[PATCH] D98481: [Inliner] Do not inline mutual-recursive functions to avoid exponential size growth.

[Hongtao Yu via Phabricator via llvm-commits]

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This change avoids inlining a function involved in a mutual-recursive cycle. Due to the lack of a global inline history, such inlining may cause an exponential size growth as the inlining extends up along the call graph.

Consider the following example,

  void A() { B(); B();}
  void B() { A(); }
  void C() { B(); }
  void D() { C(); }

When processing C, inlining B will result in

  void C() { B(); B(); }

When processing D, inlining C and futher the two B callsites will result in

  void D() { B(); B(); B(); B(); }

We've also seen that one of our internal services suffered from the inliner hanging for 6 hours.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98481

Files:
  llvm/lib/Transforms/IPO/Inliner.cpp
  llvm/test/Transforms/Inline/recursion.ll

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