[PATCH] D111687: Fix getInlineCost with ComputeFullInlineCost enabled

[Artur Pilipenko via Phabricator via llvm-commits]

apilipenko created this revision.
apilipenko added reviewers: mtrofin, aeubanks, taolq, DaniilSuchkov.
Herald added subscribers: wenlei, haicheng, hiraditya, eraman.
apilipenko requested review of this revision.
Herald added a project: LLVM.

getInlineCost delegates to InlineCostCallAnalyzer::analyze to do the actual analysis. Once the analysis is done getInlineCost tries to reverse engineer the result of the analysis in order to determine whether a detailed cost/threshold or a simple always/never should be returned.

  // Check if there was a reason to force inlining or no inlining.
  if (!ShouldInline.isSuccess() && CA.getCost() < CA.getThreshold())
    return InlineCost::getNever(ShouldInline.getFailureReason());
  if (ShouldInline.isSuccess() && CA.getCost() >= CA.getThreshold())
    return InlineCost::getAlways("empty function");
  
  return llvm::InlineCost::get(CA.getCost(), CA.getThreshold());

This reverse engineering fails when ComputeFullInlineCost is enabled. Specifically, InlineCostCallAnalyzer::analyze can fail due to non-inlinable instruction (e.g. noduplicate call). With ComputeFullInlineCost enabled the cost can be above the threshold. In this case, the old code incorrectly returns a cost/threshold pair instead of never.

We ran across this issue with a downstream user of InlineCost. I found that upstream SampleProfile uses getInlineCost with ComputeFullInlineCost, so I added a test case demonstrating the issue via SampleProfile.

To fix this issue I mimic the approach used by cost-benefit analysis and add an explicit flag to InlineCostCallAnalyzer indicating that the result was decided by cost-threshold analysis.


https://reviews.llvm.org/D111687

Files:
  llvm/lib/Analysis/InlineCost.cpp
  llvm/test/Transforms/SampleProfile/inline-noduplicate.ll

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