When truncating a sub-HVX-width vector to a boolean vector (e.g., v64i8
-> v64i1 in 128-byte HVX mode), the operation would crash with
"Unhandled HVX operation" UNREACHABLE. This happened because the
condition in LowerHvxOperationWrapper/ReplaceHvxNodeResults did not
handle the case where the input vector needs widening and the result is
a boolean vector.
The fix adds WidenHvxTruncateToBool which widens the input to HVX
register width (e.g., v64i8 -> v128i8), performs the truncate to widened
bool type (v128i8 -> v128i1), extracts the result subvector (v128i1 ->
v64i1).
This allows the widened truncate to match the existing V6_vandvrt
pattern in HexagonPatternsHVX.td.
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