New subnode ideal optimization: converting "c0 - (x + c1)" into "(c0 - c1) - x"

A DESCRIPTION OF THE PROBLEM :
## Synopsis
New subnode ideal optimization: converting "c0 - (x + c1)" into "(c0 - c1) - x"


## Description
A new ideal optimization can be introduced for subnode: converting "c0 - (x + c1)" into "(c0 - c1) - x".

// Convert "c0 - (x + c1)" into "(c0 - c1) - x"
if (in2->Opcode() == Op_AddI
    && phase->type(in1)->isa_int() != NULL
    && phase->type(in1)->isa_int()->is_con()
    && phase->type(in2->in(2))->isa_int() != NULL
    && phase->type(in2->in(2))->isa_int()->is_con()) {
    jint c0 = phase->type(in1)->isa_int()->get_con();
    jint c1 = phase->type(in2->in(2))->isa_int()->get_con();
  return new SubINode(phase->intcon(java_subtract(c0, c1)), in2->in(1));
}

I have submitted a pull request https://github.com/openjdk/jdk/pull/6441 and included both microbenchmark and jtreg tests.