4 ms·

And here we again have the assertion that ARM engineers think very hard and therefore never make mistakes. Do you think Intel engineers don't think very hard?

And here we again have the assertion that ARM engineers think very hard and therefore never make mistakes. Do you think Intel engineers don't think very hard? Oops, Pentium 4. Oops Itanium. And that was after Pentium Pro wiped the floor with DEC, Sun, MIPS and the rest. ARM engineers are mortal too.

klelatti 5y ago
That's not what I said! Rather its vanishingly unlikely they would discard an ISA feature that was one of the reasons for Arm's success (Thumb was key in ARM7TDMI getting into Nokia etc) casually and without a great deal of analysis of real world code. And there is no evidence whatsoever of an advantage of the order of 20% that the original comment stated. Pointing to Intel's errors (the disasters of iAPX432 and Itanium are probably more pertinent) really just highlights how consistently Arm have got ISA design right over the years.
- brucehoult 5y ago
  ARM have got a long list of discarded or ignored technologies too. They've had several attempts at SIMD, and even when they did SVE it turned out that the "Scalable" didn't extend down to microcontrollers like RISC-V's V extension does and they've had to introduce the slightly different and incompatible MVE as well to cover that. It will be interesting to see what happens in a few years when some applications start to want vector registers longer than 4096 bits, the upper limit by design of SVE's scalability. And then there are things such as Jazelle and T2EE. I firmly believe -- and have since it was announced in 2012 -- that the fixed length nature of aarch64 will eventually prove to be a mistake. Code density is important. They could do a mode like Thumb in the ARM7TDMI (which I have a ton of experience with), but it was Thumb2 in the Cortex series which really propelled ARM to their current heights. There is no room in the aarch64 encoding to do a Thumb2. It would need an entirely new ISA encoding. I think what probably happened is ARM managed to roughly match the (pretty awful) code density of x86_64 with a fixed length encoding and decided that was good enough as x86_64 was the only competition they were going to face in the 64 bit space. Except it's not.
  - klelatti 5y ago
    I believe that if you’re going to accuse someone of making a huge mistake - especially someone with a lot more experience - then you’d better have some solid evidence to back it up. You may think and believe these things but you still have no actual evidence for these or for the performance claims being made in this thread.

klelatti 5y ago

That's not what I said! Rather its vanishingly unlikely they would discard an ISA feature that was one of the reasons for Arm's success (Thumb was key in ARM7TDMI getting into Nokia etc) casually and without a great deal of analysis of real world code. And there is no evidence whatsoever of an advantage of the order of 20% that the original comment stated. Pointing to Intel's errors (the disasters of iAPX432 and Itanium are probably more pertinent) really just highlights how consistently Arm have got ISA design right over the years.

brucehoult 5y ago
ARM have got a long list of discarded or ignored technologies too. They've had several attempts at SIMD, and even when they did SVE it turned out that the "Scalable" didn't extend down to microcontrollers like RISC-V's V extension does and they've had to introduce the slightly different and incompatible MVE as well to cover that. It will be interesting to see what happens in a few years when some applications start to want vector registers longer than 4096 bits, the upper limit by design of SVE's scalability. And then there are things such as Jazelle and T2EE. I firmly believe -- and have since it was announced in 2012 -- that the fixed length nature of aarch64 will eventually prove to be a mistake. Code density is important. They could do a mode like Thumb in the ARM7TDMI (which I have a ton of experience with), but it was Thumb2 in the Cortex series which really propelled ARM to their current heights. There is no room in the aarch64 encoding to do a Thumb2. It would need an entirely new ISA encoding. I think what probably happened is ARM managed to roughly match the (pretty awful) code density of x86_64 with a fixed length encoding and decided that was good enough as x86_64 was the only competition they were going to face in the 64 bit space. Except it's not.
- klelatti 5y ago
  I believe that if you’re going to accuse someone of making a huge mistake - especially someone with a lot more experience - then you’d better have some solid evidence to back it up. You may think and believe these things but you still have no actual evidence for these or for the performance claims being made in this thread.