### 7.10 Support for testing GIMPLE passes

As of gcc 7, C functions can be tagged with `__GIMPLE` to indicate that the function body will be GIMPLE, rather than C. The compiler requires the option `-fgimple` to enable this functionality. For example:

    /* { dg-do compile } */
    /* { dg-options "-O -fgimple" } */

    void __GIMPLE (startwith ("dse2")) foo ()
    {
      int a;

    bb_2:
      if (a > 4)
        goto bb_3;
      else
        goto bb_4;

    bb_3:
      a_2 = 10;
      goto bb_5;

    bb_4:
      a_3 = 20;

    bb_5:
      a_1 = __PHI (bb_3: a_2, bb_4: a_3);
      a_4 = a_1 + 4;

      return;
    }

The `startwith` argument indicates at which pass to begin.

Use the dump modifier `-gimple` (e.g. `-fdump-tree-all-gimple`) to make tree dumps more closely follow the format accepted by the GIMPLE parser.

Example DejaGnu tests of GIMPLE can be seen in the source tree at `gcc/testsuite/gcc.dg/gimplefe-*.c`.

The `__GIMPLE` parser is integrated with the C tokenizer and preprocessor, so it should be possible to use macros to build out test coverage.