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Compiler optimizers also optimize only the generated code, but not the data structure layout, which is usually what matters most. Also, compilers often can't o

Compiler optimizers also optimize only the generated code, but not the data structure layout, which is usually what matters most. Also, compilers often can't optimize stuff which is obvious to humans. E.g. here is an example of GCC not being able to delete useless code: <https://godbolt.org/z/655KeM33Y https://godbolt.org/z/655KeM33Y> (it's fixed in later versions of GCC, but this version of GCC also isn't that old). Another example is Clang emitting useless code out of nowhere: <https://youtu.be/R5tBY9Zyw6o?t=1620 https://youtu.be/R5tBY9Zyw6o?t=1620>. So, it's not out of the ordinary for compilers to be really stupid about the assembly they generate.

lhorie 5y ago
JIT compilers like V8 are able to optimize from Object hashmaps to structs, but the problem is that it has trouble figuring out how to group arbitrary object literals into the same bucket in order to get monomorphism guarantees (this is a very common pattern among projects that emit large data structures such as JS parser projects like babel for example) This is partly a reason why virtual dom projects don't expose the ability to replace a virtual dom node constructor with inline literals despite it being a pure deterministic function.