I think the GP was probably thinking of INTO(0xCE).
https://en.wikipedia.org/wiki/INT_(x86_instruction)#INTO
The bounds-checking was MPX, I think.
> Another extremely useful instruction deleted from x86-64 tested if an array access was in bounds.
https://en.wikipedia.org/wiki/INT_(x86_instruction)#INTO
The bounds-checking was MPX, I think.
> Another extremely useful instruction deleted from x86-64 tested if an array access was in bounds.
Besides, much of the difficulty with memory safety in C and C++ is the existence of pointers (or wrappers around them, like iterators), which do not come with an associated length. Length checking machinery can't help with that problem whether special instructions exist or not.
In short, it's doubtful that the availability of these old instructions would make any difference to the practicality of bounds checking on modern x86 machines whatsoever.
The irony that we need a Lisp Machines solution to fix C and its derived languages.