[llvm] [LoopVectorize] Add support for vectorisation of more early exit loops (PR #88385)

[Florian Hahn via llvm-commits]

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@@ -1489,4 +1489,82 @@ void InterleaveGroup<Instruction>::addMetadata(Instruction *NewInst) const {
                  [](std::pair<int, Instruction *> p) { return p.second; });
   propagateMetadata(NewInst, VL);
 }
+
+bool loopMayFault(const Loop *L, ScalarEvolution *SE,
+                  const DenseMap<Value *, SmallVector<const Value *, 16>>
+                      &UnderlyingObjects) {
+  auto &DL = L->getHeader()->getModule()->getDataLayout();
+  for (auto &UO : UnderlyingObjects) {
+    // TODO: For now if we encounter more than one underlying object we just
+    // assume it could fault. However, with more analysis it's possible to look
+    // at all of them and calculate a common range of permitted GEP indices.
+    if (UO.second.size() != 1)
+      return true;
+
+    // For now only the simplest cases are permitted, but this could be
+    // extended further.
+    auto *GEP = dyn_cast<GetElementPtrInst>(UO.first);
+    if (!GEP || GEP->getPointerOperand() != UO.second[0])
+      return true;
+
+    // The only current supported case for 2 GEP indices is when accessing an
+    // array, i.e.
+    //   getelementptr [32 x i32], ptr %arr, i64 0, i64 %ind
+    Value *GEPInd;
+    Type *GEPElemType;
+    if (GEP->getNumIndices() == 2) {
+      auto *ArrayTy = dyn_cast<ArrayType>(GEP->getSourceElementType());
+      if (!ArrayTy || !isa<ConstantInt>(GEP->getOperand(1)) ||
+          !cast<ConstantInt>(GEP->getOperand(1))->isZero())
+        return true;
+      GEPInd = GEP->getOperand(2);
+      GEPElemType = ArrayTy->getElementType();
+    } else if (GEP->getNumIndices() == 1) {
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fhahn wrote:

Why are those restrictions needed when we later use the SCEV of the GEP? If possible, would be good to use isDereferenceableAndAlignedInLoop instead of duplicating its logic.


https://github.com/llvm/llvm-project/pull/88385