[llvm] [InstCombine] Try optimizing with knownbits which determined from Cond (PR #91762)

[via llvm-commits]

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@@ -1809,6 +1809,198 @@ static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,
   return nullptr;
 }
 
+// ICmpInst of SelectInst is not included in the calculation of KnownBits
+// so we are missing the opportunity to optimize the Value of the True or
+// False Condition via ICmpInst with KnownBits.
+//
+// Consider:
+//   %or = or i32 %x, %y
+//   %or0 = icmp eq i32 %or, 0
+//   %and = and i32 %x, %y
+//   %cond = select i1 %or0, i32 %and, i32 %or
+//   ret i32 %cond
+//
+// Expect:
+//   %or = or i32 %x, %y
+//   ret i32 %or
+//
+// We could know what bit was enabled for %x, %y by ICmpInst in SelectInst.
+static Instruction *foldSelectICmpBinOp(SelectInst &SI, ICmpInst *ICI,
+                                        Value *CmpLHS, Value *CmpRHS,
+                                        Value *TVal, Value *FVal,
+                                        InstCombinerImpl &IC) {
+  Value *X, *Y;
+  const APInt *C;
+  unsigned CmpLHSOpc;
+  bool IsDisjoint = false;
+  // Specially handling for X^Y==0 transformed to X==Y
+  if (match(TVal, m_c_BitwiseLogic(m_Specific(CmpLHS), m_Specific(CmpRHS)))) {
+    X = CmpLHS;
+    Y = CmpRHS;
+    APInt ZeroVal = APInt::getZero(CmpLHS->getType()->getScalarSizeInBits());
+    C = const_cast<APInt *>(&ZeroVal);
+    CmpLHSOpc = Instruction::Xor;
+  } else if ((match(CmpLHS, m_BinOp(m_Value(X), m_Value(Y))) &&
+              match(CmpRHS, m_APInt(C))) &&
+             (match(TVal, m_c_BinOp(m_Specific(X), m_Value())) ||
+              match(TVal, m_c_BinOp(m_Specific(Y), m_Value())))) {
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goldsteinn wrote:

afaict, these should only be matching bitwise logic

https://github.com/llvm/llvm-project/pull/91762