I'm developing a small program that utilizes Windows API functions, and I want to handle any failures effectively. If a function fails, I need to log which function failed, move to another function to print the error in hexadecimal, and then exit the program. Since these are standard cryptography, file I/O, and console I/O functions, I don't anticipate frequent failures.
I'm trying to decide whether it's better to create a branch in my code for error handling or to use the cmov instruction to avoid branching completely, despite introducing some extra instructions.
The original flow involves testing a register to see if it's non-zero and jumping to an error branch if it is, moving strings to the stack before jumping to the exit. The proposed method would use cmov to move the error string directly into registers without branching first, then execute the error handling loop and exit. However, I'm unsure how to weigh the benefits of each approach. I originally thought both methods had one branch, but now I'm questioning which one is actually more efficient.
6 Answers
I've dealt with performance optimizations in assembly before. In one of my projects, my compiler struggled with large graphs that the linker couldn't handle, which made me go lower level with assembly. Ultimately, I hit a bottleneck with my instruction cache. Sometimes, unrolling loops can be beneficial if you're going beyond the cache size, so performance can vary.
For your case, avoid over-optimizing high-level I/O operations; modern CPUs are significantly faster than disk access times anyway.
You mentioned trying to avoid branches, but in cases where branches are predictable, there's generally no need to optimize for the unlikely case. If you expect things to behave a certain way, sticking with the original approach might actually make more sense here.
You might want to rethink your strategy here. It doesn't seem like you are tackling the problem in the most effective way.
Are you really writing a Windows API program and delving into assembly? That seems a bit over the top for typical application development!
Optimizing CPU usage for I/O operations seems a bit overkill. Remember, the bottlenecks in I/O are usually not from the CPU side but from the speed of the disk, which is much slower. Focus on optimizing where it truly counts.
The best way to determine which approach is better is by doing performance profiling. If you're really focused on performance, it's useful to profile at runtime and choose the method that runs faster on your specific machine. However, this only makes sense if you’re working in a performance-critical inner loop where every millisecond counts.
True! But the performance differences might not matter much once you're making a call to the Windows API; that usually takes longer than the optimizations we’re discussing. Focus on tight loops when it comes to these kinds of optimizations.
Gotcha! Looks like I’ll need to dig deeper into performance tools.
What actually makes a branch predictable versus unpredictable? Is there a general rule of thumb?