[PATCH] D59797: [COFF] Reorder fields in Chunk and SectionChunk to reduce their size

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added inline comments.


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Comment at: lld/COFF/Chunks.cpp:47
 
+namespace {
+// This class exists just for the purpose of calculating the expected size of
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rnk wrote:
> ruiu wrote:
> > rnk wrote:
> > > ruiu wrote:
> > > > This might be useful but at the same time it looks a bit overly cautious? Perhaps the symbol size is more important but we don't have something like this for them, for example.
> > > Well, we don't have checks for symbol size yet. :)
> > > 
> > > Given that we don't have performance monitoring, I really want people to think hard before they casually add another field to SectionChunk. I wouldn't insist on it if we did, but these types of static_asserts have proven useful in LLVM for preventing size creep.
> > Then maybe reiterating everything again, how about checking directly with a number like `static_assert(sizeof(Chunk) == 48)`? This should suffice to prevent making the struct larger by accident.
> It would be wrong for 32-bit. Rather than trying to express it as math on sizeof(void*), I think the struct makes it clearer. And it helps document hidden members like vptr.
Yeah, but it still feels weird to me to repeat all the members again in a different file just for the purpose of assertion. For 32-bit, we can just set the upper bound like `static_assert(sizeof(Chunk) <= 48)` where 48 is the size of the struct in 64-bit.


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  https://reviews.llvm.org/D59797/new/

https://reviews.llvm.org/D59797