OK to backport to GCC13 (it applies cleanly and regress/bootstrap passes)?
Cheers,
Wilco
On 29/11/2023 18:09, Richard Sandiford wrote:
> Wilco Dijkstra <wilco.dijks...@arm.com> writes:
>> v2: Use UINTVAL, rename max_mops_size.
>>
>> The cpymemdi/setmemdi implementation doesn't fully support strict alignment.
>> Block the expansion if the alignment is less than 16 with STRICT_ALIGNMENT.
>> Clean up the condition when to use MOPS.
>>
>> Passes regress/bootstrap, OK for commit?
>>
>> gcc/ChangeLog/
>> PR target/103100
>> * config/aarch64/aarch64.md (cpymemdi): Remove pattern condition.
>> (setmemdi): Likewise.
>> * config/aarch64/aarch64.cc (aarch64_expand_cpymem): Support
>> strict-align. Cleanup condition for using MOPS.
>> (aarch64_expand_setmem): Likewise.
>>
>> ---
>>
>> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
>> index
>> dd6874d13a75f20d10a244578afc355b25c73da2..8a12894d6b80de1031d6e7d02dca680c57bce136
>> 100644
>> --- a/gcc/config/aarch64/aarch64.cc
>> +++ b/gcc/config/aarch64/aarch64.cc
>> @@ -25261,27 +25261,23 @@ aarch64_expand_cpymem (rtx *operands)
>> int mode_bits;
>> rtx dst = operands[0];
>> rtx src = operands[1];
>> + unsigned align = UINTVAL (operands[3]);
>> rtx base;
>> machine_mode cur_mode = BLKmode;
>> + bool size_p = optimize_function_for_size_p (cfun);
>>
>> - /* Variable-sized memcpy can go through the MOPS expansion if available.
>> */
>> - if (!CONST_INT_P (operands[2]))
>> + /* Variable-sized or strict-align copies may use the MOPS expansion. */
>> + if (!CONST_INT_P (operands[2]) || (STRICT_ALIGNMENT && align < 16))
>> return aarch64_expand_cpymem_mops (operands);
>>
>> - unsigned HOST_WIDE_INT size = INTVAL (operands[2]);
>> -
>> - /* Try to inline up to 256 bytes or use the MOPS threshold if available.
>> */
>> - unsigned HOST_WIDE_INT max_copy_size
>> - = TARGET_MOPS ? aarch64_mops_memcpy_size_threshold : 256;
>> + unsigned HOST_WIDE_INT size = UINTVAL (operands[2]);
>>
>> - bool size_p = optimize_function_for_size_p (cfun);
>> + /* Try to inline up to 256 bytes. */
>> + unsigned max_copy_size = 256;
>> + unsigned mops_threshold = aarch64_mops_memcpy_size_threshold;
>>
>> - /* Large constant-sized cpymem should go through MOPS when possible.
>> - It should be a win even for size optimization in the general case.
>> - For speed optimization the choice between MOPS and the SIMD sequence
>> - depends on the size of the copy, rather than number of instructions,
>> - alignment etc. */
>> - if (size > max_copy_size)
>> + /* Large copies use MOPS when available or a library call. */
>> + if (size > max_copy_size || (TARGET_MOPS && size > mops_threshold))
>> return aarch64_expand_cpymem_mops (operands);
>
> It feels a little unintuitive to be calling aarch64_expand_cpymem_mops
> for !TARGET_MOPS, but that's pre-existing, and I can see there are
> arguments both ways.
>
> Although !TARGET_SIMD is a niche interest on current trunk, it becomes
> important for streaming-compatible mode. So we might want to look
> again at the different handling of !TARGET_SIMD in this function (where
> we lower the copy size but not the threshold) and aarch64_expand_setmem
> (where we bail out early). That's not something for this patch though,
> just mentioning it.
>
> The patch is OK with me, but please give Richard E a day to object.
This is fine by me.
R.
