This is an intuitive step and I kind of did something similar initially (I simplified the diagram a lot, but it was basically what you are suggesting). However, it slowed down the computed goto interpreter by 6% (though not the tail calling interpreter).
The other comment about interpreters being greatly affected by instruction cache is right. The other problem is that PGO in CPython's test suite could be improved and when you have the full thing as a switch-case and trigger the profiling mode, PGO then mistakenly thinks that the RECORD_INST_X section is hot (when it is clearly not). This causes a pessimization in the interpreter loop leading to the 6% slowdown.
The other comment about interpreters being greatly affected by instruction cache is right. The other problem is that PGO in CPython's test suite could be improved and when you have the full thing as a switch-case and trigger the profiling mode, PGO then mistakenly thinks that the RECORD_INST_X section is hot (when it is clearly not). This causes a pessimization in the interpreter loop leading to the 6% slowdown.