[Bug rtl-optimization/64037] [4.8/4.9/5 Regression] Miscompilation with -Os and enum class : char parameter

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64037

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Miscompilation with -Os and |[4.8/4.9/5 Regression]
                   |enum class : char parameter |Miscompilation with -Os and
                   |                            |enum class : char parameter

--- Comment #13 from H.J. Lu <hjl.tools at gmail dot com> ---
The bug was introduced by

https://gcc.gnu.org/ml/gcc-cvs/2007-09/msg00613.html

commit 5d93234932c3d8617ce92b77b7013ef6bede9508
Author: shinwell <shinwell@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Thu Sep 20 11:01:18 2007 +0000

      gcc/
      * combine.c: Include cgraph.h.
      (setup_incoming_promotions): Rework to allow more aggressive
      elimination of sign extensions when all call sites of the
      current function are known to lie within the current unit.


    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@128618
138bc75d-0d04-0410-961f-82ee72b054a4

Before this commit, combine.c has

          enum machine_mode mode = TYPE_MODE (TREE_TYPE (arg));
          int uns = TYPE_UNSIGNED (TREE_TYPE (arg));

          mode = promote_mode (TREE_TYPE (arg), mode, &uns, 1);
          if (mode == GET_MODE (reg) && mode != DECL_MODE (arg))
            {
              rtx x;
              x = gen_rtx_CLOBBER (DECL_MODE (arg), const0_rtx);
              x = gen_rtx_fmt_e ((uns ? ZERO_EXTEND : SIGN_EXTEND), mode, x);
              record_value_for_reg (reg, first, x);
            }

It matches function.c:

  /* This is not really promoting for a call.  However we need to be
     consistent with assign_parm_find_data_types and expand_expr_real_1.  */
  promoted_nominal_mode
    = promote_mode (data->nominal_type, data->nominal_mode, &unsignedp, 1);

128618 changed

mode = promote_mode (TREE_TYPE (arg), mode, &uns, 1);

to

mode3 = promote_mode (DECL_ARG_TYPE (arg), mode2, &uns3, 1);

It breaks none WORD_REGISTER_OPERATIONS targets.