Wilco (Wilco.Dijkstra.delete@this.ntlworld.com) on November 19, 2012 9:31 am wrote:
[snip]
> That certainly helps, but you're still doing it multiple times on targets which may not have a lot of
> resources. What is more efficient - every phone compiling every bit of software you download, or just
> run a highly optimized binary which was compiled once with optimal settings on fast hardware?

For systems that download all software that is not pre-installed, why couldn't the server provide a binary optimized for the particular system? (The application developer might provide a virtual machine binary to the distributor [to minimize costs for the developer and validation costs for the distributor], but the distributor could cache highly optimized translations.)

In theory, such could provide substantial freedom from ISA constraints and perhaps even facilitate microarchitectural optimizations which might be impractical with a single binary. (Fat binaries would seem to be unattractive because of the bandwidth waste.) In theory, performance- (or storage-) intensive features could be enabled when one upgrades one's hardware. It is not clear how the economics of this would work; for a vertically integrated system, the benefit to the distributor of encouraging hardware upgrades and bandwidth/services use might be passed on to the application developer through reduced hosting fees for software with such bonus features or a small payback on upgrade (for some applications, a loss in software upgrade fees might be compensated by marketing advantages of end-user simplicity or an increase in use [if linked to advertising or a pay-per-use service]). (There might even be some place for optimization for typical or critical use, so that the same software might be translated differently for different uses on the same hardware.) If the distributor's compilers improved (e.g., better support of offloading to an accelerator, autovectorization, autoparallelization), subscribing to a distributor could have added value beyond simply tracking licenses and backing up software.

I am curious about what the ideal virtual machine binary representation would be like. I am guessing that such would include much more information that a machine binary would include (to ease validation and optimization for different targets). If the VM was optimized for server-side compilation to system-specific binaries, some characteristics that make interpretation easier might be avoided.