Its true that compilers improve, but i would be willing to bet that if you took the C code and ran it on the original machine there is a good chance that the as

Its true that compilers improve, but i would be willing to bet that if you took the C code and ran it on the original machine there is a good chance that the assembly would out perform it. Hand optimized assembly doesn't necessarily age well, because a large part of the skillset is conforming the code to the processor micro-architecture. Compilers do a lightweight version of this with the -mtune where they utilize tables reflecting the number and type of functional units, instruction latency and throughput, etc to make various tradeoffs in instruction selection and/or placement. The usual "simple" example is a memcpy operation. There are about a dozen different ways (int register moves, utilizing vectors of various sizes, nontemporal, rep movXX, etc) to implement it, and depending on processor, memory subsystem, alignment, and transfer size there can be significant perf diffrences when picking one alternative over another even before considering whether to try prefetch hints, strip mining, or any of the other things that can made a difference. Bottom line, just like playing with differing compilers, and compiler options can easily provide a 2-5x uplift its likely that an expert assembly programmer can gain that much or sometimes significantly more (because they can fundamentally change the algorithm) against a compilers best output, there remain a fair number of things that can be done with hand tuning that compilers simply aren't yet capable of. Since your using SIMD the compiler could be beating it simply because its utilizing one of the wider vector instruction sets vs the original code. Although, for a software package where you don't know the final machine much of this becomes more difficult unless your willing to have a half dozen optimization targets selected at runtime. Bottom, line if it matters that much, there are still people who can take the best code you get out of a C/C++ compiler and generally provide an uplift. Whether its worth the effort, that is another question.