Revert "[IR][LoopRotate] avoid leaving phi with no operands (PR48296)"

This reverts commit bfd2c21. This appears to be causing stage2 msan failures on buildbots: FAIL: LLVM :: Transforms/SimplifyCFG/X86/bug-25299.ll (65872 of 71835) ******************** TEST 'LLVM :: Transforms/SimplifyCFG/X86/bug-25299.ll' FAILED ******************** Script: -- : 'RUN: at line 1'; /b/sanitizer-x86_64-linux-fast/build/llvm_build_msan/bin/opt < /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/test/Transforms/SimplifyCFG/X86/bug-25299.ll -simplifycfg -S | /b/sanitizer-x86_64-linux-fast/build/llvm_build_msan/bin/FileCheck /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/test/Transforms/SimplifyCFG/X86/bug-25299.ll -- Exit Code: 2 Command Output (stderr): -- ==87374==WARNING: MemorySanitizer: use-of-uninitialized-value #0 0x9de47b6 in getBasicBlockIndex /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/include/llvm/IR/Instructions.h:2749:5 #1 0x9de47b6 in simplifyCommonResume /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:4112:23 rust-lang#2 0x9de47b6 in simplifyResume /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:4039:12 rust-lang#3 0x9de47b6 in (anonymous namespace)::SimplifyCFGOpt::simplifyOnce(llvm::BasicBlock*) /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6330:16 rust-lang#4 0x9dcca13 in run /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6358:16 rust-lang#5 0x9dcca13 in llvm::simplifyCFG(llvm::BasicBlock*, llvm::TargetTransformInfo const&, llvm::SimplifyCFGOptions const&, llvm::SmallPtrSetImpl<llvm::BasicBlock*>*) /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6369:8 rust-lang#6 0x974643d in iterativelySimplifyCFG(
nikic · Nov 30, 2020 · 355aee3 · 355aee3
1 parent 78c7118
commit 355aee3
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Showing 3 changed files with 4 additions and 38 deletions.
diff --git a/llvm/include/llvm/IR/BasicBlock.h b/llvm/include/llvm/IR/BasicBlock.h
@@ -387,9 +387,9 @@ class BasicBlock final : public Value, // Basic blocks are data objects also
   /// Update PHI nodes in this BasicBlock before removal of predecessor \p Pred.
   /// Note that this function does not actually remove the predecessor.
   ///
-  /// If \p KeepOneInputPHIs is true, then don't remove PHIs that are left with
-  /// one incoming value and don't simplify PHIs with all incoming values the
-  /// same.
+  /// If \p KeepOneInputPHIs is true then don't remove PHIs that are left with
+  /// zero or one incoming values, and don't simplify PHIs with all incoming
+  /// values the same.
   void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs = false);
 
   bool canSplitPredecessors() const;

diff --git a/llvm/lib/IR/BasicBlock.cpp b/llvm/lib/IR/BasicBlock.cpp
@@ -330,7 +330,7 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
 
   unsigned NumPreds = cast<PHINode>(front()).getNumIncomingValues();
   for (PHINode &Phi : make_early_inc_range(phis())) {
-    Phi.removeIncomingValue(Pred);
+    Phi.removeIncomingValue(Pred, !KeepOneInputPHIs);
     if (KeepOneInputPHIs)
       continue;
     // If we have a single predecessor, removeIncomingValue erased the PHI

diff --git a/llvm/test/Transforms/LoopRotate/phi-empty.ll b/llvm/test/Transforms/LoopRotate/phi-empty.ll