bitint: Handle VCE from large/huge _BitInt SSA_NAME from load [PR114156]

bitint: Handle VCE from large/huge _BitInt SSA_NAME from load [PR114156]

When adding checks in which case not to merge a VIEW_CONVERT_EXPR from
large/huge _BitInt to vector/complex etc., I missed the case of loads.
Those are handled differently later.
Anyway, I think the load case is something we can handle just fine,
so the following patch does that instead of preventing the merging
gimple_lower_bitint; we'd then copy from memory to memory and and do the
vce only on the second one, it is just better to vce the first one.

2024-03-01  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114156
	* gimple-lower-bitint.cc (bitint_large_huge::lower_stmt): Allow
	rhs1 of a VCE to have no underlying variable if it is a load and
	handle that case.

	* gcc.dg/bitint-96.c: New test.