RFR: 8279607: Existing optimization "~x+1" -> "-x" can be generalized to "~x+c" -> "(c-1)-x". [v3]

[Zhiqiang Zang]

> Hi all,
> 
> Existing optimization `~x+1 -> -x` can be generalized to `~x+c -> (c-1)-x`. I included both microbenchmark and jtreg tests.
> 
> 
> // Convert (~x+c) into (c-1)-x. Note there isn't a bitwise not
> // bytecode, "~x" would typically represented as "x^(-1)", so (~x+c)
> // will be (x^(-1))+c.
> if (op1 == Op_Xor(bt) &&
>     (in2->Opcode() == Op_ConI || in2->Opcode() == Op_ConL) &&
>     phase->type(in1->in(2)) == TypeInteger::minus_1(bt)) {
>   Node* c_minus_one = phase->makecon(add_ring(phase->type(in(2)), TypeInteger::minus_1(bt)));
>   return SubNode::make(c_minus_one, in1->in(1), bt);
> }
> 
> 
> Thank you for reviewing.

Zhiqiang Zang has updated the pull request incrementally with one additional commit since the last revision:

  transform ~(x+c) to (-c-1)-x.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6858/files
  - new: https://git.openjdk.java.net/jdk/pull/6858/files/5c9bcfd8..c540be30

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6858&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6858&range=01-02

  Stats: 247 lines in 3 files changed: 180 ins; 2 del; 65 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6858.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6858/head:pull/6858

PR: https://git.openjdk.java.net/jdk/pull/6858