Sethi-Ullman register allocation reorders subexpression evaluation to achieve efficient register allocation: https://dl.acm.org/doi/10.1145/321607.321620

With modern register allocators and larger register sets, code generation impact from following source evaluation is of course lower than it used to be. Some CPUs can even involve stack slots in register renaming: https://www.agner.org/forum/viewtopic.php?t=41

On the other hand, even modern Scheme leaves evaluation order undefined. It's not just a C issue.