[PATCH] D27960: Use exact vector capacities to store DWARF line tables

[Mehdi AMINI via Phabricator via llvm-commits]

mehdi_amini added a comment.

In https://reviews.llvm.org/D27960#627263, @sque wrote:

> mehdi_amini asked: "Isn't there a way to `reserve()` appropriately initially?"
>
> Not trivially. Look at the while loop that precedes the new code. It looks through the line table but doesn't know beforehand how many Rows there are.


I saw that, but I was more wondering if there isn't another way in the Dwarf to get the information (I don't know if this number could be encoded somehow separately).

> One possible optimization is to first have a dry-run that counts the number of Rows, reserves memory for them, and then runs through again to create the Rows.

Right, but it depends how fast is it to perform this dry-run, especially compared to cost of a little bit of wasted memory.
I mean the maximum waste here is always < 1 page of memory right?


https://reviews.llvm.org/D27960