lower-bitint: Fix up handle_operand_addr INTEGER_CST handling [PR113361]

lower-bitint: Fix up handle_operand_addr INTEGER_CST handling [PR113361]

As the testcase shows, the INTEGER_CST handling in handle_operand_addr
(i.e. what is used when passing address of an integer to a bitint library
routine) wasn't correct.  If the minimum precision to represent an
INTEGER_CST is smaller or equal to limb_prec, the code correctly uses
m_limb_type; if the minimum precision of a _BitInt INTEGER_CST is large
enough such that the bitint is middle, large or huge, everything is fine
too.  But the code wasn't handling correctly e.g. __int128 constants which
need more than limb_prec bits or _BitInt constants which on the architecture
are considered small (say have DImode limb_mode, TImode abi_limb_mode and
for [65, 128] bits use TImode scalar like the proposed aarch64 patch).
Best would be to use an array of 2/3/4 limbs in that case, but we'd need to
convert the INTEGER_CST to a CONSTRUCTOR in the right endianity etc.,
so the code was using mid_min_prec to enforce a middle _BitInt precision.
Except that mid_min_prec can be 0 and not computed yet, or it doesn't have
to be the smallest middle _BitInt precision, just the smallest so far
encountered.  So, on the testcase one possibility was that it used precision
65 from mid_min_prec, even when the INTEGER_CST actually needed larger
minimum precision (96 bits at least), or crashed when mid_min_prec was 0.

The patch fixes it in 2 hunks, the first makes sure we actually try to
create a BITINT_TYPE for the > limb_prec cases like __int128, and the second
instead of using mid_min_prec attempts to increase mp precision until it
isn't small anymore.

2024-01-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/113361
	* gimple-lower-bitint.cc (bitint_large_huge::handle_operand_addr):
	Fix up determination of the type for > limb_prec constants.

	* gcc.dg/torture/bitint-47.c: New test.