ping^^: [PATCH] rs6000: Enable const_anchor for 'addi'

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

Gentle ping...

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

> Gentle ping...
>
> Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
>
>> Hi,
>>
>> I'm thinking that we may enable this patch for stage1, so ping it.
>> https://gcc.gnu.org/pipermail/gcc-patches/2022-October/603530.html
>>
>> BR,
>> Jeff (Jiufu)
>>
>> Jiufu Guo <guojiufu@linux.ibm.com> writes:
>>
>>> Hi,
>>>
>>> There is a functionality as const_anchor in cse.cc.  This const_anchor
>>> supports to generate new constants through adding small gap/offsets to
>>> existing constant.  For example:
>>>
>>> void __attribute__ ((noinline)) foo (long long *a)
>>> {
>>>   *a++ = 0x2351847027482577LL;
>>>   *a++ = 0x2351847027482578LL;
>>> }
>>> The second constant (0x2351847027482578LL) can be compated by adding '1'
>>> to the first constant (0x2351847027482577LL).
>>> This is profitable if more than one instructions are need to build the
>>> second constant.
>>>
>>> * For rs6000, we can enable this functionality, as the instruction
>>> 'addi' is just for this when gap is smaller than 0x8000.
>>>
>>> * Besides enabling TARGET_CONST_ANCHOR on rs6000, this patch also fixed
>>> one issue. The issue is:
>>> "gcc_assert (SCALAR_INT_MODE_P (mode))" is an requirement for function
>>> "try_const_anchors". 
>>>
>>> * One potential side effect of this patch:
>>> Comparing with
>>> "r101=0x2351847027482577LL
>>> ...
>>> r201=0x2351847027482578LL"
>>> The new r201 will be "r201=r101+1", and then r101 will live longer,
>>> and would increase pressure when allocating registers.
>>> But I feel, this would be acceptable for this const_anchor feature.
>>>
>>> * With this patch, I checked the performance change on SPEC2017, while,
>>> and the performance is not aggressive, since this functionality is not
>>> hit on any hot path. There are runtime wavings/noise(e.g. on
>>> povray_r/xalancbmk_r/xz_r), that are not caused by the patch.
>>>
>>> With this patch, I also checked the changes in object files (from
>>> GCC bootstrap and SPEC), the significant changes are the improvement
>>> that: "addi" vs. "2 or more insns: lis+or.."; it also exposes some
>>> other optimizations opportunities: like combine/jump2. While the
>>> code to store/load one more register is also occurring in few cases,
>>> but it does not impact overall performance.
>>>
>>> * To refine this patch, some history discussions are referenced:
>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33699
>>> https://gcc.gnu.org/pipermail/gcc-patches/2009-April/260421.html
>>> https://gcc.gnu.org/pipermail/gcc-patches/2021-March/566744.html
>>>
>>>
>>> Bootstrap and regtest pass on ppc64 and ppc64le for this patch.
>>> Is this ok for trunk?
>>>
>>>
>>> BR,
>>> Jeff (Jiufu)
>>>
>>> gcc/ChangeLog:
>>>
>>> 	* config/rs6000/rs6000.cc (TARGET_CONST_ANCHOR): New define.
>>> 	* cse.cc (cse_insn): Add guard condition.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> 	* gcc.target/powerpc/const_anchors.c: New test.
>>> 	* gcc.target/powerpc/try_const_anchors_ice.c: New test.
>>>
>>> ---
>>>  gcc/config/rs6000/rs6000.cc                   |  4 ++++
>>>  gcc/cse.cc                                    |  3 ++-
>>>  .../gcc.target/powerpc/const_anchors.c        | 20 +++++++++++++++++++
>>>  .../powerpc/try_const_anchors_ice.c           | 16 +++++++++++++++
>>>  4 files changed, 42 insertions(+), 1 deletion(-)
>>>  create mode 100644 gcc/testsuite/gcc.target/powerpc/const_anchors.c
>>>  create mode 100644 gcc/testsuite/gcc.target/powerpc/try_const_anchors_ice.c
>>>
>>> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
>>> index d2743f7bce6..80cded6dec1 100644
>>> --- a/gcc/config/rs6000/rs6000.cc
>>> +++ b/gcc/config/rs6000/rs6000.cc
>>> @@ -1760,6 +1760,10 @@ static const struct attribute_spec rs6000_attribute_table[] =
>>>  
>>>  #undef TARGET_UPDATE_IPA_FN_TARGET_INFO
>>>  #define TARGET_UPDATE_IPA_FN_TARGET_INFO rs6000_update_ipa_fn_target_info
>>> +
>>> +#undef TARGET_CONST_ANCHOR
>>> +#define TARGET_CONST_ANCHOR 0x8000
>>> +
>>>  \f
>>>  
>>>  /* Processor table.  */
>>> diff --git a/gcc/cse.cc b/gcc/cse.cc
>>> index b13afd4ba72..56542b91c1e 100644
>>> --- a/gcc/cse.cc
>>> +++ b/gcc/cse.cc
>>> @@ -5005,7 +5005,8 @@ cse_insn (rtx_insn *insn)
>>>        if (targetm.const_anchor
>>>  	  && !src_related
>>>  	  && src_const
>>> -	  && GET_CODE (src_const) == CONST_INT)
>>> +	  && GET_CODE (src_const) == CONST_INT
>>> +	  && SCALAR_INT_MODE_P (mode))
>>>  	{
>>>  	  src_related = try_const_anchors (src_const, mode);
>>>  	  src_related_is_const_anchor = src_related != NULL_RTX;
>>> diff --git a/gcc/testsuite/gcc.target/powerpc/const_anchors.c b/gcc/testsuite/gcc.target/powerpc/const_anchors.c
>>> new file mode 100644
>>> index 00000000000..39958ff9765
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.target/powerpc/const_anchors.c
>>> @@ -0,0 +1,20 @@
>>> +/* { dg-do compile { target has_arch_ppc64 } } */
>>> +/* { dg-options "-O2" } */
>>> +
>>> +#define C1 0x2351847027482577ULL
>>> +#define C2 0x2351847027482578ULL
>>> +
>>> +void __attribute__ ((noinline)) foo (long long *a)
>>> +{
>>> +  *a++ = C1;
>>> +  *a++ = C2;
>>> +}
>>> +
>>> +void __attribute__ ((noinline)) foo1 (long long *a, long long b)
>>> +{
>>> +  *a++ = C1;
>>> +  if (b)
>>> +    *a++ = C2;
>>> +}
>>> +
>>> +/* { dg-final { scan-assembler-times {\maddi\M} 2 } } */
>>> diff --git a/gcc/testsuite/gcc.target/powerpc/try_const_anchors_ice.c b/gcc/testsuite/gcc.target/powerpc/try_const_anchors_ice.c
>>> new file mode 100644
>>> index 00000000000..4c8a892e803
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.target/powerpc/try_const_anchors_ice.c
>>> @@ -0,0 +1,16 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2" } */
>>> +
>>> +/* __builtin_stack_restore could generates {[%1:DI]=0;} in BLK mode,
>>> +   it could case ICE in try_const_anchors which only supports SCALAR_INT.  */
>>> +
>>> +long
>>> +foo (const int val)
>>> +{
>>> +  if (val == (0))
>>> +    return 0;
>>> +  void *p = __builtin_stack_save ();
>>> +  char c = val;
>>> +  __builtin_stack_restore (p);
>>> +  return c;
>>> +}