Re: [PATCH V3] rs6000: cannot_force_const_mem for HIGH code rtx[PR106460]

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

Hi,

"Kewen.Lin" <linkw@linux.ibm.com> writes:

> Hi Jeff,
>
> on 2022/9/7 15:08, Jiufu Guo via Gcc-patches wrote:
>> Hi,
>> 
>> As the issue in PR106460, a rtx 'high:DI (symbol_ref:DI ("var_48")' is tried
>> to store into constant pool and ICE occur.  But actually, this rtx represents
>> partial address and can not be put into a .rodata section.
>> 
>> This patch updates rs6000_cannot_force_const_mem to return true for rtx(s) with
>> HIGH code, because these rtx(s) indicate part of address and are not ok for
>> constant pool.
>> 
>> Below are some examples:
>> (high:DI (const:DI (plus:DI (symbol_ref:DI ("xx") (const_int 12 [0xc])))))
>> (high:DI (symbol_ref:DI ("var_1")..)))
>> 
>> This patch updated the previous patch, and drafted an test case which ICE
>> without the patch, and assoicated with one PR.
>> https://gcc.gnu.org/pipermail/gcc-patches/2022-July/597712.html
>> This patch also updated the message for previous patch V2.
>> 
>> I would ask help to review this patch one more time.
>> 
>> Bootstrap and regtest pass on ppc64 and ppc64le.
>> Is this ok for trunk.
>> 
>> BR,
>> Jeff(Jiufu)
>> 
>> 	PR target/106460
>> 
>> gcc/ChangeLog:
>> 
>> 	* config/rs6000/rs6000.cc (rs6000_cannot_force_const_mem): Return true
>> 	for HIGH code rtx.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> 	* gcc.target/powerpc/pr106460.c: New test.
>> ---
>>  gcc/config/rs6000/rs6000.cc                 |  7 +++++--
>>  gcc/testsuite/gcc.target/powerpc/pr106460.c | 11 +++++++++++
>>  2 files changed, 16 insertions(+), 2 deletions(-)
>>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr106460.c
>> 
>> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
>> index 2f3146e56f8..04e3a393147 100644
>> --- a/gcc/config/rs6000/rs6000.cc
>> +++ b/gcc/config/rs6000/rs6000.cc
>> @@ -9643,8 +9643,11 @@ rs6000_init_stack_protect_guard (void)
>>  static bool
>>  rs6000_cannot_force_const_mem (machine_mode mode ATTRIBUTE_UNUSED, rtx x)
>>  {
>> -  if (GET_CODE (x) == HIGH
>> -      && GET_CODE (XEXP (x, 0)) == UNSPEC)
>> +  /* If GET_CODE (x) is HIGH, the 'X' represets the high part of a symbol_ref.
>> +     It indicates partial address,  which can not be put into a constant pool.
>> +     e.g.  (high:DI (unspec:DI [(symbol_ref/u:DI ("*.LC0")..)
>> +     (high:DI (symbol_ref:DI ("var")..)).  */
>
> Nit: Maybe it's good to align these two "(high:DI ... ?
OK, thanks! 
>
>> +  if (GET_CODE (x) == HIGH)
>>      return true;
>>  
>>    /* A TLS symbol in the TOC cannot contain a sum.  */
>> diff --git a/gcc/testsuite/gcc.target/powerpc/pr106460.c b/gcc/testsuite/gcc.target/powerpc/pr106460.c
>> new file mode 100644
>> index 00000000000..dfaffcb6e28
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/pr106460.c
>> @@ -0,0 +1,11 @@
>
> Need a power10_ok effective target here.
>
> /* { dg-require-effective-target power10_ok } */
OK, will add this.
>
>> +/* { dg-options "-O1 -mdejagnu-cpu=power10" } */
>
> Nit: As Segher's review on one of my patches, O2 is preferred against O1 if it
> still works for this issue.  The point is to avoid some related optimization
> (routines or passes) to be disabled at O1 one day and this becomes ineffective.
>
Yeap.  While, for this case, the ICE is not reproduciable with -O2.
So, -O1 is used here.

BR,
Jeff (Jiufu)

> BR,
> Kewen