Re-enable simpleMerge with additional scoping restrictions

I've changed it to only merge variables within the same basic block,
which improves the output significantly.

src/org/jetbrains/java/decompiler/modules/decompiler/vars/VarVersionsProcessor.java

@@ -4,10 +4,12 @@ package org.jetbrains.java.decompiler.modules.decompiler.vars;
 import org.jetbrains.java.decompiler.code.CodeConstants;
 import org.jetbrains.java.decompiler.main.DecompilerContext;
 import org.jetbrains.java.decompiler.main.collectors.CounterContainer;
+import org.jetbrains.java.decompiler.modules.decompiler.exps.AssignmentExprent;
 import org.jetbrains.java.decompiler.modules.decompiler.exps.ConstExprent;
 import org.jetbrains.java.decompiler.modules.decompiler.exps.Exprent;
 import org.jetbrains.java.decompiler.modules.decompiler.exps.VarExprent;
 import org.jetbrains.java.decompiler.modules.decompiler.sforms.DirectGraph;
+import org.jetbrains.java.decompiler.modules.decompiler.sforms.DirectNode;
 import org.jetbrains.java.decompiler.modules.decompiler.sforms.FlattenStatementsHelper;
 import org.jetbrains.java.decompiler.modules.decompiler.sforms.SSAConstructorSparseEx;
 import org.jetbrains.java.decompiler.modules.decompiler.stats.RootStatement;
@@ -40,7 +42,7 @@ public class VarVersionsProcessor {
 
     typeProcessor.calculateVarTypes(root, graph);
 
-    //simpleMerge(typeProcessor, graph, method);
+    simpleMerge(typeProcessor, graph, method);
 
     // FIXME: advanced merging
 
@@ -166,6 +168,39 @@ public class VarVersionsProcessor {
 
           for (int j = i + 1; j < lstVersions.size(); j++) {
             VarVersionPair secondPair = new VarVersionPair(ent.getKey(), lstVersions.get(j));
+
+            // find all scopes the two variable versions are assigned in
+            Set<DirectNode> nodes = new HashSet<>();
+            for (DirectNode node : graph.nodes) {
+              for (Exprent expr : node.exprents) {
+                if (expr.type != Exprent.EXPRENT_ASSIGNMENT) {
+                  continue;
+                }
+
+                AssignmentExprent assignExpr = (AssignmentExprent) expr;
+
+                Exprent leftExpr = assignExpr.getLeft();
+                if (leftExpr.type != Exprent.EXPRENT_VAR) {
+                  continue;
+                }
+
+                VarExprent varExpr = (VarExprent) leftExpr;
+                int index = varExpr.getIndex();
+                int version = varExpr.getVersion();
+
+                if (index == firstPair.var && version == firstPair.version) {
+                  nodes.add(node);
+                } else if (index == secondPair.var && version == secondPair.version) {
+                  nodes.add(node);
+                }
+              }
+            }
+
+            // only merge variables if they're assigned in the same scope
+            if (nodes.size() > 1) {
+              continue;
+            }
+
             VarType secondType = mapExprentMinTypes.get(secondPair);
 
             if (firstType.equals(secondType) ||