Re: [RFA] New pass for sign/zero extension elimination

[Dimitar Dimitrov <dimitar@dinux.eu>]

On Sun, Nov 19, 2023 at 05:47:56PM -0700, Jeff Law wrote:
...
> +/* Process uses in INSN.  Set appropriate bits in LIVENOW for any chunks of
> +   pseudos that become live, potentially filtering using bits from LIVE_TMP.
> +
> +   If MODIFIED is true, then optimize sign/zero extensions to SUBREGs when
> +   the extended bits are never read and mark pseudos which had extensions
> +   eliminated in CHANGED_PSEUDOS.  */
> +
> +static void
> +ext_dce_process_uses (rtx insn, bitmap livenow, bitmap live_tmp,
> +		      bool modify, bitmap changed_pseudos)
> +{
> +  /* A nonlocal goto implicitly uses the frame pointer.  */
> +  if (JUMP_P (insn) && find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
> +    {
> +      bitmap_set_range (livenow, FRAME_POINTER_REGNUM * 4, 4);
> +      if (!HARD_FRAME_POINTER_IS_FRAME_POINTER)
> +	bitmap_set_range (livenow, HARD_FRAME_POINTER_REGNUM * 4, 4);
> +    }
> +
> +  subrtx_var_iterator::array_type array_var;
> +  rtx pat = PATTERN (insn);
> +  FOR_EACH_SUBRTX_VAR (iter, array_var, pat, NONCONST)
> +    {
> +      /* An EXPR_LIST (from call fusage) ends in NULL_RTX.  */
> +      rtx x = *iter;
> +      if (x == NULL_RTX)
> +	continue;
> +
> +      /* So the basic idea in this FOR_EACH_SUBRTX_VAR loop is to
> +	 handle SETs explicitly, possibly propagating live information
> +	 into the uses.
> +
> +	 We may continue the loop at various points which will cause
> +	 iteration into the next level of RTL.  Breaking from the loop
> +	 is never safe as it can lead us to fail to process some of the
> +	 RTL and thus not make objects live when necessary.  */
> +      enum rtx_code xcode = GET_CODE (x);
> +      if (xcode == SET)
> +	{
> +	  const_rtx dst = SET_DEST (x);
> +	  rtx src = SET_SRC (x);
> +	  const_rtx y;
> +	  unsigned HOST_WIDE_INT bit = 0;
> +
> +	  /* The code of the RHS of a SET.  */
> +	  enum rtx_code code = GET_CODE (src);
> +
> +	  /* ?!? How much of this should mirror SET handling, potentially
> +	     being shared?   */
> +	  if (SUBREG_BYTE (dst).is_constant () && SUBREG_P (dst))

Shouldn't SUBREG_P be checked first like:
	  if (SUBREG_P (dst) && SUBREG_BYTE (dst).is_constant ())

On pru-unknown-elf with RTL checking I get:

conftest.c:16:1: internal compiler error: RTL check: expected code 'subreg', have 'reg' in ext_dce_process_uses, at ext-dce.cc:421
   16 | }
      | ^
0x158b39e rtl_check_failed_code1(rtx_def const*, rtx_code, char const*, int, char const*)
        /mnt/nvme/dinux/local-workspace/gcc/gcc/rtl.cc:770
0x223a486 ext_dce_process_uses
        /mnt/nvme/dinux/local-workspace/gcc/gcc/ext-dce.cc:421
0x223b5ba ext_dce_process_bb
        /mnt/nvme/dinux/local-workspace/gcc/gcc/ext-dce.cc:651
0x223bdd3 ext_dce
        /mnt/nvme/dinux/local-workspace/gcc/gcc/ext-dce.cc:802
0x223c0ac execute
        /mnt/nvme/dinux/local-workspace/gcc/gcc/ext-dce.cc:868


Regards,
Dimitar