Hello Vineet:
Version 7 of the patch incorporates the below review comments.
Please review.
Thanks & Regards
Ajit
On 19/09/23 1:57 am, Vineet Gupta wrote:
> Hi Ajit,
>
> On 9/17/23 22:59, Ajit Agarwal wrote:
>> This new version of patch 6 use improve ree pass for rs6000 target using
>> defined ABI interfaces.
>> Bootstrapped and regtested on power64-linux-gnu.
>>
>> Review comments incorporated.
>>
>> Thanks & Regards
>> Ajit
>
> Nit: This seems to belong to "what changed in v6" between the two "---" lines
> right before start of source diff.
>
>> ree: Improve ree pass for rs6000 target using defined abi interfaces
>>
>> For rs6000 target we see redundant zero and sign extension and done to
>> improve ree pass to eliminate such redundant zero and sign extension
>> using defined ABI interfaces.
>
> It seems you have redundant "redundant zero and sign extension" - pun
> intended ;-)
>
> On a serious note, when debugging your code for a possible RISC-V benefit, it
> seems what it is trying to do is address REE giving up due to "missing
> definition(s)". Perhaps mentioning that in commitlog would give the reader
> more context.
>
>> +/* Return TRUE if target mode is equal to source mode of zero_extend
>> + or sign_extend otherwise false. */
>> +
>> +static bool
>> +abi_target_promote_function_mode (machine_mode mode)
>> +{
>> + int unsignedp;
>> + machine_mode tgt_mode =
>> + targetm.calls.promote_function_mode (NULL_TREE, mode, &unsignedp,
>> + NULL_TREE, 1);
>> +
>> + if (tgt_mode == mode)
>> + return true;
>> + else
>> + return false;
>> +}
>> +
>> +/* Return TRUE if the candidate insn is zero extend and regno is
>> + an return registers. */
>
> Additional Whitespace and grammer
> s/an return registers/a return register
>
> Please *run* contrib/check_gnu_style on your patch before sending out on
> mailing lists, saves reviewers time and they can focus more on technical
> content.
>
>> +
>> +static bool
>> +abi_extension_candidate_return_reg_p (rtx_insn *insn, int regno)
>> +{
>> + rtx set = single_set (insn);
>> +
>> + if (GET_CODE (SET_SRC (set)) != ZERO_EXTEND)
>> + return false;
>
> This still has ABI assumptions: RISC-V generates SIGN_EXTEND for functions
> args and return reg.
> This is not a deficiency of patch per-se, but something we would like to
> address - even if as an addon-patch.
>
>> +
>> + if (FUNCTION_VALUE_REGNO_P (regno))
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> +/* Return TRUE if reg source operand of zero_extend is argument registers
>> + and not return registers and source and destination operand are same
>> + and mode of source and destination operand are not same. */
>> +
>> +static bool
>> +abi_extension_candidate_p (rtx_insn *insn)
>> +{
>> + rtx set = single_set (insn);
>> +
>> + if (GET_CODE (SET_SRC (set)) != ZERO_EXTEND)
>> + return false;
> Ditto: ABI assumption.
>
>> +
>> + machine_mode ext_dst_mode = GET_MODE (SET_DEST (set));
>
> why not simply @dst_mode
>
>> + rtx orig_src = XEXP (SET_SRC (set),0);
>> +
>> + bool copy_needed
>> + = (REGNO (SET_DEST (set)) != REGNO (XEXP (SET_SRC (set), 0)));
>
> Maybe use @orig_src here, rather than duplicating XEXP (SET_SRC (set),0)
>
>> + if (!copy_needed && ext_dst_mode != GET_MODE (orig_src)
>
> The bailing out for copy_needed needs extra commentary, why ?
