[llvm-branch-commits] [llvm] 355aee3 - Revert "[IR][LoopRotate] avoid leaving phi with no operands (PR48296)"

[Sanjay Patel via llvm-branch-commits]

Author: Sanjay Patel
Date: 2020-11-30T10:15:42-05:00
New Revision: 355aee3dcd441461a6da6e56c43dc1bd81c79f31

URL: https://github.com/llvm/llvm-project/commit/355aee3dcd441461a6da6e56c43dc1bd81c79f31
DIFF: https://github.com/llvm/llvm-project/commit/355aee3dcd441461a6da6e56c43dc1bd81c79f31.diff

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

This reverts commit bfd2c216ea8ef09f8fb1f755ca2b89f86f74acbb.
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
      #2 0x9de47b6 in simplifyResume /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:4039:12
      #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
      #4 0x9dcca13 in run /b/sanitizer-x86_64-linux-fast/build/llvm-project/llvm/lib/Transforms/Utils/SimplifyCFG.cpp:6358:16
      #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
      #6 0x974643d in iterativelySimplifyCFG(

Added: 
    

Modified: 
    llvm/include/llvm/IR/BasicBlock.h
    llvm/lib/IR/BasicBlock.cpp

Removed: 
    llvm/test/Transforms/LoopRotate/phi-empty.ll


################################################################################
diff  --git a/llvm/include/llvm/IR/BasicBlock.h b/llvm/include/llvm/IR/BasicBlock.h
index 149b0a26c1f3..26cfdd9e51d6 100644
--- 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
index aee769aa0fea..3268641ddf19 100644
--- 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
deleted file mode 100644
index e246cff91b62..000000000000
--- a/llvm/test/Transforms/LoopRotate/phi-empty.ll
+++ /dev/null
@@ -1,34 +0,0 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -lcssa -loop-rotate < %s | FileCheck %s
-
-define void @PR48296(i1 %cond) {
-; CHECK-LABEL: @PR48296(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label [[LOOP:%.*]]
-; CHECK:       loop:
-; CHECK-NEXT:    br i1 [[COND:%.*]], label [[INC:%.*]], label [[LOOP_BACKEDGE:%.*]]
-; CHECK:       loop.backedge:
-; CHECK-NEXT:    br label [[LOOP]]
-; CHECK:       dead:
-; CHECK-NEXT:    unreachable
-; CHECK:       inc:
-; CHECK-NEXT:    br label [[LOOP_BACKEDGE]]
-; CHECK:       return:
-; CHECK-NEXT:    ret void
-;
-entry:
-  br label %loop
-
-loop:
-  br i1 %cond, label %inc, label %loop
-
-dead:                                        ; No predecessors!
-  br i1 %cond, label %inc, label %return
-
-inc:
-  br label %loop
-
-return:
-  %r = phi i32 [ undef, %dead ]
-  ret void
-}