Since Bads have modes now the check for mode_X initialized the bitinfo,
which results in incorrect reachability information.

Broken with csmith 2.0.0 seed 909842313
in libFirm 1953ce88

convopt: fix potential bug with modulo shifts, improve cost calculation for optimizable conv(shift) combinations

Fixes C/unkept_loop.c

The functionality already existed,
but this is necessary at more than on place.

        Cond
       /    \
  projA      projB   =>   Jmp     Bad
       \    /                \   /
       block                 block

This optimization might produce more empty blocks to remove,
which in turn might enable more Cond=>Jmp opts.
So we need to perform this until nothing changes anymore.

Fixes x86code/cfopt.c
Breaks C/unkept_loop.c, because ifconv cannot handle Bads

This code does nothing, because the previous commit removed the
equivalent_node_Block function.

Fixes opt/localopts2

Because of Phis blocks cannot be equivalent. The cfopt must do all
block merging.

For example, consider the case where block A has one predecessor
block B, which contains a Jmp. Naively, we might exchange(A,B).
However, A might contain a Phi with one operand, then the graph
is broken afterwards, since we move the Phi into B as well.

- The pns of X_regular and X_except are annotated in the opcode now.
- The memory input is annotated in the opcode now
- only nodes with X_regular, X_except are marked fragile

We can still use ia32 ShlD, ShrD functions by matching Or(Shl,Shr)
patterns in the ia32 transformer.