[Farmadupe]

Im assuming the "halt and catch fire" thing is only really possible on pre-microprocessor machines built of discrete components, where the individual parts are small enough to overheat by themselves if driven wrong.

I'd guess the physical CPU package of an i386 would cope just fine with the few (hundreds?) of gates toggling in that small loop.

I wonder if it might be possible to do on a modern FPGA, if you artifically create some unstable circuit and pack deliberately it in a corner of the die?

There's probably some AVX512 concoction that would be the closest equivalent on a modern X64. There's probably an easy experiment -- if that concoction makes CPU freq drop and also makes whole-package thermals drop, it /could/ be due to localized die heating.