Better fix for https://github.com/konsoletyper/teavm/issues/85

teavm-core/src/main/java/org/teavm/javascript/Optimizer.java

@@ -29,7 +29,13 @@ public class Optimizer {
     public void optimize(RegularMethodNode method, Program program) {
         ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
         stats.analyze(program);
-        OptimizingVisitor optimizer = new OptimizingVisitor(stats);
+        boolean[] preservedVars = new boolean[stats.writes.length];
+        for (int i = 0; i < preservedVars.length; ++i) {
+            if (stats.writes[i] != 1) {
+                preservedVars[i] = true;
+            }
+        }
+        OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.reads);
         method.getBody().acceptVisitor(optimizer);
         method.setBody(optimizer.resultStmt);
         int paramCount = method.getReference().parameterCount();
@@ -44,12 +50,21 @@ public class Optimizer {
     }
 
     public void optimize(AsyncMethodNode method, AsyncProgramSplitter splitter) {
-        ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
+        boolean[] preservedVars = new boolean[method.getVariables().size()];
+        int[][] readFrequencies = new int[splitter.size()][];
         for (int i = 0; i < splitter.size(); ++i) {
+            ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
             stats.analyze(splitter.getProgram(i));
+            readFrequencies[i] = stats.reads;
+            for (int j = 0; j < stats.writes.length; ++j) {
+                if (stats.readUninitialized[j] || stats.writes[j] != 1 && stats.reads[j] > 0) {
+                    preservedVars[j] = true;
+                }
+            }
         }
-        for (AsyncMethodPart part : method.getBody()) {
+        for (int i = 0; i < splitter.size(); ++i) {
-            OptimizingVisitor optimizer = new OptimizingVisitor(stats.copy());
+            AsyncMethodPart part = method.getBody().get(i);
+            OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, readFrequencies[i]);
             part.getStatement().acceptVisitor(optimizer);
             part.setStatement(optimizer.resultStmt);
         }

teavm-core/src/main/java/org/teavm/javascript/OptimizingVisitor.java

@@ -25,11 +25,13 @@ import org.teavm.javascript.ast.*;
 class OptimizingVisitor implements StatementVisitor, ExprVisitor {
     public Expr resultExpr;
     public Statement resultStmt;
-    private ReadWriteStatsBuilder stats;
+    private boolean[] preservedVars;
+    private int[] readFrequencies;
     private List<Statement> resultSequence;
 
-    public OptimizingVisitor(ReadWriteStatsBuilder stats) {
+    public OptimizingVisitor(boolean[] preservedVars, int[] readFreqencies) {
-        this.stats = stats;
+        this.preservedVars = preservedVars;
+        this.readFrequencies = readFreqencies;
     }
 
     private static boolean isZero(Expr expr) {
@@ -121,7 +123,7 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
     public void visit(VariableExpr expr) {
         int index = expr.getIndex();
         resultExpr = expr;
-        if (stats.reads[index] != 1 || stats.writes[index] != 1) {
+        if (readFrequencies[index] != 1 || preservedVars[index]) {
             return;
         }
         if (resultSequence.isEmpty()) {
@@ -217,7 +219,7 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
         InvocationExpr constructrExpr = Expr.constructObject(expr.getMethod(), args);
         constructrExpr.setLocation(expr.getLocation());
         assignment.setRightValue(constructrExpr);
-        stats.reads[var.getIndex()]--;
+        readFrequencies[var.getIndex()]--;
         return true;
     }
 

teavm-core/src/main/java/org/teavm/javascript/ReadWriteStatsBuilder.java

@@ -16,8 +16,12 @@
 package org.teavm.javascript;
 
 import java.util.Arrays;
+import org.teavm.common.Graph;
+import org.teavm.common.GraphUtils;
+import org.teavm.common.IntegerStack;
 import org.teavm.model.*;
 import org.teavm.model.util.DefinitionExtractor;
+import org.teavm.model.util.ProgramUtils;
 import org.teavm.model.util.UsageExtractor;
 
 /**
@@ -27,6 +31,7 @@ import org.teavm.model.util.UsageExtractor;
 class ReadWriteStatsBuilder {
     public int[] reads;
     public int[] writes;
+    public boolean[] readUninitialized;
 
     private ReadWriteStatsBuilder() {
     }
@@ -34,6 +39,7 @@ class ReadWriteStatsBuilder {
     public ReadWriteStatsBuilder(int variableCount) {
         reads = new int[variableCount];
         writes = new int[variableCount];
+        readUninitialized = new boolean[variableCount];
     }
 
     public ReadWriteStatsBuilder copy() {
@@ -44,10 +50,15 @@ class ReadWriteStatsBuilder {
     }
 
     public void analyze(Program program) {
+        Graph cfg = ProgramUtils.buildControlFlowGraph(program);
+        Graph dom = GraphUtils.buildDominatorGraph(GraphUtils.buildDominatorTree(cfg), cfg.size());
         DefinitionExtractor defExtractor = new DefinitionExtractor();
         UsageExtractor useExtractor = new UsageExtractor();
-        for (int i = 0; i < program.basicBlockCount(); ++i) {
+        IntegerStack stack = new IntegerStack(program.basicBlockCount());
-            BasicBlock block = program.basicBlockAt(i);
+        stack.push(0);
+        while (!stack.isEmpty()) {
+            int node = stack.pop();
+            BasicBlock block = program.basicBlockAt(node);
             for (Instruction insn : block.getInstructions()) {
                 insn.acceptVisitor(defExtractor);
                 insn.acceptVisitor(useExtractor);
@@ -56,18 +67,27 @@ class ReadWriteStatsBuilder {
                 }
                 for (Variable var : useExtractor.getUsedVariables()) {
                     reads[var.getIndex()]++;
+                    if (writes[var.getIndex()] == 0) {
+                        readUninitialized[var.getIndex()] = true;
+                    }
                 }
             }
             for (Phi phi : block.getPhis()) {
                 writes[phi.getReceiver().getIndex()] += phi.getIncomings().size();
                 for (Incoming incoming : phi.getIncomings()) {
-                    reads[incoming.getValue().getIndex()]++;
+                    if (writes[incoming.getValue().getIndex()] == 0) {
+                        reads[incoming.getValue().getIndex()]++;
+                    }
                 }
             }
             for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
                 writes[tryCatch.getExceptionVariable().getIndex()]++;
                 reads[tryCatch.getExceptionVariable().getIndex()]++;
             }
+
+            for (int succ : dom.outgoingEdges(node)) {
+                stack.push(succ);
+            }
         }
     }
 }