bitint: Handle BIT_FIELD_REF lowering [PR114157]

bitint: Handle BIT_FIELD_REF lowering [PR114157]

The following patch adds support for BIT_FIELD_REF lowering with
large/huge _BitInt lhs.  BIT_FIELD_REF requires mode argument first
operand, so the operand shouldn't be any huge _BitInt.
If we only access limbs from inside of BIT_FIELD_REF using constant
indexes, we can just create a new BIT_FIELD_REF to extract the limb,
but if we need to use variable index in a loop, I'm afraid we need
to spill it into memory, which is what the following patch does.
If there is some bitwise type for the extraction, it extracts just
what we need and not more than that, otherwise it spills the whole
first argument of BIT_FIELD_REF and uses MEM_REF with an offset
with VIEW_CONVERT_EXPR around it.

2024-03-05  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114157
	* gimple-lower-bitint.cc: Include stor-layout.h.
	(mergeable_op): Return true for BIT_FIELD_REF.
	(struct bitint_large_huge): Declare handle_bit_field_ref method.
	(bitint_large_huge::handle_bit_field_ref): New method.
	(bitint_large_huge::handle_stmt): Use it for BIT_FIELD_REF.

	* gcc.dg/bitint-98.c: New test.
	* gcc.target/i386/avx2-pr114157.c: New test.
	* gcc.target/i386/avx512f-pr114157.c: New test.