[PATCH] D90884: [SmallVector] Add a default small size.

[Sean Silva via Phabricator via llvm-commits]

silvas added a comment.

In D90884#2377537 <https://reviews.llvm.org/D90884#2377537>, @rnk wrote:

> In D90884#2377497 <https://reviews.llvm.org/D90884#2377497>, @mehdi_amini wrote:
>
>> Seems like it'll always have a default payload equivalent of 6 pointers? Maybe you can document this? Also that makes the vector 72B, which isn't cache line aligned, should we make it 64 or 128 instead?
>
> Right, the header is usually two pointers big (64-bit), so 3x the header is 72. Maybe keeping the size under 128 makes more sense.

The current logic would make sizeof(SmallVector) < 3 * 16B, which is 48B. The current logic is a heuristic like "if you're willing to put the header on the stack, you're willing to put 3 headers on the stack" (not 3 *additional* headers; sorry for injecting the off-by-one into this discussion)


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https://reviews.llvm.org/D90884