[PATCH] [SLPVectorization] Enhance Ability to Vectorize Horizontal Reductions from Consecutive Loads

[Michael Zolotukhin]

Hi Suyog,

Thanks for working on this, please find comments from me inline.

Michael


REPOSITORY
  rL LLVM

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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:1244
@@ -1236,2 +1243,3 @@
         reorderInputsAccordingToOpcode(VL, Left, Right);
+        reorderIfConsecutiveLoads (Left, Right);
         buildTree_rec(Left, Depth + 1);
----------------
No need in whitespace before the brace.

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Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:1838-1841
@@ +1837,6 @@
+      return;
+    if (!(isConsecutiveAccess(Left[i], Right[i])))
+      continue;
+    else
+      std::swap(Left[i + 1], Right[i]);
+  }
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I think we should only swap if `Left[i]` and `Left[i+1]` are consecutive - that's the only case we get something from this reordering.

In your current approach we might lose consecutiveness in `Right[i]` and `Right[i+1]` by swapping `Left[i+1]` and `Right[i]` even if later on `Left[i]` and `Left[i+1]` won't be consecutive.

================
Comment at: lib/Transforms/Vectorize/SLPVectorizer.cpp:2077
@@ -2052,1 +2076,3 @@
         reorderInputsAccordingToOpcode(E->Scalars, LHSVL, RHSVL);
+        reorderIfConsecutiveLoads (LHSVL, RHSVL);
+      }
----------------
Redundant whitespace here too.

http://reviews.llvm.org/D6675

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