[PATCH] D120584: [NewPM][Inliner] Mark inlined calls to functions in same SCC as callee as noinline

[David Li via Phabricator via llvm-commits]

davidxl added inline comments.


================
Comment at: llvm/lib/Transforms/IPO/Inliner.cpp:952
+              if (CalleeSCC != C &&
+                  CalleeSCC == CG.lookupSCC(CG.get(*NewCallee))) {
+                ICB->addFnAttr(Attribute::NoInline);
----------------
nikic wrote:
> davidxl wrote:
> > This feels like very strict. Is it possible to allow some level (under an option) of iterative inlining into the same SCC?     This is because not all cases of inlining into a non-trivial SCC will result in compile time issue due to existing threshold based stopping mechanism (i.e. the new callee in SCC is too large).
> > 
> > 
> This does not restrict inlining into the same SCC. What it prevents is continuously peeling off more and more calls from a *different* non-trivial SCC.
> 
> From what I can tell, this is a rare case, only two programs in llvm-test-suite show any codegen changes with this patch.
To clarify, my understanding of the scenario is like the following


foo -->   (a, b, c)    where foo calls 'a'.

where a, b, and c forms anon trivial SCC.

Without the fix, we can end up with  inlining of foo->a, foo->b, foo->c, foo->a, foo->b, .... until foo blows up (we don't have a caller limit set in the inliner).

With this patch, once foo-> a is inlined, the new callsite foo->b is marked as no inline.

Is that the right?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D120584/new/

https://reviews.llvm.org/D120584