Re: [PATCH] cprop_hardreg: fix ORIGINAL_REGNO/REG_ATTRS/REG_POINTER handling

[Andrew Pinski <pinskia@gcc.gnu.org>]

On Thu, Jun 22, 2023 at 4:12 AM Philipp Tomsich
<philipp.tomsich@vrull.eu> wrote:
>
> From: Manolis Tsamis <manolis.tsamis@vrull.eu>
>
> Fixes: 6a2e8dcbbd4bab3
>
> Propagation for the stack pointer in regcprop was enabled in
> 6a2e8dcbbd4bab3, but set ORIGINAL_REGNO/REG_ATTRS/REG_POINTER for
> stack_pointer_rtx which caused regression (e.g., PR 110313, PR 110308).
>
> This fix adds special handling for stack_pointer_rtx in the places
> where maybe_mode_change is called. This also adds an check in
> maybe_mode_change to return the stack pointer only when the requested
> mode matches the mode of stack_pointer_rtx.

The only comment I have is on the testcase.

>
>         PR 110308
>
> gcc/ChangeLog:
>
>         * regcprop.cc (maybe_mode_change): Check stack_pointer_rtx mode.
>         (find_oldest_value_reg): Special handling of stack_pointer_rtx.
>         (copyprop_hardreg_forward_1): Ditto.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.dg/torture/pr110308.C: New test.
>
> Signed-off-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
>
> ---
> This addresses both the PRs (110308 and 110313) and was confirmed to
> resolve the AArch64 bootstrap issue reported by Thiago.
>
> OK for trunk?
>
>  gcc/regcprop.cc                         | 43 +++++++++++++++++--------
>  gcc/testsuite/g++.dg/torture/pr110308.C | 30 +++++++++++++++++
>  2 files changed, 60 insertions(+), 13 deletions(-)
>  create mode 100644 gcc/testsuite/g++.dg/torture/pr110308.C
>
> diff --git a/gcc/regcprop.cc b/gcc/regcprop.cc
> index 6cbfadb181f..fe75b7f1fa0 100644
> --- a/gcc/regcprop.cc
> +++ b/gcc/regcprop.cc
> @@ -423,7 +423,7 @@ maybe_mode_change (machine_mode orig_mode, machine_mode copy_mode,
>       It's unclear if we need to do the same for other special registers.  */
>    if (regno == STACK_POINTER_REGNUM)
>      {
> -      if (orig_mode == new_mode)
> +      if (orig_mode == new_mode && new_mode == GET_MODE (stack_pointer_rtx))
>         return stack_pointer_rtx;
>        else
>         return NULL_RTX;
> @@ -487,9 +487,14 @@ find_oldest_value_reg (enum reg_class cl, rtx reg, struct value_data *vd)
>        new_rtx = maybe_mode_change (oldmode, vd->e[regno].mode, mode, i, regno);
>        if (new_rtx)
>         {
> -         ORIGINAL_REGNO (new_rtx) = ORIGINAL_REGNO (reg);
> -         REG_ATTRS (new_rtx) = REG_ATTRS (reg);
> -         REG_POINTER (new_rtx) = REG_POINTER (reg);
> +         if (new_rtx != stack_pointer_rtx)
> +           {
> +             ORIGINAL_REGNO (new_rtx) = ORIGINAL_REGNO (reg);
> +             REG_ATTRS (new_rtx) = REG_ATTRS (reg);
> +             REG_POINTER (new_rtx) = REG_POINTER (reg);
> +           }
> +         else if (REG_POINTER (new_rtx) != REG_POINTER (reg))
> +           return NULL_RTX;
>           return new_rtx;
>         }
>      }
> @@ -965,15 +970,27 @@ copyprop_hardreg_forward_1 (basic_block bb, struct value_data *vd)
>
>                   if (validate_change (insn, &SET_SRC (set), new_rtx, 0))
>                     {
> -                     ORIGINAL_REGNO (new_rtx) = ORIGINAL_REGNO (src);
> -                     REG_ATTRS (new_rtx) = REG_ATTRS (src);
> -                     REG_POINTER (new_rtx) = REG_POINTER (src);
> -                     if (dump_file)
> -                       fprintf (dump_file,
> -                                "insn %u: replaced reg %u with %u\n",
> -                                INSN_UID (insn), regno, REGNO (new_rtx));
> -                     changed = true;
> -                     goto did_replacement;
> +                     bool can_change;
> +                     if (new_rtx != stack_pointer_rtx)
> +                       {
> +                         ORIGINAL_REGNO (new_rtx) = ORIGINAL_REGNO (src);
> +                         REG_ATTRS (new_rtx) = REG_ATTRS (src);
> +                         REG_POINTER (new_rtx) = REG_POINTER (src);
> +                         can_change = true;
> +                       }
> +                     else
> +                       can_change
> +                         = (REG_POINTER (new_rtx) == REG_POINTER (src));
> +
> +                     if (can_change)
> +                       {
> +                         if (dump_file)
> +                           fprintf (dump_file,
> +                                    "insn %u: replaced reg %u with %u\n",
> +                                    INSN_UID (insn), regno, REGNO (new_rtx));
> +                         changed = true;
> +                         goto did_replacement;
> +                       }
>                     }
>                   /* We need to re-extract as validate_change clobbers
>                      recog_data.  */
> diff --git a/gcc/testsuite/g++.dg/torture/pr110308.C b/gcc/testsuite/g++.dg/torture/pr110308.C
> new file mode 100644
> index 00000000000..ddd30d4fc3f
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/torture/pr110308.C
> @@ -0,0 +1,30 @@
> +/* { dg-do compile } */
> +/* { dg-options "-g2 -O2" } */

Since this is in `g++.dg/torture`, you don't need dg-options as the
DG_TORTURE_OPTIONS includes `-O3 -g` already (note `-g` is the same as
`-g2`).

Thanks,
Andrew


> +
> +int channelCount, decodeBlock_outputLength;
> +struct BlockCodec {
> +  virtual int decodeBlock(const unsigned char *, short *);
> +};
> +struct ms_adpcm_state {
> +  char predictorIndex;
> +  int sample1;
> +  ms_adpcm_state();
> +};
> +bool decodeBlock_ok;
> +void encodeBlock() { ms_adpcm_state(); }
> +struct MSADPCM : BlockCodec {
> +  int decodeBlock(const unsigned char *, short *);
> +};
> +void decodeSample(ms_adpcm_state, bool *);
> +int MSADPCM::decodeBlock(const unsigned char *, short *) {
> +  ms_adpcm_state decoderState[2];
> +  ms_adpcm_state *state[2];
> +  state[0] = &decoderState[0];
> +  if (channelCount == 2)
> +    state[1] = &decoderState[0];
> +  short m_coefficients[state[1]->predictorIndex];
> +  for (int i = 0; i < channelCount; i++)
> +    ++state[i]->sample1;
> +  decodeSample(*state[1], &decodeBlock_ok);
> +  return decodeBlock_outputLength;
> +}
> \ No newline at end of file
> --
> 2.34.1
>