English is not my native language and I wrote a bit too fast the message: I wanted to say that "everything pushing forward RISC-V is good".
I code RISC-V assembly, I don't use C machine instructions (I don't even use the pseudo-instructions, ABI register names and dodge nearly all ISA extensions, I try to stick to core as much as I can). I run my code on x86_64 linux with a small interpreter written in x86_64 assembly (thx to the 'R' in RISC).
I wonder if there are some 'broad and not niche, real-life' speed benchmark numbers to show how much C machine instructions are worth.
For the moment, I see those C machine instructions more as a marketing extension to match their arm equivalent: you know, for those key deciding people who care more about the amount of features and not their contextual pertinent usage.
To say an ISA is "good" is related to some set of technical sweet spots based on compromises based on projected usages.
RVA from my point of view is mostly preparing RISC-V hardware for some level of x86_64/arm compatibility.
I wonder if there are RISC-V implementations using the latest silicon process from TSMC.
Aarch64 dropped thumb instructions.
I don't think you're going to find a single benchmark on the effectiveness of compressed instructions since it really depends deeply on both the workload and the whole system. For example, memory bandwidth and cache pressure are both important for whether smaller text sizes matter, and that may depend on what else is running at the same time.
Note your assembler may be automatically compressing instructions without you asking. You'll have to disassemble the binary to find out.