Re: [PATCH]rs6000: Load high and low part of 64bit constant independently

[Jiufu Guo <guojiufu@linux.ibm.com>]

Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

> Hi Kewen,
>
> Thanks for your review on this patch!
>
> "Kewen.Lin" <linkw@linux.ibm.com> writes:
>
>> Hi Jeff,
>>
>> Sorry for the late review.
>>
>> on 2022/9/15 16:30, Jiufu Guo wrote:
>>> Hi,
>>> 
>>> For a complicate 64bit constant, blow is one instruction-sequence to
>>> build:
>>> 	lis 9,0x800a
>>> 	ori 9,9,0xabcd
>>> 	sldi 9,9,32
>>> 	oris 9,9,0xc167
>>> 	ori 9,9,0xfa16
>>> 
>>> while we can also use below sequence to build:
>>> 	lis 9,0xc167
>>> 	lis 10,0x800a
>>> 	ori 9,9,0xfa16
>>> 	ori 10,10,0xabcd
>>> 	rldimi 9,10,32,0
>>> This sequence is using 2 registers to build high and low part firstly,
>>> and then merge them.
>>> In parallel aspect, this sequence would be faster. (Ofcause, using 1 more
>>> register with potential register pressure).
>>> 
>>> Bootstrap and regtest pass on ppc64le.
>>> Is this ok for trunk?
>>> 
>>> 
>>> BR,
>>> Jeff(Jiufu)
>>> 
>>> 
>>> gcc/ChangeLog:
>>> 
>>> 	* config/rs6000/rs6000.cc (rs6000_emit_set_long_const): Update 64bit
>>> 	constant build.
>>> 
>>> gcc/testsuite/ChangeLog:
>>> 
>>> 	* gcc.target/powerpc/parall_5insn_const.c: New test.
>>> 
>>> ---
cut...
> @@ -0,1 +1,27 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -mdejagnu-cpu=power8  -save-temps" } */
maybe, I could use power7.  Any comments?
> +/* { dg-require-effective-target has_arch_ppc64 } */
> +
> +/* { dg-final { scan-assembler-times {\mlis\M} 4 } } */
> +/* { dg-final { scan-assembler-times {\mori\M} 4 } } */
> +/* { dg-final { scan-assembler-times {\mrldimi\M} 2 } } */
> +
> +void __attribute__ ((noinline)) foo (unsigned long long *a)
> +{
> +  /* 2 lis + 2 ori + 1 rldimi for each constant.  */
> +  *a++ = 0x800aabcdc167fa16ULL;
> +  *a++ = 0x7543a876867f616ULL;
> +}
> +
> +long long A[] = {0x800aabcdc167fa16ULL, 0x7543a876867f616ULL};
> +int
> +main ()
> +{
> +  long long res[2];
> +
> +  foo (res);
> +  if (__builtin_memcmp (res, A, sizeof (res)) != 0)
> +    __builtin_abort ();
> +
> +  return 0;
> +}