[ajross]

> Have lots of weird old x86 instructions you are forced to support but no one actually uses? Don't waste transistors on them

That's been the role of microcode for like three decades now. Why does it matter if the instruction no one uses is implemented with FPGA gates or uops? No one uses them.

[webmobdev]

Theoretically, Now you can create "micro-codes" in the CPU for your specific needs - e.g. scientists do a lot of calulation and would like a processor optimised for that. Now they can use the FPGA to do it. You want a CPU instruction that is optimised for something else - you can program the FPGA for that.

[asimpletune]

Or maybe a compiler could recognize that optimization is possible and create it for you

[Kuinox]

More likely a JIT can do that.

[LeifCarrotson]

The FPGA can't be reprogrammed fast enough for the JIT approach to work, unless you're running computations that take many minutes or hours. I suppose that does apply to some workloads, but it would be tough to ask your JIT to solve the halting problem and guess whether a workload will last 10 seconds or take longer than that.

[penteract]

For a JIT, the easy way to guess is to wait until it's already taken 10 seconds and if it hasn't stopped, assume it will take at least 10 more.

[Kuinox]

I would say that program that are run and exit immediatly are a minority of what is produced with languages. A lot of web server, services, gui are produced in JIT languages and have a timespan of multiple minutes. AFAIK FPGA reprogrammation time depends on the size of your edit, and your hardware, the article says that they expect to reprogramm it on a program load, so I don't think it will be that slow.

[bcrosby95]

Why can't a JIT program the FPGA based upon previous runs through the same set of code? IIRC the JVM won't rest on its final optimizations until it runs a chunk of code hundreds (or thousands? I forget) of times.

[pjmlp]

Depends pretty much on which JVM we are talking about, Java is like C, plenty to chose from.

In what concerns OpenJDK that is configurable via the -XX flags.

[snicker7]

In scientific computing, that is the typical workload. That is why, say, Julia exists despite having a ridiculous JIT overhead.

[chippiewill]

Isn't that a general warm-up problem with JITs though?

[pjmlp]

With any kind of compilation process, a balancing act between time spend waiting and the quality of generated machine code.

[robomartin]

I've been doing that for years. I have created custom microcoded CPU's in FPGA's for tasks where it would provide an advantage. One example I remember was a microcoded real time image warping engine.

[pjmlp]

Six actually, given that microcode was the approach taken on most mainframes that started around Burroughs timeframe.