[Bug rtl-optimization/127630] New: Add match.pd RTL generator

[kaelfandrew at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127630

            Bug ID: 127630
           Summary: Add match.pd RTL generator
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kaelfandrew at gmail dot com
  Target Milestone: ---

Noticed from
https://gcc.gnu.org/pipermail/gcc-patches/2026-September/732648.html

Allow match.pd to produce RTL code, maybe via RTL macro like GIMPLE/GENERIC
macros.

match.pd has

/* ~~x -> x */
(simplify
  (bit_not (bit_not @0))
  (non_lvalue @0))

while simplify-rtx.cc has

simplify_context::simplify_unary_operation_1
...
    case NOT:
      /* (not (not X)) == X.  */
      if (GET_CODE (op) == NOT)
        return XEXP (op, 0);