[VPlan] Simplify select !c, x, y -> select c, y, x

This is split off from llvm#133993

On its own this simplification isn't that useful, but it allows us to make the equivalent VPBlendRecipe optimisation more generic by operating on VPInstructions.

In order to actually test this without llvm#133993, I've had to also extend the m_Not pattern matcher to also catch VPWidenRecipes, since I couldn't really think of a straightforward way to create a VPInstruction::Select with a negated condition.

Author: lukel97

llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h

@@ -366,12 +366,6 @@ m_Freeze(const Op0_t &Op0) {
   return m_VPInstruction<Instruction::Freeze>(Op0);
 }
 
-template <typename Op0_t>
-inline UnaryVPInstruction_match<Op0_t, VPInstruction::Not>
-m_Not(const Op0_t &Op0) {
-  return m_VPInstruction<VPInstruction::Not>(Op0);
-}
-
 template <typename Op0_t>
 inline UnaryVPInstruction_match<Op0_t, VPInstruction::BranchOnCond>
 m_BranchOnCond(const Op0_t &Op0) {
@@ -491,6 +485,15 @@ m_Select(const Op0_t &Op0, const Op1_t &Op1, const Op2_t &Op2) {
       {Op0, Op1, Op2});
 }
 
+template <typename Op0_t>
+inline match_combine_or<UnaryVPInstruction_match<Op0_t, VPInstruction::Not>,
+                        AllBinaryRecipe_match<int_pred_ty<is_all_ones>, Op0_t,
+                                              Instruction::Xor, true>>
+m_Not(const Op0_t &Op0) {
+  return m_CombineOr(m_VPInstruction<VPInstruction::Not>(Op0),
+                     m_c_Binary<Instruction::Xor>(m_AllOnes(), Op0));
+}
+
 template <typename Op0_t, typename Op1_t>
 inline match_combine_or<
     BinaryVPInstruction_match<Op0_t, Op1_t, VPInstruction::LogicalAnd>,

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1082,6 +1082,15 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
   if (match(Def, m_Select(m_VPValue(), m_VPValue(X), m_Deferred(X))))
     return Def->replaceAllUsesWith(X);
 
+  // select !c, x, y -> select c, y, x
+  VPValue *C;
+  if (match(Def, m_Select(m_Not(m_VPValue(C)), m_VPValue(X), m_VPValue(Y)))) {
+    Def->setOperand(0, C);
+    Def->setOperand(1, Y);
+    Def->setOperand(2, X);
+    return;
+  }
+
   if (match(Def, m_c_Mul(m_VPValue(A), m_SpecificInt(1))))
     return Def->replaceAllUsesWith(A);
 

llvm/test/Transforms/LoopVectorize/select-neg-cond.ll

@@ -13,8 +13,7 @@ define void @neg_cond(ptr noalias %p, ptr noalias %q) {
 ; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr i32, ptr [[P]], i32 [[INDEX]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, ptr [[TMP0]], i32 0
 ; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i32>, ptr [[TMP1]], align 4
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq <4 x i32> [[WIDE_LOAD]], splat (i32 42)
-; CHECK-NEXT:    [[TMP3:%.*]] = xor <4 x i1> [[TMP2]], splat (i1 true)
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne <4 x i32> [[WIDE_LOAD]], splat (i32 42)
 ; CHECK-NEXT:    [[TMP4:%.*]] = select <4 x i1> [[TMP3]], <4 x i32> splat (i32 42), <4 x i32> splat (i32 43)
 ; CHECK-NEXT:    store <4 x i32> [[TMP4]], ptr [[TMP1]], align 4
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4