>
> Thanks,
> Richard
>
>>
>> int copy_bits = 256;
>> @@ -25445,12 +25441,13 @@ aarch64_expand_setmem (rtx *operands)
>> unsigned HOST_WIDE_INT len;
>> rtx dst = operands[0];
>> rtx val = operands[2], src;
>> + unsigned align = UINTVAL (operands[3]);
>> rtx base;
>> machine_mode cur_mode = BLKmode, next_mode;
>>
>> - /* If we don't have SIMD registers or the size is variable use the MOPS
>> - inlined sequence if possible. */
>> - if (!CONST_INT_P (operands[1]) || !TARGET_SIMD)
>> + /* Variable-sized or strict-align memset may use the MOPS expansion. */
>> + if (!CONST_INT_P (operands[1]) || !TARGET_SIMD
>> + || (STRICT_ALIGNMENT && align < 16))
>> return aarch64_expand_setmem_mops (operands);
>>
>> bool size_p = optimize_function_for_size_p (cfun);
>> @@ -25458,10 +25455,13 @@ aarch64_expand_setmem (rtx *operands)
>> /* Default the maximum to 256-bytes when considering only libcall vs
>> SIMD broadcast sequence. */
>> unsigned max_set_size = 256;
>> + unsigned mops_threshold = aarch64_mops_memset_size_threshold;
>>
>> - len = INTVAL (operands[1]);
>> - if (len > max_set_size && !TARGET_MOPS)
>> - return false;
>> + len = UINTVAL (operands[1]);
>> +
>> + /* Large memset uses MOPS when available or a library call. */
>> + if (len > max_set_size || (TARGET_MOPS && len > mops_threshold))
>> + return aarch64_expand_setmem_mops (operands);
>>
>> int cst_val = !!(CONST_INT_P (val) && (INTVAL (val) != 0));
>> /* The MOPS sequence takes:
>> @@ -25474,12 +25474,6 @@ aarch64_expand_setmem (rtx *operands)
>> the arguments + 1 for the call. */
>> unsigned libcall_cost = 4;
>>
>> - /* Upper bound check. For large constant-sized setmem use the MOPS
>> sequence
>> - when available. */
>> - if (TARGET_MOPS
>> - && len >= (unsigned HOST_WIDE_INT) aarch64_mops_memset_size_threshold)
>> - return aarch64_expand_setmem_mops (operands);
>> -
>> /* Attempt a sequence with a vector broadcast followed by stores.
>> Count the number of operations involved to see if it's worth it
>> against the alternatives. A simple counter simd_ops on the
>> @@ -25521,10 +25515,8 @@ aarch64_expand_setmem (rtx *operands)
>> simd_ops++;
>> n -= mode_bits;
>>
>> - /* Do certain trailing copies as overlapping if it's going to be
>> - cheaper. i.e. less instructions to do so. For instance doing a 15
>> - byte copy it's more efficient to do two overlapping 8 byte copies
>> than
>> - 8 + 4 + 2 + 1. Only do this when -mstrict-align is not supplied.
>> */
>> + /* Emit trailing writes using overlapping unaligned accesses
>> + (when !STRICT_ALIGNMENT) - this is smaller and faster. */
>> if (n > 0 && n < copy_limit / 2 && !STRICT_ALIGNMENT)
>> {
>> next_mode = smallest_mode_for_size (n, MODE_INT);
>> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
>> index
>> 6d0f072a9dd6d094e8764a513222a9129d8296fa..96508a2580876d1fdbdfa6c67d1a3d02608c1d24
>> 100644
>> --- a/gcc/config/aarch64/aarch64.md
>> +++ b/gcc/config/aarch64/aarch64.md
>> @@ -1627,7 +1627,7 @@ (define_expand "cpymemdi"
>> (match_operand:BLK 1 "memory_operand")
>> (match_operand:DI 2 "general_operand")
>> (match_operand:DI 3 "immediate_operand")]
>> - "!STRICT_ALIGNMENT || TARGET_MOPS"
>> + ""
>> {
>> if (aarch64_expand_cpymem (operands))
>> DONE;
>> @@ -1724,7 +1724,7 @@ (define_expand "setmemdi"
>> (match_operand:QI 2 "nonmemory_operand")) ;; Value
>> (use (match_operand:DI 1 "general_operand")) ;; Length
>> (match_operand 3 "immediate_operand")] ;; Align
>> - "TARGET_SIMD || TARGET_MOPS"
>> + ""
>> {
>> if (aarch64_expand_setmem (operands))
>> DONE;
