[Bug tree-optimization/103857] New: implement ternary without jump (and comparison)

["drepper.fsp+rhbz at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103857

            Bug ID: 103857
           Summary: implement ternary without jump (and comparison)
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: drepper.fsp+rhbz at gmail dot com
  Target Milestone: ---

This test case is derived from actual code and I expect it to be not uncommon
in general.  Maybe not exactly in this form but perhaps the matcher can catch a
few more cases.

Take this code:

extern void g(int);
void f1(int* a, int b, int c)
{
  for (unsigned i = 0; i < 100; ++i)
    g(a[i] == b ? c : b);
}
void f2(int* a)
{
  for (unsigned i = 0; i < 100; ++i)
    g(a[i] == 42 ? 10 : 42);
}


The function 'g' is called in each loop with one of two values which is the
opposite from the one that is match in the condition of the ternary operation. 
This allows the respective loops to be rewritten as

  for (unsigned i = 0; i < 100; ++i)
    g(a[i] ^ c ^ b);

and

  for (unsigned i = 0; i < 100; ++i)
    g(a[i] ^ 10 ^ 42);

In the former case the c ^ b operation can be hoisted.

This should be faster and smaller in pretty much all situations and on all
platforms.