[llvm] [InstCombine] Introduce `foldICmpBinOpWithConstantViaTruthTable` folding (PR #139109)

[Nikita Popov via llvm-commits]

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@@ -3110,6 +3086,45 @@ static Value *createLogicFromTable(const std::bitset<4> &Table, Value *Op0,
   return nullptr;
 }
 
+Instruction *InstCombinerImpl::foldICmpBinOpWithConstantViaTruthTable(
+    ICmpInst &Cmp, BinaryOperator *BO, const APInt &C) {
+  Value *A, *B;
+  Constant *C1, *C2, *C3, *C4;
+  if (match(BO->getOperand(0),
+            m_Select(m_Value(A), m_Constant(C1), m_Constant(C2))) &&
+      match(BO->getOperand(1),
+            m_Select(m_Value(B), m_Constant(C3), m_Constant(C4))) &&
+      Cmp.getType() == A->getType()) {
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nikic wrote:

Early return?

https://github.com/llvm/llvm-project/pull/139109