[PATCH] D29641: [SLP] Fix for PR31847: Assertion failed: (isLoopInvariant(Operands[i], L) && "SCEVAddRecExpr operand is not loop-invariant!")

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
Herald added a subscriber: sanjoy.

If the loop body has changed and ScalarEvolution is used in the code, then forgetLoopDispositions() function must be called for the loop. Otherwise, SCEV info may be reused and this may cause a crash of the compiler.


https://reviews.llvm.org/D29641

Files:
  lib/Transforms/Vectorize/SLPVectorizer.cpp


Index: lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -3719,6 +3719,33 @@
   return PA;
 }
 
+namespace {
+/// Class tracks changes in the basic block and if something has changed and
+/// this basic block is part of the loop it communicates ScalarEvolution to
+/// forget an existing loop dispositions. Otherwise we may to reuse
+/// ScalarEvolution nodes and get wrong info about loop dispositions.
+class TrackChanges {
+private:
+  ScalarEvolution *SE = nullptr;
+  const LoopInfo *LI = nullptr;
+  const BasicBlock *BB = nullptr;
+  bool Changed = false;
+
+public:
+  TrackChanges(ScalarEvolution *SE, const LoopInfo *LI) : SE(SE), LI(LI) {}
+  void setBasicBlock(const BasicBlock *B) { BB = B; }
+  TrackChanges &operator|=(bool C) {
+    if (C) {
+      if (const Loop *L = LI->getLoopFor(BB))
+        SE->forgetLoopDispositions(L);
+      Changed = true;
+    }
+    return *this;
+  }
+  operator bool() const { return Changed; }
+};
+} // namespace
+
 bool SLPVectorizerPass::runImpl(Function &F, ScalarEvolution *SE_,
                                 TargetTransformInfo *TTI_,
                                 TargetLibraryInfo *TLI_, AliasAnalysis *AA_,
@@ -3736,7 +3763,7 @@
 
   Stores.clear();
   GEPs.clear();
-  bool Changed = false;
+  TrackChanges Changed(SE, LI);
 
   // If the target claims to have no vector registers don't attempt
   // vectorization.
@@ -3758,6 +3785,7 @@
 
   // Scan the blocks in the function in post order.
   for (auto BB : post_order(&F.getEntryBlock())) {
+    Changed.setBasicBlock(BB);
     collectSeedInstructions(BB);
 
     // Vectorize trees that end at stores.


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