Improve drawergen to only recompile the object file if its timestamp does not match

tools/drawergen/drawergen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawspancodegen.h"
 #include "fixedfunction/drawwallcodegen.h"
 #include "fixedfunction/drawcolumncodegen.h"
@@ -618,6 +619,18 @@ std::string LLVMProgram::DumpModule()
 
 /////////////////////////////////////////////////////////////////////////////
 
+std::string &AllTimestamps()
+{
+	static std::string timestamps;
+	return timestamps;
+}
+
+void AddSourceFileTimestamp(const char *timestamp)
+{
+	if (!AllTimestamps().empty()) AllTimestamps().push_back(' ');
+	AllTimestamps() += timestamp;
+}
+
 int main(int argc, char **argv)
 {
 	if (argc != 2)
@@ -626,6 +639,25 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	std::string timestamp_filename = argv[1] + std::string(".timestamp");
+
+	FILE *file = fopen(timestamp_filename.c_str(), "rb");
+	if (file != nullptr)
+	{
+		char buffer[4096];
+		int bytes_read = fread(buffer, 1, 4096, file);
+		fclose(file);
+		std::string last_timestamp;
+		if (bytes_read > 0)
+			last_timestamp = std::string(buffer, bytes_read);
+
+		if (AllTimestamps() == last_timestamp)
+		{
+			std::cout << "Not recompiling drawers because the object file is already up to date." << std::endl;
+			exit(0);
+		}
+	}
+
 	llvm::install_fatal_error_handler([](void *user_data, const std::string& reason, bool gen_crash_diag)
 	{
 		std::cerr << "LLVM fatal error: " << reason;
@@ -640,7 +672,7 @@ int main(int argc, char **argv)
 
 	LLVMDrawers drawersSSE2(cpuName, "_SSE2");
 
-	FILE *file = fopen(argv[1], "wb");
+	file = fopen(argv[1], "wb");
 	if (file == nullptr)
 	{
 		std::cerr << "Unable to open " << argv[1] << " for writing." << std::endl;
@@ -656,6 +688,20 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	file = fopen(timestamp_filename.c_str(), "wb");
+	if (file == nullptr)
+	{
+		std::cerr << "Could not create timestamp file" << std::endl;
+		return 1;
+	}
+	result = fwrite(AllTimestamps().data(), AllTimestamps().length(), 1, file);
+	fclose(file);
+	if (result != 1)
+	{
+		std::cerr << "Could not write timestamp file" << std::endl;
+		return 1;
+	}
+
 	//LLVMDrawers drawersSSE4("core2");
 	//LLVMDrawers drawersAVX("sandybridge");
 	//LLVMDrawers drawersAVX2("haswell");

tools/drawergen/fixedfunction/drawcolumncodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawcolumncodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/fixedfunction/drawercodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawercodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/fixedfunction/drawskycodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawskycodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/fixedfunction/drawspancodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawspancodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/fixedfunction/drawtrianglecodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawtrianglecodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/fixedfunction/drawwallcodegen.cpp

@@ -21,6 +21,7 @@
 */
 
 #include "precomp.h"
+#include "timestamp.h"
 #include "fixedfunction/drawwallcodegen.h"
 #include "ssa/ssa_function.h"
 #include "ssa/ssa_scope.h"

tools/drawergen/timestamp.h

@@ -0,0 +1,12 @@
+
+#pragma once
+
+void AddSourceFileTimestamp(const char *timestamp);
+
+namespace
+{
+	struct TimestampSourceFile
+	{
+		TimestampSourceFile() { AddSourceFileTimestamp(__TIME__); }
+	} timestamp;
+}