BIT_FIELD_REF is currently only generated by the middle-end (fold, SRA and parts of the vectorizer). At the moment the bit position and size of the extract can be non-constant and the type of the result is unspecified.
I suggest to make sure that bit position and size are constants, the object referenced is of integral type (BIT_FIELD_REF should not be used as a way to circumvent aliasing) and the result type is of the same type as the operand zero type (and not a bitfield type of the referenced size -- in which case the BIT_FIELD_REF_UNSIGNED would be useless). The result would then be properly extended according to BIT_FIELD_REF_UNSIGNED. Is this how it was intended? fold currently optimizes a.b.c == 0 to BIT_FIELD_REF <a, 8, big-num> & 1 for bit field field-decls c. IMHO this is bad because it pessimizes TBAA (needs to use a's alias set, not the underlying integral type alias set) and it "breaks" type correctness as arbitrary structure types appear as operand zero. ? Thanks, Richard.
