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    <p>The assembler doesn't move anything, that's the domain of a compiler optimizations (at compile time), or Jitters at runtime if such exist (when dealing with java or other jitted languages).<br> An interpreter is often a far simpler construct, that's in charge of taking a single instruction at a time and executing it on some host system (doing along the way the translation from one architecture to the other, or from bytecode into machine code). It's theoretically possible to build an interpreter that can shuffle code but that's a bit redundant since jitted languages can recompile the entire code and get this reorder as part of it. It's also not very useful since baseline interpreted run mode is already very slow on the host CPU due to the overhead, that simple code shuffle tricks are hardly going to make a dent on the performance.</p> <p>Also note that on modern HW, most of the simple reordering is pointless - an out-or-order execution engine will rearrange the code internally anyway so that each instruction can be executed once its data dependencies are resolved. For control dependency there are really good branch predictors in the market, so you hardly stall - you just speculate and flush in case you were wrong (which is worth it as the prediction accuracy could get around ~95% in most cases).</p> <p>There's still important benefit for reordering, but it's not for eliminating bubbles, it's mostly for load hoisting, loop-invariant code motion and eliminating memory false dependencies that the HW can't reorder itself. However, this isn't a simple reorder you can do at interpretation time, you'll need actual compilation or jitting for that.</p>
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    1. POCan interpreted languages use delay slots?
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    1. USLeeor
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      1. VTUpMod
    1. CONiggle: The Stanford MIPS used an assembler to do limited instruction reordering (and packing). "assembly language instruction set, defines instructions that are unpacked and have no pipeline dependencies or branch delays." ("Design of a High Performance VLSI Processor", Hennessy et al., 1983, TR#236). The intention was to allow assembly-level compatibility and implementation-specific machine code while allowing changes in implementation. (This is mostly just a historical footnote.)
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      1. USPaul A. Clayton
    2. CO@PaulA.Clayton, there are many dataflow and VLIW architectures that allow you to perform your code with predetermined dependencies, so you may reorder the code as you see fit. I think most of them employ dedicated compilers that do most of that work for you.
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