Improved and simplified loop optimizations.

Rationale:
This CL merges some common cases into one, thereby simplifying
the code quite a bit. It also prepares for more general induction
cycles (rather than the simple phi-add currently used). Finally,
it generalizes the closed form elimination with empty loops.
As a result of the latter, elaborate but weird code like:

  private static int waterFall() {
    int i = 0;
    for (; i < 10; i++);
    for (; i < 20; i++);
    for (; i < 30; i++);
    for (; i < 40; i++);
    for (; i < 50; i++);
    return i;
  }

now becomes just this (on x86)!

    mov eax, 50
    ret

Change-Id: I8d22ce63ce9696918f57bb90f64d9a9303a4791d
Test: m test-art-host

0 files changed, 0 insertions, 0 deletions