driver: add --hash-seed

kernel/driver.cc

@@ -18,6 +18,7 @@
  */
 
 #include "kernel/yosys.h"
+#include "kernel/hashlib.h"
 #include "libs/sha1/sha1.h"
 #include "libs/cxxopts/include/cxxopts.hpp"
 #include <iostream>
@@ -269,6 +270,8 @@ int main(int argc, char **argv)
 	options.add_options("developer")
 		("X,trace", "enable tracing of core data structure changes. for debugging")
 		("M,randomize-pointers", "will slightly randomize allocated pointer addresses. for debugging")
+		("hash-seed", "mix up hashing values with <seed>, for extreme optimization and testing",
+			cxxopts::value<int>(), "<seed>")
 		("A,abort", "will call abort() at the end of the script. for debugging")
 		("x,experimental", "do not print warnings for the experimental <feature>",
 			cxxopts::value<std::vector<std::string>>(), "<feature>")
@@ -415,6 +418,10 @@ int main(int argc, char **argv)
 		if (result.count("infile")) {
 			frontend_files = result["infile"].as<std::vector<std::string>>();
 		}
+		if (result.count("hash-seed")) {
+			int seed = result["hash-seed"].as<int>();
+			Hasher::set_fudge(seed);
+		}
 
 		if (log_errfile == NULL) {
 			log_files.push_back(stdout);

kernel/hashlib.h

@@ -80,13 +80,20 @@ class Hasher {
 		// traditionally 5381 is used as starting value for the djb2 hash
 		state = 5381;
 	}
+	static void set_fudge(uint32_t f) {
+		fudge = f;
+	}
 
 	private:
 	uint32_t state;
+	static uint32_t fudge;
 	// The XOR version of DJB2
 	[[nodiscard]]
 	static uint32_t mkhash(uint32_t a, uint32_t b) {
-		return ((a << 5) + a) ^ b;
+		uint32_t hash = ((a << 5) + a) ^ b;
+		if (fudge)
+			hash = fudge ^ mkhash_xorshift(hash);
+		return hash;
 	}
 	public:
 	void hash32(uint32_t i) {

kernel/yosys.cc

@@ -92,6 +92,7 @@ std::set<std::string> yosys_input_files, yosys_output_files;
 bool memhasher_active = false;
 uint32_t memhasher_rng = 123456;
 std::vector<void*> memhasher_store;
+uint32_t Hasher::fudge = 0;
 
 std::string yosys_share_dirname;
 std::string yosys_abc_executable;