Reuse more variables in row constructors

Updates RowConstructorCodeGenerator to reuse variables within the same
method scope instead of just locally within the same row constructor
instance. This can significantly reduce the generated code size for
complex expressions involving multiple row constructors within them.

Author: pettyjamesm

core/trino-main/src/main/java/io/trino/sql/gen/RowConstructorCodeGenerator.java

@@ -28,9 +28,7 @@
 import io.trino.sql.relational.RowExpression;
 import io.trino.sql.relational.SpecialForm;
 
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 
 import static io.airlift.bytecode.ParameterizedType.type;
 import static io.airlift.bytecode.expression.BytecodeExpressions.constantFalse;
@@ -70,15 +68,12 @@ public BytecodeNode generateExpression(BytecodeGeneratorContext context)
         Scope scope = context.getScope();
         List<Type> types = rowType.getTypeParameters();
 
-        Variable fieldBlocks = scope.createTempVariable(Block[].class);
+        Variable fieldBlocks = scope.getOrCreateTempVariable(Block[].class);
         block.append(fieldBlocks.set(newArray(type(Block[].class), arguments.size())));
-        // Cache local variable declarations per java type on stack for reuse
-        Map<Class<?>, Variable> javaTypeTempVariables = new HashMap<>();
 
-        Variable blockBuilder = scope.createTempVariable(BlockBuilder.class);
+        Variable blockBuilder = scope.getOrCreateTempVariable(BlockBuilder.class);
         for (int i = 0; i < arguments.size(); ++i) {
             Type fieldType = types.get(i);
-            Variable field = javaTypeTempVariables.computeIfAbsent(fieldType.getJavaType(), scope::createTempVariable);
 
             block.append(blockBuilder.set(constantType(binder, fieldType).invoke(
                     "createBlockBuilder",
@@ -89,16 +84,20 @@ public BytecodeNode generateExpression(BytecodeGeneratorContext context)
             block.comment("Clean wasNull and Generate + " + i + "-th field of row");
             block.append(context.wasNull().set(constantFalse()));
             block.append(context.generate(arguments.get(i)));
+            Variable field = scope.getOrCreateTempVariable(fieldType.getJavaType());
             block.putVariable(field);
             block.append(new IfStatement()
                     .condition(context.wasNull())
                     .ifTrue(blockBuilder.invoke("appendNull", BlockBuilder.class).pop())
                     .ifFalse(constantType(binder, fieldType).writeValue(blockBuilder, field).pop()));
+            scope.releaseTempVariableForReuse(field);
 
             block.append(fieldBlocks.setElement(i, blockBuilder.invoke("build", Block.class)));
         }
+        scope.releaseTempVariableForReuse(blockBuilder);
 
         block.append(newInstance(SqlRow.class, constantInt(0), fieldBlocks));
+        scope.releaseTempVariableForReuse(fieldBlocks);
         block.append(context.wasNull().set(constantFalse()));
         return block;
     }
@@ -112,29 +111,30 @@ private BytecodeNode generateExpressionForLargeRows(BytecodeGeneratorContext con
         Scope scope = context.getScope();
         List<Type> types = rowType.getTypeParameters();
 
-        Variable fieldBuilders = scope.createTempVariable(BlockBuilder[].class);
+        Variable fieldBuilders = scope.getOrCreateTempVariable(BlockBuilder[].class);
         block.append(fieldBuilders.set(invokeStatic(RowConstructorCodeGenerator.class, "createFieldBlockBuildersForSingleRow", BlockBuilder[].class, constantType(binder, rowType))));
 
-        // Cache local variable declarations per java type on stack for reuse
-        Map<Class<?>, Variable> javaTypeTempVariables = new HashMap<>();
-        Variable blockBuilder = scope.createTempVariable(BlockBuilder.class);
+        Variable blockBuilder = scope.getOrCreateTempVariable(BlockBuilder.class);
         for (int i = 0; i < arguments.size(); ++i) {
             Type fieldType = types.get(i);
-            Variable field = javaTypeTempVariables.computeIfAbsent(fieldType.getJavaType(), scope::createTempVariable);
 
             block.append(blockBuilder.set(fieldBuilders.getElement(constantInt(i))));
 
             block.comment("Clean wasNull and Generate + " + i + "-th field of row");
             block.append(context.wasNull().set(constantFalse()));
             block.append(context.generate(arguments.get(i)));
+            Variable field = scope.getOrCreateTempVariable(fieldType.getJavaType());
             block.putVariable(field);
             block.append(new IfStatement()
                     .condition(context.wasNull())
                     .ifTrue(blockBuilder.invoke("appendNull", BlockBuilder.class).pop())
                     .ifFalse(constantType(binder, fieldType).writeValue(blockBuilder, field).pop()));
+            scope.releaseTempVariableForReuse(field);
         }
+        scope.releaseTempVariableForReuse(blockBuilder);
 
         block.append(invokeStatic(RowConstructorCodeGenerator.class, "createSqlRowFromFieldBuildersForSingleRow", SqlRow.class, fieldBuilders));
+        scope.releaseTempVariableForReuse(fieldBuilders);
         block.append(context.wasNull().set(constantFalse()));
         return block;
     }