lower-bitint: Handle unreleased SSA_NAMEs from earlier passes gracefully [PR113102]

lower-bitint: Handle unreleased SSA_NAMEs from earlier passes gracefully [PR113102]

On the following testcase earlier passes leave around an unreleased
SSA_NAME - non-GIMPLE_NOP SSA_NAME_DEF_STMT which isn't in any bb.
The following patch makes bitint lowering resistent against those,
the first hunk is where we'd for certain kinds of stmts try to ammend
them and the latter is where we'd otherwise try to remove them,
neither of which works.  The other loops over all SSA_NAMEs either
already also check gimple_bb (SSA_NAME_DEF_STMT (s)) or it doesn't
matter that much if we process it or not (worst case it means e.g.
the pass wouldn't return early even when it otherwise could).

2023-12-22  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/113102
	* gimple-lower-bitint.cc (gimple_lower_bitint): Handle unreleased
	large/huge _BitInt SSA_NAMEs.

	* gcc.dg/bitint-59.c: New test.