>
>> + && FUNCTION_ARG_REGNO_P (REGNO (orig_src))
>> + && !abi_extension_candidate_return_reg_p (insn, REGNO (orig_src)))
>> + return true;
>> +
>> + return false;
>
> Consider this bike-shed but I would arrange this code differently. The main
> case here is check for function args and then the not so imp reasons
>
> + rtx orig_src = XEXP (src, 0);
> +
> + if (!FUNCTION_ARG_REGNO_P (REGNO (orig_src))
> + || abi_extension_candidate_return_reg_p (insn, REGNO (orig_src)))
> + return false;
> +
> + /* commentary as to why .... */
> + if (dst_mode == GET_MODE (orig_src))
> + return false;
>
> - bool copy_needed
> - = (REGNO (SET_DEST (set)) != REGNO (XEXP (SET_SRC (set), 0)));
> + /* copy needed ..... */
> + if (REGNO (SET_DEST (set)) != REGNO (orig_src))
> + return false;
> +
> + return true;
>
>> +/* Return TRUE if the candidate insn is zero extend and regno is
>> + an argument registers. */
>> +
>> +static bool
>> +abi_extension_candidate_argno_p (rtx_code code, int regno)
>> +{
>> + if (code != ZERO_EXTEND)
>> + return false;
>
> ABI assumption still.
>
>> +
>> + if (FUNCTION_ARG_REGNO_P (regno))
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> +/* Return TRUE if the candidate insn doesn't have defs and have
>> + * uses without RTX_BIN_ARITH/RTX_COMM_ARITH/RTX_UNARY rtx class. */
>> +
>> +static bool
>> +abi_handle_regs_without_defs_p (rtx_insn *insn)
>> +{
>> + if (side_effects_p (PATTERN (insn)))
>> + return false;
>> +
>> + struct df_link *uses = get_uses (insn, SET_DEST (PATTERN (insn)));
>> +
>> + if (!uses)
>> + return false;
>> +
>> + for (df_link *use = uses; use; use = use->next)
>> + {
>> + if (!use->ref)
>> + return false;
>> +
>> + if (BLOCK_FOR_INSN (insn) != BLOCK_FOR_INSN (DF_REF_INSN (use->ref)))
>> + return false;
>> +
>> + rtx_insn *use_insn = DF_REF_INSN (use->ref);
>> +
>> + if (GET_CODE (PATTERN (use_insn)) == SET)
>> + {
>> + rtx_code code = GET_CODE (SET_SRC (PATTERN (use_insn)));
>> +
>> + if (GET_RTX_CLASS (code) == RTX_BIN_ARITH
>> + || GET_RTX_CLASS (code) == RTX_COMM_ARITH
>> + || GET_RTX_CLASS (code) == RTX_UNARY)
>> + return false;
>> + }
>> + }
>> + return true;
>> +}
>> +
>> /* This function goes through all reaching defs of the source
>> of the candidate for elimination (CAND) and tries to combine
>> the extension with the definition instruction. The changes
>> @@ -770,6 +883,11 @@ combine_reaching_defs (ext_cand *cand, const_rtx
>> set_pat, ext_state *state)
>> state->defs_list.truncate (0);
>> state->copies_list.truncate (0);
>> + rtx orig_src = XEXP (SET_SRC (cand->expr),0);
>> +
>> + if (abi_extension_candidate_p (cand->insn)
>> + && (!get_defs (cand->insn, orig_src, NULL)))
>> + return abi_handle_regs_without_defs_p (cand->insn);
>> outcome = make_defs_and_copies_lists (cand->insn, set_pat, state);
>> @@ -1036,6 +1154,15 @@ combine_reaching_defs (ext_cand *cand, const_rtx
>> set_pat, ext_state *state)
>> }
>> }
>> + rtx insn_set = single_set (cand->insn);
>> +
>> + machine_mode mode = (GET_MODE (XEXP (SET_SRC (insn_set), 0)));
>> +
>> + bool promote_p = abi_target_promote_function_mode (mode);
>> +
>> + if (promote_p)
>> + return true;
>> +
>> if (merge_successful)
>> {
>> /* Commit the changes here if possible
>> @@ -1112,12 +1239,20 @@ add_removable_extension (const_rtx expr, rtx_insn
>> *insn,
>> rtx reg = XEXP (src, 0);
