[llvm] [VectorCombine] Scalarize bin ops and cmps with two splatted operands (PR #137786)

[Philip Reames via llvm-commits]

================
@@ -1035,50 +1035,61 @@ bool VectorCombine::scalarizeBinopOrCmp(Instruction &I) {
       if (match(U, m_Select(m_Specific(&I), m_Value(), m_Value())))
         return false;
 
-  // Match against one or both scalar values being inserted into constant
-  // vectors:
-  // vec_op VecC0, (inselt VecC1, V1, Index)
-  // vec_op (inselt VecC0, V0, Index), VecC1
-  // vec_op (inselt VecC0, V0, Index), (inselt VecC1, V1, Index)
-  // TODO: Deal with mismatched index constants and variable indexes?
   Constant *VecC0 = nullptr, *VecC1 = nullptr;
   Value *V0 = nullptr, *V1 = nullptr;
-  uint64_t Index0 = 0, Index1 = 0;
-  if (!match(Ins0, m_InsertElt(m_Constant(VecC0), m_Value(V0),
-                               m_ConstantInt(Index0))) &&
-      !match(Ins0, m_Constant(VecC0)))
-    return false;
-  if (!match(Ins1, m_InsertElt(m_Constant(VecC1), m_Value(V1),
-                               m_ConstantInt(Index1))) &&
-      !match(Ins1, m_Constant(VecC1)))
-    return false;
+  std::optional<uint64_t> Index;
+
+  // Try and match against two splatted operands first.
+  // vec_op (splat V0), (splat V1)
+  V0 = getSplatValue(Ins0);
+  V1 = getSplatValue(Ins1);
+  if (!V0 || !V1) {
+    // Match against one or both scalar values being inserted into constant
+    // vectors:
+    // vec_op VecC0, (inselt VecC1, V1, Index)
+    // vec_op (inselt VecC0, V0, Index), VecC1
+    // vec_op (inselt VecC0, V0, Index), (inselt VecC1, V1, Index)
+    // TODO: Deal with mismatched index constants and variable indexes?
+    V0 = nullptr, V1 = nullptr;
+    uint64_t Index0 = 0, Index1 = 0;
+    if (!match(Ins0, m_InsertElt(m_Constant(VecC0), m_Value(V0),
+                                 m_ConstantInt(Index0))) &&
+        !match(Ins0, m_Constant(VecC0)))
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preames wrote:

It looks like the prior code did handle constant splats here.  I think most of the m_Constant dependent bits become dead with your change?  Of, this is because of the coupled condition noted just above.

https://github.com/llvm/llvm-project/pull/137786