RFR: 8257531: Super word not applied to a loop of simple Buffer operations

[Vladimir Kozlov]

In Buffer case there is additional (loop invariant) load from java/nio/IntBuffer.offset field.
SuperWord did not handle loop's invariants in complex address expressions (only when vectorization is forced):

`AddP(addr, AddP(addr, addr, LShiftL(ConvI2L(CastII(AddI(AddI(iv_phi, invariant_LoadI), incr))), shift)), 16)`

Invariant reference is used to make sure all memory accesses in vectors use the same one. And only when alignment code is generated in pre-loop it is used for code generatin. But that code did not take into account that invariant have to be scaled if needed as in this example (invariant_LoadI << shift).

I propose to record scaling (left shift) for invariant when it is present and use it to compare invariants and in pre-loop alignment code generation. I also slightly modified tracing output code for invariants.

This allow vectorize Java code which uses Buffer.

I added new test based on @PaulSandoz example. It tests presence of new vectors and correctness of vectorized code.
I included case (ByteBuffer.allocateDirect()) which is not vectorized because it uses Unsafe access - SuperWord complains about CastX2P(AddL) nodes which it sees instead of AddP.  We may consider vectorizing such code too later.

Testing: tier1-4, precheckin-comp (-Xcomp), renaissance test

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Commit messages:
 - 8257531: Super word not applied to a loop of simple Buffer operations

Changes: https://git.openjdk.java.net/jdk/pull/1618/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1618&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257531
  Stats: 264 lines in 3 files changed: 241 ins; 2 del; 21 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1618.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1618/head:pull/1618

PR: https://git.openjdk.java.net/jdk/pull/1618