Maybe that's because JIT is almost always used in languages that were slowed in the first place, e.g. due to GC.
Is there a JITing C compiler, or something like that? Would that even make sense?
Dynamo: A Transparent Dynamic Optimization System https://dl.acm.org/doi/pdf/10.1145/358438.349303
> We describe the design and implementation of Dynamo, a software dynamic optimization system that is capable of transparently improving the performance of a native instruction stream as it executes on the processor. The input native instruction stream to Dynamo can be dynamically generated (by a JIT for example), or it can come from the execution of a statically compiled native binary. This paper evaluates the Dynamo system in the latter, more challenging situation, in order to emphasize the limits, rather than the potential, of the system. Our experiments demonstrate that even statically optimized native binaries can be accelerated Dynamo, and often by a significant degree. For example, the average performance of -O optimized SpecInt95 benchmark binaries created by the HP product C compiler is improved to a level comparable to their -O4 optimized version running without Dynamo. Dynamo achieves this by focusing its efforts on optimization opportunities that tend to manifest only at runtime, and hence opportunities that might be difficult for a static compiler to exploit. Dynamo's operation is transparent in the sense that it does not depend on any user annotations or binary instrumentation, and does not require multiple runs, or any special compiler, operating system or hardware support. The Dynamo prototype presented here is a realistic implementation running on an HP PA-8000 workstation under the HPUX 10.20 operating system.
https://www.semanticscholar.org/paper/Dynamo%3A-a-transparen...
For purely array-based code, JIT is the only factor and Java can seriously compete with C/C++. It's impossible to be competitive with idiomatic Java code though.
C# has structs (value classes) if you bother to use them. Java has something allegedly similar with Project Valhalla, but my observation indicates they completely misunderstand the problem and their solution is worthless.
Hahah spicy take, I'd be interested to hear more. It definitely might not bode well that they opened the "Generics Reification" talk at JVMLS 2024 with "we have no answers, only problems."
* The compiler isn't actually guaranteed to store them by value at all. Basically, they're written to be an "optional extension" rather than a first-class feature in their own right.
* Everything is forced to be immutable, so you can't actually write most of the code that would take advantage of value types in the first place. Hot take: functional programming is mainly a bad workaround for languages that don't support value types in the first place.
(I suppose if the list of things you can do with structs is very short, this will be nowhere near as useful but will also reduce the amount of compiler changes)
Random jars taken out of Maven central should be able to continue to execute in a Valhala enabled JVM, without changes in their original semantics, while at the same time being able somewhat to take advantage of the Valhala world.
Naturally there is always the issue of APIs that no longer exist like Thread.stop(), but that is orthogonal to the idea to have binary libraries keep working in a new value aware world.
There are tons of compiler changes, minimal semantic changes and keeping bytecode ABI as much as possible is the engineering challenge.
But I'd posit that one programming pattern enabled by a GC is concurrent programming. Java can happily create a bunch of promises/futures, throw them at a thread pool and let that be crunched without worrying about the lifetimes of stuff sent in or returned from these futures.
For single threaded stuff, C probably has java beat on memory and runtime. However, for multithreading it's simply easier to crank out correct threaded code in Java than it is in C.
IMO, this is what has made Go so appealing. Go doesn't produce the fastest binaries on the planet, but it does have nice concurrency primitives and a GC that makes highly parallel processes easy.
For languages like rust/C/C++, thread safe data structures are VERY hard to pull off. That's because tracking the lifetime of things tracked by the data structures introduces all sorts of heartburn.
What GCed languages buy you is not needing to track those lifetimes. Yes, you can still have data races and shared memory mutation problems, but you can also write thread safe data structures like caches without the herculean efforts needed to communicate with users of the cache who owns what when and when that thing dies.
The best that Rust and C++ can do to solve these problems is ARC and a LOT of copying.
Yes, for example, compiling C to JavaScript (or asm.js, etc. [0]) leads to the C code being JITed.
And yes, there are definitely benchmarks where this is actually faster. Any time that a typical C compiler can't see that inlining makes sense is such an opportunity, as the JIT compiler sees the runtime behavior. The speedup can be very large. However, in practice, most codebases get inlined well using clang/gcc/etc., leaving few such opportunities.
[0] This may also happen when compiling C to WebAssembly, but it depends on whether the wasm runtime does JIT optimizations - many do not and instead focus on static optimizations, for simplicity.
People have been doing runtime code generation for a very long time for exactly this reason.
A general implementation faster than, say, g++ is a completely different beast.
Two weights, two measures.
If you want to further discuss what is what, lets see how up to date is your ISO knowledge, versus the plethora of extensions across C and C++ compilers.