This reverts commit fa7eb6ee and
provides alternative fix for opt/boolopt4.c.

This fixes backend/subregister.c.

Except for global CSE, comparing nodes of different block always results
in 'not equal', so we should consider them for hashing beforehand.

Simply directly check the magnitude of the tarval instead of converting it to a long.
* On 64 bit hosts 32 bit operations could not match immediates with bit 31 set.
  E.g. v32 & 0xFFFFFFF0.
* On 32 bit hosts 64 bit operations with 32 bit non-negative constants were erroneously matched and caused silent miscompilation.
  E.g. v64 & 0xFFFFFFF0.
* On 32 bit hosts 64 bit operations with constants, which would fit into 32 bits, but have higher bits set, were not matched, because get_tarval_long() failed.
  E.g. v64 & 0xFFFFFFFFFFFFFFF0.

This fixes opt/boolopt4.c.

amd64: Change the parameter 'can_match_ip_relative' of match_immediate_32() to 'must_match_ip_relative'.

Either a user must have a ip-relative address or it must not.

This fixes opt/fehler318.c.

The computation of dominance might invalidate out edges.

This fixes opt/fehler319.c.

Dominance is computed explicitly later.

Otherwise repeatedly invoking be_main() leads to a double free.

They previously used be_stack_layout but that structure will be remove
soon.

We can just as well make up names on the fly while printing the entities
for debugging.

The soon to be introduced spillslot entities can be at negative offset,
so the previously used -1 as convention for invalid offsets is not a
good idea anymore.