optimize group_norm op forward

[Zjq9409]

PR types

Performance optimization

PR changes

OPs

Describe

优化group_norm前向计算，性能数据如下：

op 配置	竞品耗时	优化前	优化前相比竞品	优化后	优化后相比竞品	加速比
shape:[2,256,38,26] format:NCHW num_groups:32	0.02117	0.04225	差于 (99.57%)	0.01795	优于 (17.43%)	2.35
shape:[2,256,152,104] format:NCHW num_groups:32	0.23219	0.16161	优于 (30.40%)	0.15235	优于 (34.88%)	1.06
shape:[2,256,76,52] format:NCHW num_groups:32	0.07497	0.06083	优于 (18.86%)	0.04633	优于 (39.20%)	1.31
shape:[2,256,25,33] format:NCHW num_groups:32	0.01947	0.03758	差于 (93.01%)	0.01700	优于 (14.87%)	2.21
shape:[2,256,100,132] format:NCHW num_groups:32	0.19650	0.13734	优于 (30.11%)	0.12765	优于 (35.29%)	1.08
shape:[2,256,50,66] format:NCHW num_groups:32	0.06498	0.05723	优于 (11.93%)	0.04360	优于 (34.01%)	1.31
shape:[2,256,10,11] format:NCHW num_groups:32	0.01237	0.01240	打平 (0.24%)	0.01210	优于 (5.76%)	1.02
shape:[2,256,13,13] format:NCHW num_groups:32	0.01302	0.01431	差于 (9.91%)	0.01216	优于 (10.72%)	1.18
shape:[2,256,144,128] format:NCHW num_groups:32	0.26362	0.18560	优于 (29.60%)	0.17858	优于 (32.90%)	1.04
shape:[2,256,74,68] format:NCHW num_groups:32	0.09320	0.06974	优于 (25.17%)	0.05837	优于 (38.22%)	1.19
shape:[2,128,25,42] format:NCHW num_groups:32	0.01671	0.02433	差于 (45.60%)	0.01533	优于 (11.49%)	1.59
shape:[2,128,70,76] format:NCHW num_groups:32	0.05383	0.04167	优于 (22.59%)	0.03378	优于 (37.98%)	1.23
shape:[2,256,280,304] format:NCHW num_groups:32	1.15604	0.78128	优于 (32.42%)	0.74375	优于 (34.79%)	1.05
shape:[2,256,304,232] format:NCHW num_groups:32	0.96063	0.64988	优于 (32.35%)	0.61566	优于 (38.55%)	1.06
shape:[2,128,35,38] format:NCHW num_groups:32	0.01805	0.02479	差于 (37.34%)	0.01577	优于 (15.53%)	1.57
shape:[2,256,272,312] format:NCHW num_groups:32	1.14480	0.79385	优于 (30.66%)	0.75510	优于 (34.66%)	1.05
shape:[2,256,320,312] format:NCHW num_groups:32	1.34865	0.94088	优于 (30.24%)	0.90426	优于 (33.77%)	1.04
shape:[2,256,280,200] format:NCHW num_groups:32	0.76366	0.53387	优于 (30.09%)	0.51111	优于 (34.21%)	1.04
shape:[2,128,140,152] format:NCHW num_groups:32	0.16234	0.11581	优于 (28.66%)	0.11129	优于 (31.72%)	1.04
shape:[2,128,136,156] format:NCHW num_groups:32	0.16323	0.11468	优于 (29.74%)	0.10998	优于 (32.62%)	1.04

[paddle-bot-old]

Thanks for your contribution!
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[ZzSean]

这个变量有必要吗

[Zjq9409]

bid * groups + gid;后续使用了三次，所以定义了一个变量保存，减少后续索引计算量

[ZzSean]

LGTM