[PATCH] D38138: [SimplifyCFG] add a struct to house optional folds (PR34603)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
Herald added subscribers: JDevlieghere, nhaehnle, mcrosier, arsenm.

This was intended to be no-functional-change, but it's not - there's a test diff.

So I thought I should stop here and post it as-is to see if this looks like what was expected based on the discussion in PR34603:
https://bugs.llvm.org/show_bug.cgi?id=34603

Notes:

1. The test improvement occurs because the existing 'LateSimplifyCFG' marker is not carried through the recursive calls to 'SimplifyCFG()->SimplifyCFGOpt().run()->SimplifyCFG()'. The parameter isn't passed down, so we pick up the default value from the function signature after the first level. I assumed that was a bug, so I've passed 'Options' down in all of the 'SimplifyCFG' calls.

2. I split 'LateSimplifyCFG' into 2 bits: ConvertSwitchToLookupTable and KeepCanonicalLoops. This would theoretically allow us to differentiate the transforms controlled by those params independently.

3. We could stash the optional AssumptionCache pointer and 'LoopHeaders' pointer in the struct too. I just stopped here to minimize the diffs.

4. Similarly, I stopped short of messing with the pass manager layer. I have another question that could wait for the follow-up assuming this patch is headed in the right direction: why is the new pass manager creating the pass with LateSimplifyCFG set to true no matter where in the pipeline it's creating SimplifyCFG passes? // Create an early function pass manager to cleanup the output of the // frontend. EarlyFPM.addPass(SimplifyCFGPass());

-->
 /// \brief Construct a pass with the default thresholds
 /// and switch optimizations.
 SimplifyCFGPass::SimplifyCFGPass()

  : BonusInstThreshold(UserBonusInstThreshold),
    LateSimplifyCFG(true) {}   <-- switches get converted to lookup tables and loops may not be in canonical form

If this is unintended, then it's possible that the current behavior of dropping the 'LateSimplifyCFG' setting via recursion was masking this bug.


https://reviews.llvm.org/D38138

Files:
  include/llvm/Transforms/Scalar/SimplifyCFG.h
  include/llvm/Transforms/Utils/Local.h
  lib/CodeGen/DwarfEHPrepare.cpp
  lib/Target/AMDGPU/AMDGPUUnifyDivergentExitNodes.cpp
  lib/Transforms/Scalar/SimplifyCFGPass.cpp
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
  tools/bugpoint/CrashDebugger.cpp

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