diff --git a/README.md b/README.md
index ce07e9d..0ad74f5 100644
--- a/README.md
+++ b/README.md
@@ -75,7 +75,10 @@ Call that from your main program to run inference. Function parameters are named
 Using the compiler `-ffast-math` (or equivalent) when compiling onnx2c-generated code increases computation speed.
 See the [GCC wiki on floating point maths](https://gcc.gnu.org/wiki/FloatingPointMath) for details.
 
-Onnx2c has an [experimental quantization option](quantization.md) to convert floating point calculation to integers.
+Onnx2c has a few optimization passes that modify the generated output:
+ - Tensor unionization to wrap intermediate tensors in unions to help the compiler re-use the heap memory.
+ - Optimization for AVR processors to put constants into instruction memory.
+ - An [experimental quantization option](quantization.md) to convert floating point calculation to integers.
 
 `./onnx2c -h` prints out all available command line options.
 
diff --git a/src/main.cc b/src/main.cc
index 88e1d49..0e5bbdd 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -24,7 +24,8 @@ int main(int argc, const char *argv[])
 
 	std::cout.precision(20);
 	toC::Graph toCgraph(onnx_model);
-	toCgraph.unionize_tensors();
+	if( options.opt_unionize )
+		toCgraph.unionize_tensors();
 	toCgraph.print_source(std::cout);
 }
 
diff --git a/src/options.cc b/src/options.cc
index 60119d6..b0cc197 100644
--- a/src/options.cc
+++ b/src/options.cc
@@ -64,12 +64,54 @@ void store_define_option(const std::string &opt)
 	options.dim_defines[name] = val_num;
 }
 
+void print_optimization_passes(void)
+{
+	std::cout << "Available optimization passes:" << std::endl;
+	std::cout << " - 'unionize' (defaut:on)" << std::endl;
+	std::cout << " - 'none' (disable all optimization passes)" << std::endl;
+}
+
+void store_optimization_passes(const std::string &opt)
+{
+	LOG(TRACE) << "Parsing optimizations: " << opt << std::endl;
+
+	// disable all optimizations (i.e. override the default settings)
+	// then enable those that were requested
+	options.opt_unionize=false;
+	if( opt == "none" )
+	{
+		LOG(TRACE) << "Disabling all optimizations: " << opt << std::endl;
+		return;
+	}
+
+	if( opt == "help" )
+	{
+		print_optimization_passes();
+		exit(0);
+	}
+	std::vector<std::string> result;
+	std::stringstream ss (opt);
+	std::string item;
+	while (getline (ss, item, ',')) {
+		if( item == "unionize" )
+		{
+			LOG(DEBUG) << "Enabling 'Unionize tensors' optimization pass" << std::endl;
+			options.opt_unionize=true;
+		}
+		else {
+			LOG(WARNING) << "Optimization pass " << item << " does not exist" << std::endl;
+		}
+	}
+	LOG(TRACE) << "That was all optimizations" << std::endl;
+}
+
 void parse_cmdline_options(int argc, const char *argv[])
 {
 	args::ArgumentParser parser("Generate C code from an ONNX graph file.");
 	args::Flag avr(parser, "avr", "Target AVR-GCC", {'a', "avr"});
 	args::ValueFlagList<std::string> define(parser, "dim:size", "Define graph input dimension. Can be given multiple times", {'d', "define"});
 	args::ValueFlag<int> loglevel(parser, "level", "Logging verbosity. 0(none)-4(all)", {'l',"log"});
+	args::ValueFlag<std::string> optimizations(parser, "opt[,opt]...", "Specify optimization passes to run. ('help' to list available)", {'p', "optimizations"});
 	args::Flag help(parser, "help", "Print this help text.", {'h',"help"});
 	args::Flag quantize(parser, "quantize", "Quantize network (EXPERIMENTAL!)", {'q', "quantize"});
 	args::Flag version(parser, "version", "Print onnx2c version", {'v', "version"});
@@ -109,6 +151,7 @@ void parse_cmdline_options(int argc, const char *argv[])
 			store_define_option(d);
 		}
 	}
+	if (optimizations) { store_optimization_passes( args::get(optimizations) ); }
 	if (input) { options.input_file = args::get(input); }
 	if (options.input_file == "" ) { std::cerr << "No input file given"; hint_at_help_and_exit(); }
 }
diff --git a/src/options.h b/src/options.h
index a1e70f7..59e1789 100644
--- a/src/options.h
+++ b/src/options.h
@@ -11,6 +11,7 @@ struct onnx2c_opts
 {
 	bool quantize=false;
 	bool target_avr=false;
+	bool opt_unionize=true;
 	/*
 	 * logging levels are
 	 * cmd line     aixlog     Use
diff --git a/src/util.cc b/src/util.cc
index 5047000..f309c93 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -6,9 +6,6 @@
 #include "tensor.h"
 #include "util.h"
 
-// command line option
-extern bool target_avr;
-
 std::string cify_name(const std::string &in)
 {
 	// Replace all non-allowed characters with underscore
diff --git a/test/onnx_backend_tests_generator.cc b/test/onnx_backend_tests_generator.cc
index 9bd71de..7a9b70f 100644
--- a/test/onnx_backend_tests_generator.cc
+++ b/test/onnx_backend_tests_generator.cc
@@ -72,6 +72,9 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 
+	options.logging_level = 1;
+	AixLog::Log::init<AixLog::SinkCerr>(AixLog::Severity::error);
+
 	onnx::ModelProto onnx_model;
 	std::string dir(argv[1]);