[PATCH] D76273: [NFCI][SCEV] Avoid recursion in SCEVExpander::isHighCostExpansion*()

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: mkazantsev, reames, wmi, ekatz.
lebedev.ri added a project: LLVM.
Herald added subscribers: javed.absar, hiraditya.
lebedev.ri retitled this revision from "[SCEV] Avoid recursion in SCEVExpander::isHighCostExpansion*()" to "[NFCI][SCEV] Avoid recursion in SCEVExpander::isHighCostExpansion*()".

As noted in PR45201 <https://bugs.llvm.org/show_bug.cgi?id=45201>,
PR10090 <https://bugs.llvm.org/show_bug.cgi?id=10090> SCEV doesn't always avoid
recursive algorithms, and that causes issues with large expression depths and/or smaller stack sizes.

In `SCEVExpander::isHighCostExpansion*()` case, the refactoring to avoid recursion
is rather idiomatic. We simply need to place the root expr into a vector,
and iterate over vector elements accounting for the cost of each one,
and add new exprs at the end of the vector, thus achieving FIFO breadth-first traversal.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76273

Files:
  llvm/include/llvm/Analysis/ScalarEvolutionExpander.h
  llvm/lib/Analysis/ScalarEvolutionExpander.cpp

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