Optimize if statement to ternary conditional expression

core/src/main/java/org/teavm/ast/optimization/Optimizer.java

@@ -35,14 +35,9 @@ public class Optimizer {
         ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
         stats.analyze(program);
         boolean[] preservedVars = new boolean[stats.writes.length];
-        for (int i = 0; i < preservedVars.length; ++i) {
-            if (stats.writes[i] != 1) {
-                preservedVars[i] = true;
-            }
-        }
         BreakEliminator breakEliminator = new BreakEliminator();
         breakEliminator.eliminate(method.getBody());
-        OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.reads);
+        OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.writes, stats.reads);
         method.getBody().acceptVisitor(optimizer);
         method.setBody(optimizer.resultStmt);
         int paramCount = method.getReference().parameterCount();
@@ -70,17 +65,12 @@ public class Optimizer {
             boolean[] preservedVars = new boolean[method.getVariables().size()];
             ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
             stats.analyze(splitter.getProgram(i));
-            for (int j = 0; j < stats.writes.length; ++j) {
-                if (stats.writes[j] != 1 && stats.reads[j] > 0) {
-                    preservedVars[j] = true;
-                }
-            }
 
             AsyncMethodPart part = method.getBody().get(i);
             BreakEliminator breakEliminator = new BreakEliminator();
             breakEliminator.eliminate(part.getStatement());
             findEscapingLiveVars(liveness, cfg, splitter, i, preservedVars);
-            OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.reads);
+            OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.writes, stats.reads);
             part.getStatement().acceptVisitor(optimizer);
             part.setStatement(optimizer.resultStmt);
         }

core/src/main/java/org/teavm/ast/optimization/OptimizingVisitor.java

@@ -63,12 +63,14 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
     private Expr resultExpr;
     Statement resultStmt;
     private final boolean[] preservedVars;
+    private final int[] writeFrequencies;
     private final int[] readFrequencies;
     private List<Statement> resultSequence;
 
-    OptimizingVisitor(boolean[] preservedVars, int[] readFreqencies) {
+    OptimizingVisitor(boolean[] preservedVars, int[] writeFrequencies, int[] readFrequencies) {
         this.preservedVars = preservedVars;
-        this.readFrequencies = readFreqencies;
+        this.writeFrequencies = writeFrequencies;
+        this.readFrequencies = readFrequencies;
     }
 
     private static boolean isZero(Expr expr) {
@@ -196,6 +198,9 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
     public void visit(VariableExpr expr) {
         int index = expr.getIndex();
         resultExpr = expr;
+        if (writeFrequencies[index] != 1) {
+            return;
+        }
         if (readFrequencies[index] != 1 || preservedVars[index]) {
             return;
         }
@@ -569,8 +574,59 @@ class OptimizingVisitor implements StatementVisitor, ExprVisitor {
         statement.getConsequent().addAll(consequent);
         statement.getAlternative().clear();
         statement.getAlternative().addAll(alternative);
+
+        Statement asConditional = tryConvertToConditionalExpression(statement);
+        if (asConditional != null) {
+            asConditional.acceptVisitor(this);
+        } else {
             resultStmt = statement;
         }
+    }
+
+    private Statement tryConvertToConditionalExpression(ConditionalStatement statement) {
+        if (statement.getConsequent().size() != 1 || statement.getAlternative().size() != 1) {
+            return null;
+        }
+
+        Statement first = statement.getConsequent().get(0);
+        Statement second = statement.getAlternative().get(0);
+        if (!(first instanceof AssignmentStatement) || !(second instanceof AssignmentStatement)) {
+            return null;
+        }
+
+        AssignmentStatement firstAssignment = (AssignmentStatement) first;
+        AssignmentStatement secondAssignment = (AssignmentStatement) second;
+        if (firstAssignment.getLeftValue() == null || secondAssignment.getRightValue() == null) {
+            return null;
+        }
+        if (firstAssignment.isAsync() || secondAssignment.isAsync()) {
+            return null;
+        }
+
+        if (!(firstAssignment.getLeftValue() instanceof VariableExpr)
+                || !(secondAssignment.getLeftValue() instanceof VariableExpr)) {
+            return null;
+        }
+        VariableExpr firstLhs = (VariableExpr) firstAssignment.getLeftValue();
+        VariableExpr secondLhs = (VariableExpr) secondAssignment.getLeftValue();
+        if (firstLhs.getIndex() == secondLhs.getIndex()) {
+            ConditionalExpr conditionalExpr = new ConditionalExpr();
+            conditionalExpr.setCondition(statement.getCondition());
+            conditionalExpr.setConsequent(firstAssignment.getRightValue());
+            conditionalExpr.setAlternative(secondAssignment.getRightValue());
+            conditionalExpr.setLocation(statement.getCondition().getLocation());
+            AssignmentStatement assignment = new AssignmentStatement();
+            assignment.setLocation(conditionalExpr.getLocation());
+            VariableExpr lhs = new VariableExpr();
+            lhs.setIndex(firstLhs.getIndex());
+            assignment.setLeftValue(lhs);
+            assignment.setRightValue(conditionalExpr);
+            writeFrequencies[lhs.getIndex()]--;
+            return assignment;
+        }
+
+        return null;
+    }
 
     @Override
     public void visit(SwitchStatement statement) {

core/src/main/java/org/teavm/backend/javascript/rendering/StatementRenderer.java

@@ -936,7 +936,7 @@ public class StatementRenderer implements ExprVisitor, StatementVisitor {
             expr.getAlternative().acceptVisitor(this);
 
             if (outerPrecedence.ordinal() > Precedence.CONDITIONAL.ordinal()) {
-                writer.append('(');
+                writer.append(')');
             }
 
             if (expr.getLocation() != null) {