Fix null check elimination

The existing null check elimination mechanism suffered from the same
limitation as the SSA renaming: it took shortcuts that were valid in
a trace compilation world, but not in a method compilation world.

This CL replaces the old mechanism, and additionally takes advantage
of some the fact that "this" is always non-null, as are objects returned
from OP_NEW_* (thanks Ian!).

Two test cases added.  The one for ensuring that unnecessary null checks
are elminated requires manual inspection.  The other - that we don't
eliminate a necessary null check - is disabled until exceptions are working.

Change-Id: I2a9b72741f56617bf609e4d7c20244796c988f28
15 files changed
tree: 1141a3f0f91c527dfe28796e88f166d2bc0ed7fd
  2. build/
  3. src/
  4. test/
  5. tools/