undefined | Better HN

0 pointsndesaulniers5y ago0 comments

> and clang's previous performance advantages were actually due to the lack of various optimization techniques and other features?

Not lack of optimization techniques; LLVM is relatively fast compared to Clang for builds of the Linux kernel. Is it all of the compiler diagnostics and semantic analysis, or just unoptimized code? WIP to find out.

(I literally just went over a perf record of a linux kernel build with a teammate that's going to look into this more; I organized the LLVM miniconf at plumbers which is the video linked in the phoronix article in the grand parent post; my summer intern did the initial profiling work).

ToT LLVM, linux-next x86_64 defconfig: https://photos.app.goo.gl/hNwwy2K1Gh7Uc2D67 (yes, I know about disabling kptr_restrict)

Our next big project is to look into lazy parsing.

0 comments

2 comments · 1 top-level

hamandcheese5y ago· 1 in thread

I’m confused, I thought clang was a frontend for LLVM so how does it make sense to compare clang with LLVM?

From the clang Wikipedia:

> It uses the LLVM compiler infrastructure as its back end and has been part of the LLVM release cycle since LLVM 2.6.

ndesaulniersOP5y ago

It's a pipeline; clang starts, hands off to LLVM.

For a compilation to object file from source code, the vast majority of time for most translation units when building the Linux kernel is spent in the front end of the pipeline, not the middle, or backend.

1 more reply

j / k navigate · click thread line to collapse