>> struct df_link *defs, *def;
>> ext_cand *cand;
>> + defs = get_defs (insn, reg, NULL);
>> /* Zero-extension of an undefined value is partly defined (it's
>> completely undefined for sign-extension, though). So if there exists
>> a path from the entry to this zero-extension that leaves this register
>> uninitialized, removing the extension could change the behavior of
>> correct programs. So first, check it is not the case. */
>> + if (!defs && abi_extension_candidate_argno_p (code, REGNO (reg)))
>> + {
>> + ext_cand e = {expr, code, mode, insn};
>> + insn_list->safe_push (e);
>> + return;
>> + }
>> +
> Naively I would expect this change to go in the existing !defs { } block
> below, after the uninitialized case but it seems this is deliberate - you
> could be bypassing the uninitialized data case ... (see below as well)
>
>> if (code == ZERO_EXTEND && !bitmap_bit_p (init_regs, REGNO (reg)))
>> {
>> if (dump_file)
>> @@ -1131,7 +1266,6 @@ add_removable_extension (const_rtx expr, rtx_insn
>> *insn,
>> }
>> /* Second, make sure we can get all the reaching definitions. */
>> - defs = get_defs (insn, reg, NULL);
>> if (!defs)
>> {
>> if (dump_file)
>> @@ -1321,7 +1455,8 @@ find_and_remove_re (void)
>> && (REGNO (SET_DEST (set)) != REGNO (XEXP (SET_SRC (set), 0))))
>> {
>> reinsn_copy_list.safe_push (curr_cand->insn);
>> - reinsn_copy_list.safe_push (state.defs_list[0]);
>> + if (state.defs_list.length () != 0)
>> + reinsn_copy_list.safe_push (state.defs_list[0]);
>> }
>> reinsn_del_list.safe_push (curr_cand->insn);
>> state.modified[INSN_UID (curr_cand->insn)].deleted = 1;
>> @@ -1345,6 +1480,10 @@ find_and_remove_re (void)
>> for (unsigned int i = 0; i < reinsn_copy_list.length (); i += 2)
>> {
>> rtx_insn *curr_insn = reinsn_copy_list[i];
>> +
>> + if ((i+1) >= reinsn_copy_list.length ())
>> + continue;
>> +
>> rtx_insn *def_insn = reinsn_copy_list[i + 1];
>> /* Use the mode of the destination of the defining insn
>> diff --git a/gcc/testsuite/g++.target/powerpc/zext-elim-3.C
>> b/gcc/testsuite/g++.target/powerpc/zext-elim-3.C
>> new file mode 100644
>> index 00000000000..5a050df06ff
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.target/powerpc/zext-elim-3.C
>> @@ -0,0 +1,13 @@
>> +/* { dg-options "-mcpu=power9 -O2" } */
>> +
>> +void *memset(void *b, int c, unsigned long len)
>> +{
>> + unsigned long i;
>> +
>> + for (i = 0; i < len; i++)
>> + ((unsigned char *)b)[i] = c;
>> +
>> + return b;
>> +}
>
> So I did a simple cc1 build for powerpc on gcc tip w/ and w/o your patch.
> W/o the patch this test generates the rlwinm insn and REE spits out.
>
> | Cannot eliminate extension:
> | (insn 20 18 22 3 (set (reg:SI 4 4)
> | (zero_extend:SI (reg:QI 4 4 [orig:120 c+3 ] [120])))
> "zext-elim-3.c":8:29 7 {zero_extendqisi2}
> | (nil))
> | because it can operate on uninitialized data
>
> With the patch obviously the extension insn goes away and so does the
> diagnostic, but it wonder your abi_extension_candidate_argno_p () check
> before uniinitialized data check is correct/safe ? I've not looked closely
> what the scope of that check is
>
> IOW, is this test case sufficient or do we need a different test which would
> cure a genuine "missing definitiion(s)" bailout of REE ?
>
>> +/* { dg-final { scan-assembler-not "\mrlwinm\M" } } */
>
> Thanks,
> -Vineet
