GRAY:
 					mth.addAttr(AType.SPECIAL_EDGE, new SpecialEdgeAttr(SpecialEdgeType.BACK_EDGE, block, v));
@@ -99,6 +120,6 @@ private static void colorDFS(MethodNode mth, List<BlockNode> blocks, BlockColor[
 					break;
 			}
 		}
-		colors[cur] = BlockColor.BLACK;
+		colors[block.getId()] = BlockColor.BLACK;
 	}
 }

jadx-core/src/test/java/jadx/tests/integration/loops/TestMultiEntryLoop2.java

@@ -0,0 +1,17 @@
+package jadx.tests.integration.loops;
+
+import org.junit.jupiter.api.Test;
+
+import jadx.tests.api.SmaliTest;
+
+import static jadx.tests.api.utils.assertj.JadxAssertions.assertThat;
+
+public class TestMultiEntryLoop2 extends SmaliTest {
+
+	@Test
+	public void test() {
+		assertThat(getClassNodeFromSmali())
+				.code()
+				.containsOne("while (true) {");
+	}
+}

jadx-core/src/test/smali/loops/TestMultiEntryLoop2.smali

@@ -0,0 +1,92 @@
+.class public Lloops/TestMultiEntryLoop2;
+.super Ljava/lang/Object;
+
+.field public list:Ljava/util/List;
+    .annotation system Ldalvik/annotation/Signature;
+        value = {
+            "Ljava/util/List<",
+            "Ljava/lang/String;",
+            ">;"
+        }
+    .end annotation
+.end field
+
+.method private test(Ljava/lang/String;II)V
+    .registers 14
+
+    if-ne p2, p3, :cond_3
+    return-void
+
+    :cond_3
+    invoke-virtual {p1, p2}, Ljava/lang/String;->charAt(I)C
+
+    move-result v0
+    const/16 v1, 0x2f
+    const-string v2, ""
+    const/4 v3, 0x1
+
+    if-eq v0, v1, :cond_1e
+    const/16 v1, 0x5c
+    if-ne v0, v1, :cond_13
+
+    goto :goto_1e
+
+    :cond_13
+    iget-object v0, p0, Lloops/TestMultiEntryLoop2;->list:Ljava/util/List;
+    invoke-interface {v0}, Ljava/util/List;->size()I
+    move-result v1
+    sub-int/2addr v1, v3
+    invoke-interface {v0, v1, v2}, Ljava/util/List;->set(ILjava/lang/Object;)Ljava/lang/Object;
+    goto :goto_29
+
+    :cond_1e
+    :goto_1e
+    iget-object v0, p0, Lloops/TestMultiEntryLoop2;->list:Ljava/util/List;
+    invoke-interface {v0}, Ljava/util/List;->clear()V
+    .line 4
+    iget-object v0, p0, Lloops/TestMultiEntryLoop2;->list:Ljava/util/List;
+    invoke-interface {v0, v2}, Ljava/util/List;->add(Ljava/lang/Object;)Z
+    goto :goto_41
+
+    :cond_29
+    :goto_29
+    move v6, p2
+    if-ge v6, p3, :cond_44
+    const-string p2, "/\\"
+    .line 5
+    invoke-static {p1, v6, p3, p2}, Lloops/TestMultiEntryLoop2;->delimiterOffset(Ljava/lang/String;IILjava/lang/String;)I
+    move-result p2
+    if-ge p2, p3, :cond_36
+    move v0, v3
+    goto :goto_37
+
+    :cond_36
+    const/4 v0, 0x0
+    :goto_37
+    const/4 v9, 0x1
+    move-object v4, p0
+    move-object v5, p1
+    move v7, p2
+    move v8, v0
+    .line 6
+    invoke-direct/range {v4 .. v9}, Lloops/TestMultiEntryLoop2;->push(Ljava/lang/String;IIZZ)V
+    if-eqz v0, :cond_29
+
+    :goto_41
+    add-int/lit8 p2, p2, 0x1
+    goto :goto_29
+
+    :cond_44
+    return-void
+.end method
+
+.method private push(Ljava/lang/String;IIZZ)V
+    .locals 0
+    return-void
+.end method
+
+.method private delimiterOffset(Ljava/lang/String;IILjava/lang/String;)I
+    .locals 1
+    const/4 v0, 0x0
+    return v0
+.end method