[PATCH] D90125: [CSSPGO] Infrastructure for context-sensitive Sample PGO and Inlining

[Wei Mi via Phabricator via llvm-commits]

wmi added inline comments.


================
Comment at: llvm/lib/Transforms/IPO/SampleContextTracker.cpp:373
+
+ContextTrieNode *SampleContextTracker::getContextFor(const DILocation *DIL) {
+  assert(DIL);
----------------
wenlei wrote:
> wmi wrote:
> > A question, the context in SampleContextTracker includes not only inline stack but also call stack. S vector below only contains the inline stack at the DIL location. How can it match with the full stack starting from RootContext?  
> When we decided to not inline a call site, context profile will be promoted to root, so what remains in context tracker should reflect the accurate remainder context profile. E.g. if we start with A->(call) B->(inline) C in context tracker. At some point if we're looking at B->C from DIL, there're two scenarios:
> 
> 1. If A inlined B, in this case, we wouldn't be able to match B->C from DIL to anything in context tracker. But this is intentional and desired, because The remainder/base profile for B, or the context profile B->C shouldn't have anything if A->B inline happened. 
> 2. If A not inlined B, in this case, B->C should be moved/promoted from child of A to be under root. Then we would be able to match B->C from DIL to B->C (under root) in context tracker. 
I see, thanks. After compiler decides it won't inline at some callsite, the profile for the callsite will be promoted and some context information will be loss. This seems to assume the inlining happens in top-down order and happens only once. I remember the CSSPGO profile will be used to drive CGSCC Inliner in the future. CGSCC Inliner will need to do the inlining iteratively so how it supposes to work with profile promotion?


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  https://reviews.llvm.org/D90125/new/

https://reviews.llvm.org/D90125