[llvm] [LTO][Pipelines] Add 0 hot-caller threshold for SamplePGO + FullLTO (PR #135152)

[Mingming Liu via llvm-commits]

mingmingl-llvm wrote:

> If a hot callsite function is not inlined in the 1st build, inlining the hot callsite in pre-link stage of SPGO 2nd build may lead to Function Sample not found in profile file in link stage. ThinLTO has already considered and dealed with it by setting HotCallSiteThreshold to 0 to stop the inline. This patch just adds the same processing for FullLTO.

Do you have some build stats (e.g., functions miss profiles before and get profiles after, etc) or binary performance data for this FullLTO patch? 

Does 1st build refer to the profiled binary build here? I'm asking since the motivation for zero inline threshold in the ThinLTO prelink pipeline (before cross-module inline) is to make profile matching in the backend (after cross-module inline) more accurate within one build. I'm not sure if this zero inline threshold helps across build though. 



https://github.com/llvm/llvm-project/pull/135152