Fix incorrect ppmm inlining (#451)

* Add bad test for ppmm inlining

* Update test

* Fix ppmm bug

* More bad case :(

* Fix array assign ppmm bug

Author: Kroppeb

src/org/jetbrains/java/decompiler/modules/decompiler/SimplifyExprentsHelper.java

@@ -683,20 +683,30 @@ private static boolean inlinePPIAndMMI(Exprent expr, Exprent next) {
   // Try to find the first valid usage of a variable for PPMM inlining.
   // Returns Pair{parent exprent, variable exprent to replace}
   private static Pair<Exprent, VarExprent> findFirstValidUsage(VarExprent match, Exprent next) {
-    Deque<Exprent> stack = new LinkedList<>();
+    List<Exprent> stack = new ArrayList<>();
+    List<Exprent> parent = new ArrayList<>();
     stack.add(next);
+    parent.add(null);
 
     while (!stack.isEmpty()) {
-      Exprent expr = stack.removeLast();
+      Exprent expr = stack.remove(stack.size() - 1);
+      Exprent parentExpr = parent.remove(parent.size() - 1);
 
       List<Exprent> exprents = expr.getAllExprents();
 
+      if (parentExpr != null &&
+        expr instanceof VarExprent ve &&
+        ve.getIndex() == match.getIndex() &&
+        ve.getVersion() == match.getVersion()) {
+        return Pair.of(parentExpr, ve);
+      }
+
       if (expr instanceof FunctionExprent) {
         FunctionExprent func = (FunctionExprent) expr;
 
         // Don't inline ppmm into more ppmm
         if (isPPMM(func)) {
-          continue;
+          return null;
         }
 
         // Don't consider || or &&
@@ -718,30 +728,18 @@ private static Pair<Exprent, VarExprent> findFirstValidUsage(VarExprent match, E
       // Reverse iteration to ensure DFS
       for (int i = exprents.size() - 1; i >= 0; i--) {
         Exprent ex = exprents.get(i);
-        boolean add = true;
-
-        // Skip LHS of assignment as it is invalid
-        if (expr instanceof AssignmentExprent) {
-          add = ex != ((AssignmentExprent) expr).getLeft();
-        }
 
-        // Check var if we find
-        if (add && ex instanceof VarExprent) {
-          VarExprent ve = (VarExprent) ex;
-
-          if (ve.getIndex() == match.getIndex() && ve.getVersion() == match.getVersion()) {
-            return Pair.of(expr, ve);
-          }
-        }
-
-        // Ignore ++/-- exprents as they aren't valid usages to replace
-        if (ex instanceof FunctionExprent) {
-          add = !isPPMM((FunctionExprent) ex);
+        // Avoid making something like `++a = 5`. It shouldn't happen but better be safe than sorry.
+        if (expr instanceof AssignmentExprent asExpr &&
+          ex == asExpr.getLeft() &&
+          ex instanceof VarExprent innerEx &&
+          innerEx.getIndex() == match.getIndex()
+        ) {
+          continue;
         }
 
-        if (add) {
-          stack.add(ex);
-        }
+        stack.add(ex);
+        parent.add(expr);
       }
     }
 

testData/results/pkg/TestArrayPPMM.dec

@@ -37,8 +37,20 @@ public class TestArrayPPMM {
       this.accept(array[i++], array[++i]);// 39
    }// 40
 
-   private void accept(int i, int j) {
+   public void test9(int[] array, int i) {
+      array[++i] = i;// 43
    }// 44
+
+   public void test10(int i) {
+      this.getArray()[++i] = i;// 47
+   }// 48
+
+   private void accept(int i, int j) {
+   }// 52
+
+   private int[] getArray() {
+      return new int[10];// 55
+   }
 }
 
 class 'pkg/TestArrayPPMM' {
@@ -190,8 +202,37 @@ class 'pkg/TestArrayPPMM' {
       10      37
    }
 
-   method 'accept (II)V' {
+   method 'test9 ([II)V' {
       0      40
+      1      40
+      2      40
+      3      40
+      5      40
+      6      40
+      7      41
+   }
+
+   method 'test10 (I)V' {
+      0      44
+      1      44
+      2      44
+      3      44
+      4      44
+      5      44
+      6      44
+      8      44
+      9      44
+      a      45
+   }
+
+   method 'accept (II)V' {
+      0      48
+   }
+
+   method 'getArray ()[I' {
+      0      51
+      1      51
+      4      51
    }
 }
 
@@ -214,4 +255,9 @@ Lines mapping:
 36 <-> 34
 39 <-> 37
 40 <-> 38
-44 <-> 41
+43 <-> 41
+44 <-> 42
+47 <-> 45
+48 <-> 46
+52 <-> 49
+55 <-> 52