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Re: How to check if two symbols are from same source unit during WPA ?
- From: Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>
- To: Richard Biener <rguenther at suse dot de>, Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>
- Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Jan Hubicka <hubicka at ucw dot cz>, <nd at arm dot com>
- Date: Thu, 14 Apr 2016 13:22:37 +0100
- Subject: Re: How to check if two symbols are from same source unit during WPA ?
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> What happens in practice? GCC doesn't put functions in random
The data goes into a separate partition AFAIU - it means that all data accesses are as though they are extern references which means there's not necessarily any CSE'ing ability that's available with section anchors.
>> If it's not desired by default could we gate it on an option ?
>> AFIAU, section anchors optimization is important for ARM and AArch64.
> For code size or for performance? I wonder why section anchors cannot
> be "implemented" using some special relocations and thus as linker
For performance (and probably code size too) as you can end up CSE'ing the anchor point. the difference in performance with -flto-partitions=1 is visible on quite a few of the spec2k benchmarks. I don't remember which ones immediately but yeah it makes a difference.