I disagree.

An optimization that speeds a program by x2 has the same effect as running on a faster CPU. An optimization that packs things tighter into memory has the same effect as using more memory.

Program semantics are usually referred to as “all output given all input, for any input configuration” but ignoring memory use or CPU time, provided they are both finite (but not limited).

TCE easily converts a program that will halt, regardless of available memory, to one that will never halt, regardless of available memory. That’s a big change in both theoretical and practical semantics.

I probably won’t argue that a change that reduces an O(n^5) space/time requirement to an O(1) requirement is a change in semantics, even though it practically is a huge change. But TCE changes a most basic property of a finite memory Turing machine (halts or not).

We don’t have infinite memory Turing machines.

edited: Turing machine -> finite memory Turing machine.