[llvm] r277728 - [X86][SSE] Split off shuffle mask canonicalization from lowerVectorShuffle. NFCI.

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Thu Aug  4 09:21:32 2016
New Revision: 277728

URL: http://llvm.org/viewvc/llvm-project?rev=277728&view=rev
Log:
[X86][SSE] Split off shuffle mask canonicalization from lowerVectorShuffle. NFCI.

The new function now returns true if the shuffle should be commuted.

This will allow target shuffle combines to share the code.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=277728&r1=277727&r2=277728&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Thu Aug  4 09:21:32 2016
@@ -12171,6 +12171,71 @@ static SDValue lower1BitVectorShuffle(co
   return DAG.getNode(ISD::TRUNCATE, DL, VT,
                      DAG.getVectorShuffle(ExtVT, DL, V1, V2, Mask));
 }
+
+/// Helper function that returns true if the shuffle mask should be
+/// commuted to improve canonicalization.
+static bool canonicalizeShuffleMaskWithCommute(ArrayRef<int> Mask) {
+  int NumElements = Mask.size();
+
+  int NumV1Elements = 0, NumV2Elements = 0, NumSentinelElements = 0;
+  for (int M : Mask)
+    if (M < 0)
+      ++NumSentinelElements;
+    else if (M < NumElements)
+      ++NumV1Elements;
+    else
+      ++NumV2Elements;
+
+  // Commute the shuffle as needed such that more elements come from V1 than
+  // V2. This allows us to match the shuffle pattern strictly on how many
+  // elements come from V1 without handling the symmetric cases.
+  if (NumV2Elements > NumV1Elements)
+    return true;
+
+  assert(NumV1Elements > 0 && "No V1 indices");
+
+  if (NumV2Elements == 0)
+    return false;
+
+  // When the number of V1 and V2 elements are the same, try to minimize the
+  // number of uses of V2 in the low half of the vector. When that is tied,
+  // ensure that the sum of indices for V1 is equal to or lower than the sum
+  // indices for V2. When those are equal, try to ensure that the number of odd
+  // indices for V1 is lower than the number of odd indices for V2.
+  if (NumV1Elements == NumV2Elements) {
+    int LowV1Elements = 0, LowV2Elements = 0;
+    for (int M : Mask.slice(0, NumElements / 2))
+      if (M >= NumElements)
+        ++LowV2Elements;
+      else if (M >= 0)
+        ++LowV1Elements;
+    if (LowV2Elements > LowV1Elements)
+      return true;
+    if (LowV2Elements == LowV1Elements) {
+      int SumV1Indices = 0, SumV2Indices = 0;
+      for (int i = 0, Size = Mask.size(); i < Size; ++i)
+        if (Mask[i] >= NumElements)
+          SumV2Indices += i;
+        else if (Mask[i] >= 0)
+          SumV1Indices += i;
+      if (SumV2Indices < SumV1Indices)
+        return true;
+      if (SumV2Indices == SumV1Indices) {
+        int NumV1OddIndices = 0, NumV2OddIndices = 0;
+        for (int i = 0, Size = Mask.size(); i < Size; ++i)
+          if (Mask[i] >= NumElements)
+            NumV2OddIndices += i % 2;
+          else if (Mask[i] >= 0)
+            NumV1OddIndices += i % 2;
+        if (NumV2OddIndices < NumV1OddIndices)
+          return true;
+      }
+    }
+  }
+
+  return false;
+}
+
 /// \brief Top-level lowering for x86 vector shuffles.
 ///
 /// This handles decomposition, canonicalization, and lowering of all x86
@@ -12244,60 +12309,10 @@ static SDValue lowerVectorShuffle(SDValu
     }
   }
 
-  int NumV1Elements = 0, NumUndefElements = 0, NumV2Elements = 0;
-  for (int M : Mask)
-    if (M < 0)
-      ++NumUndefElements;
-    else if (M < NumElements)
-      ++NumV1Elements;
-    else
-      ++NumV2Elements;
-
-  // Commute the shuffle as needed such that more elements come from V1 than
-  // V2. This allows us to match the shuffle pattern strictly on how many
-  // elements come from V1 without handling the symmetric cases.
-  if (NumV2Elements > NumV1Elements)
+  // Commute the shuffle if it will improve canonicalization.
+  if (canonicalizeShuffleMaskWithCommute(Mask))
     return DAG.getCommutedVectorShuffle(*SVOp);
 
-  assert(NumV1Elements > 0 && "No V1 indices");
-  assert((NumV2Elements > 0 || V2IsUndef) && "V2 not undef, but not used");
-
-  // When the number of V1 and V2 elements are the same, try to minimize the
-  // number of uses of V2 in the low half of the vector. When that is tied,
-  // ensure that the sum of indices for V1 is equal to or lower than the sum
-  // indices for V2. When those are equal, try to ensure that the number of odd
-  // indices for V1 is lower than the number of odd indices for V2.
-  if (NumV1Elements == NumV2Elements) {
-    int LowV1Elements = 0, LowV2Elements = 0;
-    for (int M : Mask.slice(0, NumElements / 2))
-      if (M >= NumElements)
-        ++LowV2Elements;
-      else if (M >= 0)
-        ++LowV1Elements;
-    if (LowV2Elements > LowV1Elements)
-      return DAG.getCommutedVectorShuffle(*SVOp);
-    if (LowV2Elements == LowV1Elements) {
-      int SumV1Indices = 0, SumV2Indices = 0;
-      for (int i = 0, Size = Mask.size(); i < Size; ++i)
-        if (Mask[i] >= NumElements)
-          SumV2Indices += i;
-        else if (Mask[i] >= 0)
-          SumV1Indices += i;
-      if (SumV2Indices < SumV1Indices)
-        return DAG.getCommutedVectorShuffle(*SVOp);
-      if (SumV2Indices == SumV1Indices) {
-        int NumV1OddIndices = 0, NumV2OddIndices = 0;
-        for (int i = 0, Size = Mask.size(); i < Size; ++i)
-          if (Mask[i] >= NumElements)
-            NumV2OddIndices += i % 2;
-          else if (Mask[i] >= 0)
-            NumV1OddIndices += i % 2;
-        if (NumV2OddIndices < NumV1OddIndices)
-          return DAG.getCommutedVectorShuffle(*SVOp);
-      }
-    }
-  }
-
   // For each vector width, delegate to a specialized lowering routine.
   if (VT.is128BitVector())
     return lower128BitVectorShuffle(DL, Mask, VT, V1, V2, Subtarget, DAG);