[llvm] [InstCombine] simplify `icmp pred x, ~x` (PR #73990)

[via llvm-commits]

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@@ -4540,14 +4540,45 @@ static Instruction *foldICmpXorXX(ICmpInst &I, const SimplifyQuery &Q,
   if (!match(Op0, m_c_Xor(m_Specific(Op1), m_Value(A))))
     return nullptr;
 
+  CmpInst::Predicate StrictPred = ICmpInst::getStrictPredicate(Pred);
+  // Transform
+  // X s< ~X, X s<= ~X, X u> ~X, X u>= ~X
+  // --> X s< 0
+  // X s> ~X, X s>= ~X, X u< ~X, X u<= ~X
+  // --> X s> -1
+  // X ==  ~X  -->   false
+  // X !=  ~X  -->   true
+  if (match(Op0, m_Not(m_Specific(Op1)))) {
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goldsteinn wrote:

These all work for any `xor x, neg_C`:
https://alive2.llvm.org/ce/z/6LR8Nn



https://github.com/llvm/llvm-project/pull/73990