RFR: 8261812: C2 compilation fails with assert(!had_error) failed: bad dominance

[Roland Westrelin]

In the testByte() test case, byteField is assigned int values that
don't fit in a byte.

obj.byteField = (byte)(1 << i);

At parse time, c2 expands this to (in pseudo code):

int v = (1 << i);
obj.byteField = (v << 24) >> 24;

next:

StoreBNode::Ideal() runs and StoreNode::Ideal_sign_extended_input()
causes this to become:

obj.byteField = (1 << i);

i is then constant folded to 9:

obj.byteField = 512;

obj doesn't escape and is scalarized. The value of the byteField needs
to be recorded in the debug info. Because there are 2 such a store, a
Phi is created:

(Phi 512 1024)

The Phi is created with type TypeInt::BYTE. Because that doesn't
overlap with the input values, the Phi is transformed to top. The test
case then triggers a deoptimization and a crash occurs in the
deoptimization code.

The failure of the bug report is not a crash during deoptimization but
a c2 crash. The root cause is the same but in that case a chain of Phi
is involved and when one becomes top, it causes an uncommon trap to
have an input that doesn't dominate the uncommon trap.

I noticed LoadBNode::Ideal() re-inserts the 2 shifts when it returns a
value from a Store. I propose the same fix here in the allocation
elimination code.

Same problem applies to short and char. They are covered by the fix. I
also included boolean even though I don't see how to trigger the
failure with it.

-------------

Commit messages:
 - test & fix

Changes: https://git.openjdk.java.net/jdk/pull/2774/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2774&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261812
  Stats: 172 lines in 6 files changed: 149 ins; 2 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2774.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2774/head:pull/2774

PR: https://git.openjdk.java.net/jdk/pull/2774