Optimize switch fallthrough

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

@@ -56,7 +56,7 @@ public List<BlockNode> prepareBlocks() {
 					if (!block.contains(AFlag.EXC_BOTTOM_SPLITTER)) {
 						startLabel.set(block.getId());
 					}
-					if (prev.getSuccessors().size() == 1 && !mth.isPreExitBlocks(prev)) {
+					if (prev.getSuccessors().size() == 1 && !mth.isPreExitBlock(prev)) {
 						endGoto.set(prev.getId());
 					}
 				}
@@ -68,7 +68,7 @@ public List<BlockNode> prepareBlocks() {
 			if (block.contains(AType.EXC_HANDLER)) {
 				startLabel.set(block.getId());
 			}
-			if (nextBlock == null && !mth.isPreExitBlocks(block)) {
+			if (nextBlock == null && !mth.isPreExitBlock(block)) {
 				endGoto.set(block.getId());
 			}
 			prev = block;
@@ -145,7 +145,7 @@ public boolean isNeedEndGoto(BlockNode block) {
 	// DFS sort blocks to reduce goto count
 	private List<BlockNode> getSortedBlocks() {
 		List<BlockNode> list = new ArrayList<>(mth.getBasicBlocks().size());
-		BlockUtils.dfsVisit(mth, list::add);
+		BlockUtils.visitDFS(mth, list::add);
 		return list;
 	}
 }

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

@@ -46,6 +46,11 @@ public final class BlockNode extends AttrNode implements IBlock, Comparable<Bloc
 	 */
 	private BitSet doms = EmptyBitSet.EMPTY;
 
+	/**
+	 * Post dominators, excluding self
+	 */
+	private BitSet postDoms = EmptyBitSet.EMPTY;
+
 	/**
 	 * Dominance frontier
 	 */
@@ -56,6 +61,11 @@ public final class BlockNode extends AttrNode implements IBlock, Comparable<Bloc
 	 */
 	private BlockNode idom;
 
+	/**
+	 * Immediate post dominator
+	 */
+	private BlockNode iPostDom;
+
 	/**
 	 * Blocks on which dominates this block
 	 */
@@ -165,6 +175,14 @@ public void setDoms(BitSet doms) {
 		this.doms = doms;
 	}
 
+	public BitSet getPostDoms() {
+		return postDoms;
+	}
+
+	public void setPostDoms(BitSet postDoms) {
+		this.postDoms = postDoms;
+	}
+
 	public BitSet getDomFrontier() {
 		return domFrontier;
 	}
@@ -184,6 +202,14 @@ public void setIDom(BlockNode idom) {
 		this.idom = idom;
 	}
 
+	public BlockNode getIPostDom() {
+		return iPostDom;
+	}
+
+	public void setIPostDom(BlockNode iPostDom) {
+		this.iPostDom = iPostDom;
+	}
+
 	public List<BlockNode> getDominatesOn() {
 		return dominatesOn;
 	}
@@ -233,6 +259,6 @@ public String baseString() {
 
 	@Override
 	public String toString() {
-		return "B:" + cid + ':' + InsnUtils.formatOffset(startOffset);
+		return "B:" + id + ':' + InsnUtils.formatOffset(startOffset);
 	}
 }

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

@@ -360,10 +360,13 @@ public List<BlockNode> getBasicBlocks() {
 
 	public void setBasicBlocks(List<BlockNode> blocks) {
 		this.blocks = blocks;
-		int i = 0;
-		for (BlockNode block : blocks) {
-			block.setId(i);
-			i++;
+		updateBlockIds(blocks);
+	}
+
+	public void updateBlockIds(List<BlockNode> blocks) {
+		int count = blocks.size();
+		for (int i = 0; i < count; i++) {
+			blocks.get(i).setId(i);
 		}
 	}
 
@@ -391,7 +394,7 @@ public List<BlockNode> getPreExitBlocks() {
 		return exitBlock.getPredecessors();
 	}
 
-	public boolean isPreExitBlocks(BlockNode block) {
+	public boolean isPreExitBlock(BlockNode block) {
 		List<BlockNode> successors = block.getSuccessors();
 		if (successors.size() == 1) {
 			return successors.get(0).equals(exitBlock);

jadx-core/src/main/java/jadx/core/dex/regions/SwitchRegion.java

@@ -15,7 +15,12 @@
 
 public final class SwitchRegion extends AbstractRegion implements IBranchRegion {
 
