lower-bitint: Lower FLOAT_EXPR from BITINT_TYPE INTEGER_CST [PR112679]

lower-bitint: Lower FLOAT_EXPR from BITINT_TYPE INTEGER_CST [PR112679]

The bitint lowering pass only does something if it sees BITINT_TYPE (medium,
large, huge) SSA_NAMEs.  In the past I've already ran into one special case
where the above doesn't work well, if there is a store of medium/large/huge
BITINT_TYPE INTEGER_CST into memory, there might not be any BITINT_TYPE
SSA_NAMEs in the function, yet we need to lower.  This has been solved by
also checking for SSA_NAME_IS_VIRTUAL_OPERAND if at the vdef there isn't
such a store (the whole intent is make the pass as cheap as possible in the
currently very likely case that the IL doesn't have any BITINT_TYPEs at
all).
And the following testcase shows a similar problem.  With -frounding-math
we don't fold some of FLOAT_EXPRs with INTEGER_CST operands, and if those
INTEGER_CSTs are medium/large/huge BITINT_TYPEs, we need to either cast
the INTEGER_CST to corresponding INTEGER_TYPE (for medium) or lower to
internal fn call which is later turned into libgcc call (for large/huge).
The following patch does that, but of course admittedly this discovery
of stores and FLOAT_EXPRs means we already look through quite a few
SSA_NAME_DEF_STMTs even when BITINT_TYPEs never appear.

2023-11-23  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/112679
	* gimple-lower-bitint.cc (gimple_lower_bitint): Also stop first loop on
	floating point SSA_NAME set in FLOAT_EXPR assignment from BITINT_TYPE
	INTEGER_CST.  Set has_large_huge for those if that BITINT_TYPE is large
	or huge.  Set kind to such FLOAT_EXPR assignment rhs1 BITINT_TYPE's kind.

	* gcc.dg/bitint-42.c: New test.