I mean, the 8087 was the primary influence on IEEE 754, and hence all of modern floating-point, so in that sense, the numerics people don't ignore it.

The main problem with the x87 floating-point unit is that it only properly works on a weird 80-bit floating-point type that doesn't have the properties you expect of regular IEEE 754 floating-point types, thanks to the explicit integer bit. The design makes it hard to properly emulate the more common 32-bit and 64-bit single and double-precision floating-point arithmetic bit-equivalently, and this is compounded by many compilers' decision to spill floating-point registers incorrectly (they're spilled as 32-bit or 64-bit, not 80-bit), which makes the numerical results of your program effectively random. Also, the size of the 80-bit types isn't really conducive to vectorization, so the floating-point unit gets left behind as SIMD programming starts to become more important.

So what happens is that the x87 is essentially the last of the pre-IEEE 754 floating-point systems that's still hanging around. A lot of the features that would make it interesting in an environment where every vendor has a different floating-point system are now just vestigial weirdness in a world where everybody is following the same floating-point system, and not worth supporting.

The 8087 came out when the premier numerics processors worldwide were the various Cray/CRI products, and if you know this much about the 8087's extended register format then it's likely you already know about Seymour's opinion expressed in silicon about the handling of the LSBs. As a freshly minted computational mathematician I was worried about the Cray systems accuracy on long running computations but after 5 years right on the front lines of the 1-4 highest throughput systems worldwide, with, ISTR, zero practical effect on any computation that ever mattered. Huh turns out Seymour was smarter than me. Should've picked up a shovel.

As far as delivered accuracy of the 8087, performing the operations at 80 bits, rather than 64 it was better than non-extended formats. Anyway you can read all about it here:

https://en.wikipedia.org/wiki/Extended_precision#x86_extende...

Kahan endorsed is all I needed to know.

I can't remember the details from back then but the initial Sun java implementation did something weird with this.

> this is compounded by many compilers' decision to spill floating-point registers incorrectly (they're spilled as 32-bit or 64-bit, not 80-bit)

My compilers behaved properly.