"BOLT" post-link optimizer gives 15% speed boost to Clang

[welkam]

On Wednesday, 24 October 2018 at 01:57:38 UTC, Walter Bright 
wrote:
> Yup, it's reinvention of the same thing.

The authors never claimed that they invented anything. What they 
claim is that doing reordering after linking has benefits that 
compiler cant easily do. Bolt improves performance on top of 
PGO+LTO by:

1. Using more accurate profile data from intel`s last branch 
record(LBR)
2. Inlining function some times changes hotness of code blocks 
based on where it was inlined so doing profiling after inlining 
gives better decision making for Bolt.

The negative of Bolt`s approach is that is limited on what 
allowed transformations it can do so people should use 
PGO+LTO+Bolt for maximum performance. Second negative is that it 
works with ELF format so windows users wont benefit from it.