-	public static final Object DEFAULT_CASE_KEY = new Object();
+	public static final Object DEFAULT_CASE_KEY = new Object() {
+		@Override
+		public String toString() {
+			return "default";
+		}
+	};
 
 	private final BlockNode header;
 

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

@@ -199,7 +199,7 @@ private void processBlock(MethodNode mth, BlockNode block, boolean error) {
 				dot.add("color=red,");
 			}
 			dot.add("label=\"{");
-			dot.add(String.valueOf(block.getCId())).add("\\:\\ ");
+			dot.add(String.valueOf(block.getId())).add("\\:\\ ");
 			dot.add(InsnUtils.formatOffset(block.getStartOffset()));
 			if (!attrs.isEmpty()) {
 				dot.add('|').add(attrs);
@@ -208,6 +208,8 @@ private void processBlock(MethodNode mth, BlockNode block, boolean error) {
 				dot.add('|');
 				dot.startLine("doms: ").add(escape(block.getDoms()));
 				dot.startLine("\\lidom: ").add(escape(block.getIDom()));
+				dot.startLine("\\lpost-doms: ").add(escape(block.getPostDoms()));
+				dot.startLine("\\lpost-idom: ").add(escape(block.getIPostDom()));
 				dot.startLine("\\ldom-f: ").add(escape(block.getDomFrontier()));
 				dot.startLine("\\ldoms-on: ").add(escape(Utils.listToString(block.getDominatesOn())));
 				dot.startLine("\\l");
@@ -230,10 +232,10 @@ private void processBlock(MethodNode mth, BlockNode block, boolean error) {
 
 			if (PRINT_DOMINATORS) {
 				for (BlockNode c : block.getDominatesOn()) {
-					conn.startLine(block.getCId() + " -> " + c.getCId() + "[color=green];");
+					conn.startLine(block.getId() + " -> " + c.getId() + "[color=green];");
 				}
 				for (BlockNode dom : BlockUtils.bitSetToBlocks(mth, block.getDomFrontier())) {
-					conn.startLine("f_" + block.getCId() + " -> f_" + dom.getCId() + "[color=blue];");
+					conn.startLine("f_" + block.getId() + " -> f_" + dom.getId() + "[color=blue];");
 				}
 			}
 		}
@@ -273,7 +275,7 @@ private String attributesString(IAttributeNode block) {
 		private String makeName(IContainer c) {
 			String name;
 			if (c instanceof BlockNode) {
-				name = "Node_" + ((BlockNode) c).getCId();
+				name = "Node_" + ((BlockNode) c).getId();
 			} else if (c instanceof IBlock) {
 				name = "Node_" + c.getClass().getSimpleName() + '_' + c.hashCode();
 			} else {

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

@@ -68,7 +68,7 @@ public static boolean process(MethodNode mth) {
 		BlockProcessor.removeMarkedBlocks(mth);
 
 		BlockSet sorted = new BlockSet(mth);
-		BlockUtils.dfsVisit(mth, sorted::set);
+		BlockUtils.visitDFS(mth, sorted::set);
 		removeUnusedExcHandlers(mth, tryBlocks, sorted);
 		return true;
 	}

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

@@ -70,6 +70,8 @@ private static void processBlocksTree(MethodNode mth) {
 		registerLoops(mth);
 		processNestedLoops(mth);
 
+		PostDominatorTree.compute(mth);
+
 		updateCleanSuccessors(mth);
 		if (!mth.contains(AFlag.DISABLE_BLOCKS_LOCK)) {
 			mth.finishBasicBlocks();

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

@@ -3,8 +3,7 @@
 import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.List;
-
-import org.jetbrains.annotations.NotNull;
+import java.util.function.Function;
 
 import jadx.core.dex.nodes.BlockNode;
 import jadx.core.dex.nodes.MethodNode;
@@ -23,23 +22,22 @@ public class DominatorTree {
 
 	public static void compute(MethodNode mth) {
 		List<BlockNode> sorted = sortBlocks(mth);
-		BlockNode[] doms = build(sorted);
+		BlockNode[] doms = build(sorted, BlockNode::getPredecessors);
 		apply(sorted, doms);
 	}
 
 	private static List<BlockNode> sortBlocks(MethodNode mth) {
 		int blocksCount = mth.getBasicBlocks().size();
 		List<BlockNode> sorted = new ArrayList<>(blocksCount);
-		BlockUtils.dfsVisit(mth, sorted::add);
+		BlockUtils.visitDFS(mth, sorted::add);
 		if (sorted.size() != blocksCount) {
 			throw new JadxRuntimeException("Found unreachable blocks");
 		}
 		mth.setBasicBlocks(sorted);
 		return sorted;
 	}
 
