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

[via llvm-commits]

================
@@ -1672,6 +1672,110 @@ 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);
+  }
+
+  if (!isa<BinaryOperator>(CmpLHS) || !isa<BinaryOperator>(TrueVal))
+    return nullptr;
+
+  // Transform (X == C) ? X : Y -> (X == C) ? C : Y
+  // specific handling for and/or/xor bit 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;
+  Value *AllOnes = Constant::getAllOnesValue(TrueVal->getType());
+  Value *Null = Constant::getNullValue(TrueVal->getType());
+  Instruction *ISI = &cast<Instruction>(SI);
+
+  // https://alive2.llvm.org/ce/z/EzU4sx
+  // (X & Y) == C ? X | Y : X ^ Y  ->  (X & Y) == C ?  C | (X^Y) : X ^ Y
+  // (X & Y) == C ? X ^ Y : X | Y  ->  (X & Y) == C ? ~C & (X|Y) : X | Y
----------------
goldsteinn wrote:

The header comments (here and below) no longer match the impl.

Here for example it is:
`(X & Y) == C ? X | Y : (X ^ Y) | C -> (X ^ Y) | C`


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