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Date: Mon, 18 Nov 2013 21:57:00 -0000
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Subject: Re: [PATCH] Support addsub/subadd as non-isomorphic operations for SLP vectorizer.
From: Uros Bizjak <ubizjak@gmail.com>
To: Cong Hou <congh@google.com>
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>, Richard Biener <rguenther@suse.de>
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On Mon, Nov 18, 2013 at 9:15 PM, Cong Hou <congh@google.com> wrote:

>>> This patch adds the support to two non-isomorphic operations addsub
>>> and subadd for SLP vectorizer. More non-isomorphic operations can be
>>> added later, but the limitation is that operations on even/odd
>>> elements should still be isomorphic. Once such an operation is
>>> detected, the code of the operation used in vectorized code is stored
>>> and later will be used during statement transformation. Two new GIMPLE
>>> opeartions VEC_ADDSUB_EXPR and VEC_SUBADD_EXPR are defined. And also
>>> new optabs for them. They are also documented.
>>>
>>> The target supports for SSE/SSE2/SSE3/AVX are added for those two new
>>> operations on floating points. SSE3/AVX provides ADDSUBPD and ADDSUBPS
>>> instructions. For SSE/SSE2, those two operations are emulated using
>>> two instructions (selectively negate then add).
>>
>> +(define_expand "vec_subadd_v4sf3"
>> +  [(set (match_operand:V4SF 0 "register_operand")
>> + (unspec:V4SF
>> +  [(match_operand:V4SF 1 "register_operand")
>> +   (match_operand:V4SF 2 "nonimmediate_operand")] UNSPEC_SUBADD))]
>> +  "TARGET_SSE"
>> +{
>> +  if (TARGET_SSE3)
>> +    emit_insn (gen_sse3_addsubv4sf3 (operands[0], operands[1], operands[2]));
>> +  else
>> +    ix86_sse_expand_fp_addsub_operator (true, V4SFmode, operands);
>> +  DONE;
>> +})
>>
>> Make the expander pattern look like correspondig sse3 insn and:
>> ...
>> {
>>   if (!TARGET_SSE3)
>>     {
>>       ix86_sse_expand_fp_...();
>>       DONE;
>>     }
>> }
>>
>
> You mean I should write two expanders for SSE and SSE3 respectively?

No, please use the same approach as you did for abs<mode>2 expander.
For !TARGET_SSE3, call the helper function (ix86_sse_expand...),
otherwise expand through pattern. Also, it looks to me that you should
partially expand in the pattern before calling helper function, mainly
to avoid a bunch of "if (...)" at the beginning of the helper
function.

Uros.