[llvm-dev] AttrBuilder API change

[Serge Guelton via llvm-dev]

Hi folks,

the AttrBuilder class has been showing off a lot on performance report,
impacting compile time in a negative and unnecessery way. Several commits [1] by
Nikita Popov already improved the situation by avoid unnecesseray calls to this
builder, and more recenly, the AttributeMask class got introduced [2] as a way to
split the logic between adding and removing attributes.

The final step [3] (that sometimes give a 1% performance increase! [4]) avoid
using an std::map of SmallString to store target dependent attributes, and uses
a SmallVector of Attribute instead.

This implies changing all AttrBuilder constructors to take an LLVMContext as
parameter. Given how widely used this class is, I thought I'd advertise the
change here and let it mature a few extra days before it gets merged!

In [3], rnk is suggesting I'd land a temporary commit that introduces extra
constructors that accept an extra LLVM Context just to ease the transition.
Would that be useful to someone here?

[1] eg 6e30cb7673df293fd294acef7eadca8050b5a71e
[2] 9290ccc3c1a17a7874de020656db38183a20f6b0
[3] https://reviews.llvm.org/D116599
[4] https://llvm-compile-time-tracker.com/compare.php?from=5de322295f4ade692dc4f1823ae4450ad3c48af2&to=05bc480bf641a9e3b466619af43a2d123ee3f71d&stat=instructions