-	@NotNull
-	private static BlockNode[] build(List<BlockNode> sorted) {
+	static BlockNode[] build(List<BlockNode> sorted, Function<BlockNode, List<BlockNode>> predFunc) {
 		int blocksCount = sorted.size();
 		BlockNode[] doms = new BlockNode[blocksCount];
 		doms[0] = sorted.get(0);
@@ -48,7 +46,7 @@ private static BlockNode[] build(List<BlockNode> sorted) {
 			changed = false;
 			for (int blockId = 1; blockId < blocksCount; blockId++) {
 				BlockNode b = sorted.get(blockId);
-				List<BlockNode> preds = b.getPredecessors();
+				List<BlockNode> preds = predFunc.apply(b);
 				int pickedPred = -1;
 				BlockNode newIDom = null;
 				for (BlockNode pred : preds) {
@@ -60,7 +58,7 @@ private static BlockNode[] build(List<BlockNode> sorted) {
 					}
 				}
 				if (newIDom == null) {
-					throw new JadxRuntimeException("No predecessors for block: " + b);
+					throw new JadxRuntimeException("No immediate dominator for block: " + b);
 				}
 				for (BlockNode predBlock : preds) {
 					int predId = predBlock.getId();
@@ -110,7 +108,7 @@ private static void apply(List<BlockNode> sorted, BlockNode[] doms) {
 		}
 	}
 
-	private static BitSet collectDoms(BlockNode[] doms, BlockNode idom) {
+	static BitSet collectDoms(BlockNode[] doms, BlockNode idom) {
 		BitSet domBS = new BitSet(doms.length);
 		BlockNode nextIDom = idom;
 		while (true) {

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

@@ -0,0 +1,65 @@
+package jadx.core.dex.visitors.blocks;
+
+import java.util.ArrayList;
+import java.util.BitSet;
+import java.util.List;
+
+import jadx.core.dex.nodes.BlockNode;
+import jadx.core.dex.nodes.MethodNode;
+import jadx.core.utils.BlockUtils;
+import jadx.core.utils.EmptyBitSet;
+
+public class PostDominatorTree {
+
+	public static void compute(MethodNode mth) {
+		try {
+			int mthBlocksCount = mth.getBasicBlocks().size();
+			List<BlockNode> sorted = new ArrayList<>(mthBlocksCount);
+			BlockUtils.visitReverseDFS(mth, sorted::add);
+			// temporary set block ids to match reverse sorted order
+			// save old ids for later remapping
+			int blocksCount = sorted.size();
+			int[] ids = new int[mthBlocksCount];
+			for (int i = 0; i < blocksCount; i++) {
+				ids[i] = sorted.get(i).getId();
+			}
+			mth.updateBlockIds(sorted);
+
+			BlockNode[] postDoms = DominatorTree.build(sorted, BlockNode::getSuccessors);
+			BlockNode firstBlock = sorted.get(0);
+			firstBlock.setPostDoms(EmptyBitSet.EMPTY);
+			firstBlock.setIPostDom(null);
+			for (int i = 1; i < blocksCount; i++) {
+				BlockNode block = sorted.get(i);
+				BlockNode iPostDom = postDoms[i];
+				block.setIPostDom(iPostDom);
+				BitSet postDomBS = DominatorTree.collectDoms(postDoms, iPostDom);
+				block.setPostDoms(postDomBS);
+			}
+			for (int i = 1; i < blocksCount; i++) {
+				BlockNode block = sorted.get(i);
+				BitSet bs = new BitSet(blocksCount);
+				block.getPostDoms().stream().forEach(n -> bs.set(ids[n]));
+				bs.clear(ids[i]);
+				block.setPostDoms(bs);
+			}
+			// check for missing blocks in 'sorted' list
+			// can be caused by infinite loops
+			int blocksDelta = mthBlocksCount - blocksCount;
+			if (blocksDelta != 0) {
+				int insnsCount = 0;
+				for (BlockNode block : mth.getBasicBlocks()) {
+					if (block.getPostDoms() == null) {
+						block.setPostDoms(EmptyBitSet.EMPTY);
+						block.setIPostDom(null);
+						insnsCount += block.getInstructions().size();
+					}
+				}
+				mth.addInfoComment("Infinite loop detected, blocks: " + blocksDelta + ", insns: " + insnsCount);
+			}
+		} finally {
+			// revert block ids change
+			mth.updateBlockIds(mth.getBasicBlocks());
+		}
+	}
+}