RFR: 8263971: C2 crashes with SIGFPE with -XX:+StressGCM and -XX:+StressIGVN

[Roland Westrelin]

For the inner for loop of the test case:

1- the control input of the DivI node in the loop body is cleared
  because the range of values for i23, the loop's iv, is known to
  never be null.

2- pre/main/post loops are added

3- the main loop is unrolled enough that it's fully unrolled but
  actually never entered

4- because the main loop is no longer a looop, DiVI nodes from the
main loop can float and are scheduled in the pre loop.

5- the main loop is never executed (the values of the iv for the main
loop after unrolling fall outside the (3, 68] range of values of the
initial loop), one of the main loop DivI nodes divides by 0 and
because it doesn't stay in the main loop, the crash occurs.

The calls to PhaseIdealLoop::cast_incr_before_loop() in
PhaseIdealLoop::insert_pre_post_loops() should guarantee that nodes
that uses the loop iv stay control dependent on the test that guards
the main loop. For that it inserts a CastII node with the
_carry_dependency flag set. With 8256730, that CastII for the main
loop is pushed through the iv AddI of the pre loop. In the process, it
looses the _carry_dependency flag which causes the CastII node to be
optimized out and the DivI nodes to float.

With the proposed fix, CastII nodes created by the logic from 8256730
have the _carry_dependency flag set if the CastII node that's
transform has it.

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Commit messages:
 - test
 - fix

Changes: https://git.openjdk.java.net/jdk/pull/3190/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3190&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263971
  Stats: 70 lines in 2 files changed: 65 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3190.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3190/head:pull/3190

PR: https://git.openjdk.java.net/jdk/pull/3190