[PATCH][rs6000] avoid using unaligned vsx or lxvd2x/stxvd2x for memcpy/memmove inline expansion

[Aaron Sawdey]

The patch for this was committed to trunk as 267562 (see below). Is this also ok for backport to 8?

Thanks,
   Aaron

On 12/20/18 5:44 PM, Segher Boessenkool wrote:
> On Thu, Dec 20, 2018 at 05:34:54PM -0600, Aaron Sawdey wrote:
>> On 12/20/18 3:51 AM, Segher Boessenkool wrote:
>>> On Wed, Dec 19, 2018 at 01:53:05PM -0600, Aaron Sawdey wrote:
>>>> Because of POWER9 dd2.1 issues with certain unaligned vsx instructions
>>>> to cache inhibited memory, here is a patch that keeps memmove (and memcpy)
>>>> inline expansion from doing unaligned vector or using vector load/store
>>>> other than lvx/stvx. More description of the issue is here:
>>>>
>>>> https://patchwork.ozlabs.org/patch/814059/
>>>>
>>>> OK for trunk if bootstrap/regtest ok?
>>>
>>> Okay, but see below.
>>>
>> [snip]
>>>
>>> This is extraordinarily clumsy :-)  Maybe something like:
>>>
>>> static rtx
>>> gen_lvx_v4si_move (rtx dest, rtx src)
>>> {
>>>   gcc_assert (!(MEM_P (dest) && MEM_P (src));
>>>   gcc_assert (GET_MODE (dest) == V4SImode && GET_MODE (src) == V4SImode);
>>>   if (MEM_P (dest))
>>>     return gen_altivec_stvx_v4si_internal (dest, src);
>>>   else if (MEM_P (src))
>>>     return gen_altivec_lvx_v4si_internal (dest, src);
>>>   else
>>>     gcc_unreachable ();
>>> }
>>>
>>> (Or do you allow VOIDmode for src as well?)  Anyway, at least get rid of
>>> the useless extra variable.
>>
>> I think this should be better:
> 
> The gcc_unreachable at the end catches the non-mem to non-mem case.
> 
>> static rtx
>> gen_lvx_v4si_move (rtx dest, rtx src)
>> {
>>   gcc_assert ((MEM_P (dest) && !MEM_P (src)) || (MEM_P (src) && !MEM_P(dest)));
> 
> But if you prefer this, how about
> 
> {
>   gcc_assert (MEM_P (dest) ^ MEM_P (src));
>   gcc_assert (GET_MODE (dest) == V4SImode && GET_MODE (src) == V4SImode);
> 
>   if (MEM_P (dest))
>     return gen_altivec_stvx_v4si_internal (dest, src);
>   else
>     return gen_altivec_lvx_v4si_internal (dest, src);
> }
> 
> :-)
> 
> 
> Segher
> 

2019-01-03  Aaron Sawdey  <acsawdey@linux.ibm.com>

        * config/rs6000/rs6000-string.c (expand_block_move): Don't use
        unaligned vsx and avoid lxvd2x/stxvd2x.
        (gen_lvx_v4si_move): New function.


Index: gcc/config/rs6000/rs6000-string.c
===================================================================
--- gcc/config/rs6000/rs6000-string.c	(revision 267299)
+++ gcc/config/rs6000/rs6000-string.c	(working copy)
@@ -2669,6 +2669,25 @@
   return true;
 }

+/* Generate loads and stores for a move of v4si mode using lvx/stvx.
+   This uses altivec_{l,st}vx_<mode>_internal which use unspecs to
+   keep combine from changing what instruction gets used.
+
+   DEST is the destination for the data.
+   SRC is the source of the data for the move.  */
+
+static rtx
+gen_lvx_v4si_move (rtx dest, rtx src)
+{
+  gcc_assert (MEM_P (dest) ^ MEM_P (src));
+  gcc_assert (GET_MODE (dest) == V4SImode && GET_MODE (src) == V4SImode);
+
+  if (MEM_P (dest))
+    return gen_altivec_stvx_v4si_internal (dest, src);
+  else
+    return gen_altivec_lvx_v4si_internal (dest, src);
+}
+
 /* Expand a block move operation, and return 1 if successful.  Return 0
    if we should let the compiler generate normal code.

@@ -2721,11 +2740,11 @@

       /* Altivec first, since it will be faster than a string move
 	 when it applies, and usually not significantly larger.  */
-      if (TARGET_ALTIVEC && bytes >= 16 && (TARGET_EFFICIENT_UNALIGNED_VSX || align >= 128))
+      if (TARGET_ALTIVEC && bytes >= 16 && align >= 128)
 	{
 	  move_bytes = 16;
 	  mode = V4SImode;
-	  gen_func.mov = gen_movv4si;
+	  gen_func.mov = gen_lvx_v4si_move;
 	}
       else if (bytes >= 8 && TARGET_POWERPC64
 	       && (align >= 64 || !STRICT_ALIGNMENT))



-- 
Aaron Sawdey, Ph.D.  acsawdey@linux.vnet.ibm.com
050-2/C113  (507) 253-7520 home: 507/263-0782
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