cfgexpand: Rewrite add_scope_conflicts_2 to use cache and look back further [PR111422]

After fixing loop-im to do the correct overflow rewriting
for pointer types too. We end up with code like:
```
_9 = (unsigned long) &g;
_84 = _9 + 18446744073709551615;
_11 = _42 + _84;
_44 = (signed char *) _11;
...
*_44 = 10;
g ={v} {CLOBBER(eos)};
...
n[0] = &f;
*_44 = 8;
g ={v} {CLOBBER(eos)};
```

Which was not being recongized by the scope conflicts code.
This was because it only handled one level walk backs rather than multiple ones.
This fixes the issue by having a cache which records all references to addresses
of stack variables.

Unlike the previous patch, this only records and looks at addresses of stack variables.
The cache uses a bitmap and uses the index as the bit to look at.

	PR middle-end/117426
	PR middle-end/111422
gcc/ChangeLog:

	* cfgexpand.cc (struct vars_ssa_cache): New class.
	(vars_ssa_cache::vars_ssa_cache): New constructor.
	(vars_ssa_cache::~vars_ssa_cache): New deconstructor.
	(vars_ssa_cache::create): New method.
	(vars_ssa_cache::exists): New method.
	(vars_ssa_cache::add_one): New method.
	(vars_ssa_cache::update): New method.
	(vars_ssa_cache::dump): New method.
	(add_scope_conflicts_2): Factor mostly out to
	vars_ssa_cache::operator(). New cache argument.
	Walk the bitmap cache for the stack variables addresses.
	(vars_ssa_cache::operator()): New method factored out from
	add_scope_conflicts_2. Rewrite to be a full walk of all operands
	and use a worklist.
	(add_scope_conflicts_1): Add cache new argument for the addr cache.
	Just call add_scope_conflicts_2 for the phi result instead of calling
	for the uses and don't call walk_stmt_load_store_addr_ops for phis.
	Update call to add_scope_conflicts_2 to add cache argument.
	(add_scope_conflicts): Add cache argument and update calls to
	add_scope_conflicts_1.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr117426-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>