[SLP] Fix for PR30626: Compiler crash inside SLP Vectorizer.

After successfull horizontal reduction vectorization attempt for PHI node
vectorizer tries to update root binary op by combining vectorized tree
and the ReductionPHI node. But during vectorization this ReductionPHI
can be vectorized itself and replaced by the `undef` value, while the
instruction itself is marked for deletion. This 'marked for deletion'
PHI node then can be used in new binary operation, causing "Use still
stuck around after Def is destroyed" crash upon PHI node deletion.

Also the test is fixed to make it perform actual testing.

Differential Revision: https://reviews.llvm.org/D25671

llvm-svn: 285286

1 files changed, 11 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 47a6d0434b2..73dca758dd6 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -4062,7 +4062,14 @@ class HorizontalReduction {
   SmallVector<Value *, 32> ReducedVals;
 
   BinaryOperator *ReductionRoot;
-  PHINode *ReductionPHI;
+  // After successfull horizontal reduction vectorization attempt for PHI node
+  // vectorizer tries to update root binary op by combining vectorized tree and
+  // the ReductionPHI node. But during vectorization this ReductionPHI can be
+  // vectorized itself and replaced by the undef value, while the instruction
+  // itself is marked for deletion. This 'marked for deletion' PHI node then can
+  // be used in new binary operation, causing "Use still stuck around after Def
+  // is destroyed" crash upon PHI node deletion.
+  WeakVH ReductionPHI;
 
   /// The opcode of the reduction.
   unsigned ReductionOpcode;
@@ -4081,8 +4088,8 @@ public:
   unsigned MinVecRegSize;
 
   HorizontalReduction(unsigned MinVecRegSize)
-      : ReductionRoot(nullptr), ReductionPHI(nullptr), ReductionOpcode(0),
-        ReducedValueOpcode(0), IsPairwiseReduction(false), ReduxWidth(0),
+      : ReductionRoot(nullptr), ReductionOpcode(0), ReducedValueOpcode(0),
+        IsPairwiseReduction(false), ReduxWidth(0),
         MinVecRegSize(MinVecRegSize) {}
 
   /// \brief Try to find a reduction tree.
@@ -4247,7 +4254,7 @@ public:
                                      ReducedVals[i]);
       }
       // Update users.
-      if (ReductionPHI) {
+      if (ReductionPHI && !isa<UndefValue>(ReductionPHI)) {
         assert(ReductionRoot && "Need a reduction operation");
         ReductionRoot->setOperand(0, VectorizedTree);
         ReductionRoot->setOperand(1, ReductionPHI);