[libcxx-commits] [openmp] [clang-tools-extra] [libcxx] [lld] [flang] [clang] [llvm] [lldb] [mlir] [libc] [SLP]Add support for strided loads. (PR #80310)

[Philip Reames via libcxx-commits]

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@@ -3930,30 +4065,68 @@ static LoadsState canVectorizeLoads(ArrayRef<Value *> VL, const Value *VL0,
       std::optional<int> Diff =
           getPointersDiff(ScalarTy, Ptr0, ScalarTy, PtrN, DL, SE);
       // Check that the sorted loads are consecutive.
-      if (static_cast<unsigned>(*Diff) == VL.size() - 1)
+      if (static_cast<unsigned>(*Diff) == Sz - 1)
         return LoadsState::Vectorize;
       // Simple check if not a strided access - clear order.
-      IsPossibleStrided = *Diff % (VL.size() - 1) == 0;
+      bool IsPossibleStrided = *Diff % (Sz - 1) == 0;
+      // Try to generate strided load node if:
+      // 1. Target with strided load support is detected.
+      // 2. The number of loads is greater than MinProfitableStridedLoads,
+      // or the potential stride <= MaxProfitableLoadStride and the
+      // potential stride is power-of-2 (to avoid perf regressions for the very
+      // small number of loads) and max distance > number of loads, or potential
+      // stride is -1.
+      // 3. The loads are ordered, or number of unordered loads <=
+      // MaxProfitableUnorderedLoads, or loads are in reversed order.
+      // (this check is to avoid extra costs for very expensive shuffles).
+      if (IsPossibleStrided && (((Sz > MinProfitableStridedLoads ||
+                                  (static_cast<unsigned>(std::abs(*Diff)) <=
+                                       MaxProfitableLoadStride * Sz &&
+                                   isPowerOf2_32(std::abs(*Diff)))) &&
+                                 static_cast<unsigned>(std::abs(*Diff)) > Sz) ||
+                                *Diff == -(static_cast<int>(Sz) - 1))) {
+        int Stride = *Diff / static_cast<int>(Sz - 1);
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preames wrote:

How is the diff-in-bytes divided by the number of elements the stride?  Did you maybe mean to use element size here?

It's also possible you have two Sz variables with different meaning.  I did not check for this.

https://github.com/llvm/llvm-project/pull/80310