[PATCH] D98481: [Inliner] Do not inline mutual-recursive functions to avoid exponential size growth.

Mon Mar 15 22:44:03 PDT 2021

hoy added a comment.

In D98481#2628055 <https://reviews.llvm.org/D98481#2628055>, @wenlei wrote:

> In D98481#2628047 <https://reviews.llvm.org/D98481#2628047>, @hoy wrote:
>
>> I got some numbers for SPEC2017 with AutoFDO + LTO. Timing wise no noticeable difference but there is difference in code size for some benchmarks which indicates less inlining with this patch. The difference is pretty big for `perlbench_s` I guess we don't see perf gap because recursive those functions are run a lot more times than the inlined times.
>>
>>   	             After/Before (Code Size)
>>      508.namd_r    	100.00%
>>      510.parest_r  	100.00%
>>      511.povray_r  	97.89%
>>      600.perlbench_s	89.68%
>>      602.gcc_s     	98.79%
>>      605.mcf_s     	100.00%
>>      620.omnetpp_s 	100.00%
>>      623.xalancbmk_s	99.91%
>>      625.x264_s    	100.00%
>>      631.deepsjeng_s	100.00%
>>      638.imagick_s 	99.55%
>>      641.leela_s   	100.00%
>>      644.nab_s     	100.00%
>>      657.xz_s      	100.00%
>
> Do you have numbers on how many times the new check blocks inlining for each (if you move it to be the last check)? The code size number seems to be indicate that the change indeed impacts inlining quite a bit.
>
> When the inline history was introduced in https://reviews.llvm.org/D36188, it was verified that it didn't block any inlining for spec.

Callsite inlining are good counters. For those benchmarks affected, inlined callsites vs non-inlined callsites due to this change are:

                 inlined callsites        recursive callsites    
  511.povray_r        3178                   603
  600.perlbench_s     4577                   2139
  602.gcc_s          46125                   726
  623.xalancbmk_s    15573                   79
  638.imagick_s       7719                   61

Apparently,  `perlbench_s` has a lot less inlining.

Repository:
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  https://reviews.llvm.org/D98481/new/

https://reviews.llvm.org/D98481