## Problem
`RemoveDeadValues` can legally drop dead function arguments on private
`func.func` callees. But call-sites to such functions aren't fixed if
the call operation keeps its call arguments in a **segmented operand
group** (i.ie, uses `AttrSizedOperandSegments`), unless the call op
implements `getArgOperandsMutable` and the RDV pass actually uses it.
## Fix
When RDV decides to drop callee function args, it should, for each
call-site that implements `CallOpInterface`, **shrink the call's
argument segment** via `getArgOperandsMutable()` using the same dead-arg
indices. This keeps both the flat operand list and the
`operand_segment_sizes` attribute in sync (that's what
`MutableOperandRange` does when bound to the segment).
## Note
This change is a no-op for:
* call ops without segment operands (they still get their flat operands
erased via the generic path)
* call ops whose calle args weren't dropped (public, external,
non-`func-func`, unresolved symbol, etc)
* `llvm.call`/`llvm.invoke` (RDV doesn't drop `llvm.func` args
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Co-authored-by: Mehdi Amini <joker.eph@gmail.com>
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