[llvm] [InstCombine] Simplify select if it combinated and/or/xor (PR #73362)

[via llvm-commits]

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@@ -1672,6 +1672,115 @@ static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
   return nullptr;
 }
 
+static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,
+                                     InstCombinerImpl &IC) {
+  ICmpInst::Predicate Pred = ICI->getPredicate();
+  if (!ICmpInst::isEquality(Pred))
+    return nullptr;
+
+  Value *TrueVal = SI.getTrueValue();
+  Value *FalseVal = SI.getFalseValue();
+  Value *CmpLHS = ICI->getOperand(0);
+  Value *CmpRHS = ICI->getOperand(1);
+
+  if (Pred == ICmpInst::ICMP_NE) {
+    Pred = ICmpInst::ICMP_EQ;
+    std::swap(TrueVal, FalseVal);
+  }
+
+  // Transform (X == C) ? X : Y -> (X == C) ? C : Y
+  // specific handling for Bitwise operation.
+  // https://alive2.llvm.org/ce/z/WW8iRR
+  // x&y -> (x|y) ^ (x^y)
+  // x|y -> (x&y) | (x^y)
+  // x^y -> (x|y) ^ (x&y)
+  Value *X, *Y;
+  if (!(match(CmpLHS, m_BitwiseLogic(m_Value(X), m_Value(Y)))) ||
+      !(match(TrueVal, m_BitwiseLogic(m_Specific(X), m_Specific(Y)))))
+    return nullptr;
+
+  Value *AllOnes = Constant::getAllOnesValue(TrueVal->getType());
+  Value *Null = Constant::getNullValue(TrueVal->getType());
+  Instruction *ISI = &cast<Instruction>(SI);
+  unsigned AndOps = Instruction::And, OrOps = Instruction::Or,
+           XorOps = Instruction::Xor, NoOps = 0;
+
+  auto matchFalseVal = [&](Value *FalseVal, Value *CmpRHS, Value *X, Value *Y,
+                           unsigned OuterOpc, unsigned InnerOpc, bool NotRHS) {
+    if (match(CmpRHS, m_Zero()))
+      return match(FalseVal, m_c_BinOp(InnerOpc, m_Specific(X), m_Specific(Y)));
+
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goldsteinn wrote:

If `OuterOpc == NoOps` you should just return false here.

https://github.com/llvm/llvm-project/pull/73362