GDScript: Don't re-evaluate index on assigment with operation

Pass the calculated index from the stack and use the same to get and set
the value. This avoids a function with side effects being evaluated
twice when using indexing in an assignment with operation statement
(e.g. a[function()] += 1).

modules/gdscript/gdscript_compiler.cpp

@@ -90,11 +90,11 @@ bool GDScriptCompiler::_create_unary_operator(CodeGen &codegen, const GDScriptPa
 	return true;
 }
 
-bool GDScriptCompiler::_create_binary_operator(CodeGen &codegen, const GDScriptParser::OperatorNode *on, Variant::Operator op, int p_stack_level, bool p_initializer) {
+bool GDScriptCompiler::_create_binary_operator(CodeGen &codegen, const GDScriptParser::OperatorNode *on, Variant::Operator op, int p_stack_level, bool p_initializer, int p_index_addr) {
 
 	ERR_FAIL_COND_V(on->arguments.size() != 2, false);
 
-	int src_address_a = _parse_expression(codegen, on->arguments[0], p_stack_level, false, p_initializer);
+	int src_address_a = _parse_expression(codegen, on->arguments[0], p_stack_level, false, p_initializer, p_index_addr);
 	if (src_address_a < 0)
 		return false;
 	if (src_address_a & GDScriptFunction::ADDR_TYPE_STACK << GDScriptFunction::ADDR_BITS)
@@ -171,7 +171,7 @@ GDScriptDataType GDScriptCompiler::_gdtype_from_datatype(const GDScriptParser::D
 	return result;
 }
 
-int GDScriptCompiler::_parse_assign_right_expression(CodeGen &codegen, const GDScriptParser::OperatorNode *p_expression, int p_stack_level) {
+int GDScriptCompiler::_parse_assign_right_expression(CodeGen &codegen, const GDScriptParser::OperatorNode *p_expression, int p_stack_level, int p_index_addr) {
 
 	Variant::Operator var_op = Variant::OP_MAX;
 
@@ -205,7 +205,7 @@ int GDScriptCompiler::_parse_assign_right_expression(CodeGen &codegen, const GDS
 		return _parse_expression(codegen, p_expression->arguments[1], p_stack_level, false, initializer);
 	}
 
-	if (!_create_binary_operator(codegen, p_expression, var_op, p_stack_level, initializer))
+	if (!_create_binary_operator(codegen, p_expression, var_op, p_stack_level, initializer, p_index_addr))
 		return -1;
 
 	int dst_addr = (p_stack_level) | (GDScriptFunction::ADDR_TYPE_STACK << GDScriptFunction::ADDR_BITS);
@@ -214,7 +214,7 @@ int GDScriptCompiler::_parse_assign_right_expression(CodeGen &codegen, const GDS
 	return dst_addr;
 }
 
-int GDScriptCompiler::_parse_expression(CodeGen &codegen, const GDScriptParser::Node *p_expression, int p_stack_level, bool p_root, bool p_initializer) {
+int GDScriptCompiler::_parse_expression(CodeGen &codegen, const GDScriptParser::Node *p_expression, int p_stack_level, bool p_root, bool p_initializer, int p_index_addr) {
 
 	switch (p_expression->type) {
 		//should parse variable declaration and adjust stack accordingly...
@@ -704,7 +704,9 @@ int GDScriptCompiler::_parse_expression(CodeGen &codegen, const GDScriptParser::
 						return from;
 
 					int index;
-					if (named) {
+					if (p_index_addr != 0) {
+						index = p_index_addr;
+					} else if (named) {
 						if (on->arguments[0]->type == GDScriptParser::Node::TYPE_SELF && codegen.script && codegen.function_node && !codegen.function_node->_static) {
 
 							GDScriptParser::IdentifierNode *identifier = static_cast<GDScriptParser::IdentifierNode *>(on->arguments[1]);
@@ -1091,7 +1093,7 @@ int GDScriptCompiler::_parse_expression(CodeGen &codegen, const GDScriptParser::
 							codegen.alloc_stack(slevel);
 						}
 
-						int set_value = _parse_assign_right_expression(codegen, on, slevel + 1);
+						int set_value = _parse_assign_right_expression(codegen, on, slevel + 1, named ? 0 : set_index);
 						if (set_value < 0) //error
 							return set_value;
 

modules/gdscript/gdscript_compiler.h

@@ -140,12 +140,12 @@ class GDScriptCompiler {
 	void _set_error(const String &p_error, const GDScriptParser::Node *p_node);
 
 	bool _create_unary_operator(CodeGen &codegen, const GDScriptParser::OperatorNode *on, Variant::Operator op, int p_stack_level);
-	bool _create_binary_operator(CodeGen &codegen, const GDScriptParser::OperatorNode *on, Variant::Operator op, int p_stack_level, bool p_initializer = false);
+	bool _create_binary_operator(CodeGen &codegen, const GDScriptParser::OperatorNode *on, Variant::Operator op, int p_stack_level, bool p_initializer = false, int p_index_addr = 0);
 
 	GDScriptDataType _gdtype_from_datatype(const GDScriptParser::DataType &p_datatype) const;
 
-	int _parse_assign_right_expression(CodeGen &codegen, const GDScriptParser::OperatorNode *p_expression, int p_stack_level);
-	int _parse_expression(CodeGen &codegen, const GDScriptParser::Node *p_expression, int p_stack_level, bool p_root = false, bool p_initializer = false);
+	int _parse_assign_right_expression(CodeGen &codegen, const GDScriptParser::OperatorNode *p_expression, int p_stack_level, int p_index_addr = 0);
+	int _parse_expression(CodeGen &codegen, const GDScriptParser::Node *p_expression, int p_stack_level, bool p_root = false, bool p_initializer = false, int p_index_addr = 0);
 	Error _parse_block(CodeGen &codegen, const GDScriptParser::BlockNode *p_block, int p_stack_level = 0, int p_break_addr = -1, int p_continue_addr = -1);
 	Error _parse_function(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready = false);
 	Error _parse_class_level(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);