Avoid re-analyzing SymbolReferences

Optimizers such as DesugaringOptimizer and SimplifyExpressions
need access to expression types, which is currently re-computed
every time. This change improves the process by short-circuiting
the analysis for SymbolReferences.

presto-main/src/main/java/com/facebook/presto/sql/planner/optimizations/DesugaringOptimizer.java

@@ -28,6 +28,7 @@
 import com.facebook.presto.sql.planner.plan.TableScanNode;
 import com.facebook.presto.sql.tree.Expression;
 import com.facebook.presto.sql.tree.ExpressionTreeRewriter;
+import com.facebook.presto.sql.tree.SymbolReference;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Maps;
 
@@ -110,6 +111,9 @@ public PlanNode visitTableScan(TableScanNode node, RewriteContext<Void> context)
 
         private Expression desugar(Expression expression)
         {
+            if (expression instanceof SymbolReference) {
+                return expression;
+            }
             IdentityHashMap<Expression, Type> expressionTypes = getExpressionTypes(session, metadata, sqlParser, types, expression);
             return ExpressionTreeRewriter.rewriteWith(new DesugaringRewriter(expressionTypes), expression);
         }

presto-main/src/main/java/com/facebook/presto/sql/planner/optimizations/SimplifyExpressions.java

@@ -37,6 +37,7 @@
 import com.facebook.presto.sql.tree.LogicalBinaryExpression;
 import com.facebook.presto.sql.tree.NotExpression;
 import com.facebook.presto.sql.tree.NullLiteral;
+import com.facebook.presto.sql.tree.SymbolReference;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -146,6 +147,9 @@ public PlanNode visitTableScan(TableScanNode node, RewriteContext<Void> context)
 
         private Expression simplifyExpression(Expression expression)
         {
+            if (expression instanceof SymbolReference) {
+                return expression;
+            }
             expression = ExpressionTreeRewriter.rewriteWith(new PushDownNegationsExpressionRewriter(), expression);
             expression = ExpressionTreeRewriter.rewriteWith(new ExtractCommonPredicatesExpressionRewriter(), expression, NodeContext.ROOT_NODE);
             IdentityHashMap<Expression, Type> expressionTypes = getExpressionTypes(session, metadata, sqlParser, types, expression);