https://godbolt.org/z/3TGbK9

It looks like bounds checks are not eliminated when more than one restriction is applied to the index variable (i.e. when it's range checked from two sides). Late edit: It's also interesting that the issue disappears for certain lower limits. For example if idx > 2 && idx < 8 is optimized, while if idx > 5 && idx < 8 is not.

Using assumptions, the bounds checks are removed as expected: https://godbolt.org/z/Ksn8dW
However, if any of the assumptions is a GE or LE instead of a GT or LT, the bounds checks are back: https://godbolt.org/z/YhK1rT