This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: ARM peephole2 from 2003 never merged, still valid
On 6/2/19 6:28 AM, Segher Boessenkool wrote:
> On Sat, Jun 01, 2019 at 11:41:30PM +0000, Fredrik Hederstierna wrote:
>> +(define_peephole2
>> + [(set (match_operand:SI 0 "arm_general_register_operand" "")
>> + (match_operand:SI 1 "arm_general_register_operand" ""))
>> + (set (reg:CC CC_REGNUM)
>> + (compare:CC (match_dup 0) (const_int 0)))]
>> + "TARGET_ARM"
>> + [(parallel [(set (reg:CC CC_REGNUM) (compare:CC (match_dup 1) (const_int 0)))
>> + (set (match_dup 0) (match_dup 1))])]
>> + ""
>> +)
>
> Hi Fredrik,
>
> Do you have a testcase for this? I wonder if it would be better handled
> during combine, and what that then tried; or perhaps these opportunities
> are created later, making a peephole a more attractive solution.
We have two independent insns with no output/true dependency between
them. So there's really not anything for combine to do here.
What is more interesting to me is whether or not this could be handled
by compare-elim and a define_insn rather than a define_peephole2. THe
existing pattern and the new one both seem well suited for compare-elim.
I do think a testcase is warranted here. Fredrik, if you could reduce
one from CSiBE that might be appropriate.
jeff