If two subscripts has same cast operation (`sext` or `zext`),
`removeMatchingExtensions` strips off them. Due to the following
reasons, remaining this function is not useful and risky:
- If the operand of the cast operation has proper nowrap properties,
SCEV usually strips off the cast operation automatically. It's not very
meaningful to do it on DA side.
- If the operand doesn't have nowrap properties, stripping off the cast
operation may lead to incorrect result. Especially, if it can be
negative, removing `zext` would change the interpretation of the value
in a signed sense.
- This function is part of the root cause of #148435.
Although I've not found any cases where incorrect results are produced
by this function, but I think it doesn't make sense to keep it. As far
as I have checked, there are no regressions after removing this
function.
Resolve#169809
d74617b06f