Graybeard, "JD-EE: Normally I find your comments/assessment rational..."
That was immediately after reading the report and before reading anything here. The trim simply followed pilot input, even to the point of becoming silly it was so extreme.
Hal betrayed them by failing to recognize the abrupt decrease in the plane's air speed without any control inputs to have caused it. Rather than declaring a stall Hal should have declared something else, "I'm lost in a maze of twisty little lines instruction code and need you to take command probably to fly pitch and attitude for a short while."
The stall warning created a wrong but apparently predictable reaction in the person flying the plane. Grab sky and grab speed.
I understand that in a more rational world at altitude a genuine stall warning means get the nose down and gain speed then get altitude back. But that never happens so it's never trained for, except it did happen.
Between Hal's erroneous stall warning and the pilot's trained in responses there may well have been no way for the pilots to really figure out what was going o and recover - especially so in that nerve shredded cockpit.
edit: Incidentally, this is not a programmer's problem or error. This is a design inadequacy above their pay grade.
{^_^}