There isn't much the compiler can optimize on such a simple CPU as the m68k when the source is simple C or hand-optimized assembler code to begin with.
Contemporary compilers definitely do a lot of CPU-agnostic optimizations that ye olde compilers weren't capable of. The only new CPU features that fundamentally change this are vector instructions, and compilers still suck at autovectorization.
Contemporary compilers are "optimized" to optimize for superscalar, fully pipelined, out of order cpus with plenty of ram and caches. Literally nothing in common with a 68k. Also modern compilers wouldn't even know how to produce code for the amiga coprocessors.
This engine very likely is written in hand optimized, clock-exact, asm.