[PATCH] D64404: [SimpleLoopUnswitch] Don't consider unswitching `switch` insructions with one unique successor

[Daniil Suchkov via Phabricator via llvm-commits]

DaniilSuchkov created this revision.
DaniilSuchkov added reviewers: asbirlea, reames.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
DaniilSuchkov added a parent revision: D64403: [SimpleLoopUnswitch] Add a test case exposing a bug.

Currently SimpleLoopUnswitch considers unswitching any `switch` instructions, in case if the instruction has only one unique successor it causes crash on `assert(SuccessorsCount > 1 && "Cannot unswitch a condition without multiple distinct successors!")`.


https://reviews.llvm.org/D64404

Files:
  llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
  llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-redundant-switch.ll


Index: llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-redundant-switch.ll
===================================================================
--- llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-redundant-switch.ll
+++ llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-redundant-switch.ll
@@ -1,5 +1,4 @@
 ; REQUIRES: asserts
-; XFAIL: *
 ; RUN: opt -passes='unswitch<nontrivial>' -disable-output -S < %s
 ; RUN: opt -simple-loop-unswitch -enable-nontrivial-unswitch -disable-output -S < %s
 
Index: llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2549,10 +2549,11 @@
         }
 
     if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
+      const bool HasAtLeastTwoSuccessors = BB->getUniqueSuccessor() == nullptr;
       // We can only consider fully loop-invariant switch conditions as we need
       // to completely eliminate the switch after unswitching.
       if (!isa<Constant>(SI->getCondition()) &&
-          L.isLoopInvariant(SI->getCondition()))
+          L.isLoopInvariant(SI->getCondition()) && HasAtLeastTwoSuccessors)
         UnswitchCandidates.push_back({SI, {SI->getCondition()}});
       continue;
     }


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