On 20/09/2023 14:50, Wilco Dijkstra wrote:
>
> 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.
Shouldn't this be a separate patch? It's not immediately obvious that this is
a necessary part of this change.
> (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..8f3bfb91c0f4ec43f37fe9289a66092a29a47e4d
> 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 = INTVAL (operands[3]);
This should read the value with UINTVAL. Given the useful range of the
alignment, it should be OK that we're not using unsigned HWI.
> 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);
So what about align=4 and copying, for example, 8 or 12 bytes; wouldn't we want
a sequence of LDR/STR in that case? Doesn't this fall back to MOPS too eagerly?
>
> 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;
> -
> - bool size_p = optimize_function_for_size_p (cfun);
> + /* Try to inline up to 256 bytes. */
> + unsigned max_copy_size = 256;
> + unsigned max_mops_size = aarch64_mops_memcpy_size_threshold;
I find this name slightly confusing. Surely it's min_mops_size (since above
that we want to use MOPS rather than inlined loads/stores). But why not just
use aarch64_mops_memcpy_size_threshold directly in the one place it's used?
>
> - /* 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 > max_mops_size))
> return aarch64_expand_cpymem_mops (operands);
>
> int copy_bits = 256;
> @@ -25445,12 +25441,13 @@ aarch64_expand_setmem (rtx *operands)
Similar comments apply to this code as well.
> unsigned HOST_WIDE_INT len;
> rtx dst = operands[0];
> rtx val = operands[2], src;
> + unsigned align = INTVAL (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)
And here.
> /* Default the maximum to 256-bytes when considering only libcall vs
> SIMD broadcast sequence. */
> unsigned max_set_size = 256;
> + unsigned max_mops_size = aarch64_mops_memset_size_threshold;
>
> len = INTVAL (operands[1]);
> - if (len > max_set_size && !TARGET_MOPS)
> - return false;
> +
> + /* Large memset uses MOPS when available or a library call. */
> + if (len > max_set_size || (TARGET_MOPS && len > max_mops_size))
> + 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;
>
>
Are there any additional tests for this?
R.
