[llvm] [DAG] Generalize setcc(setcc) fold to use known bits. (PR #66503)

[Craig Topper via llvm-commits]

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@@ -4652,21 +4652,25 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
                           DAG.getConstant(C1 & Imm, dl, ExtDstTy), Cond);
     } else if ((N1C->isZero() || N1C->isOne()) &&
                (Cond == ISD::SETEQ || Cond == ISD::SETNE)) {
-      // SETCC (SETCC), [0|1], [EQ|NE]  -> SETCC
-      if (N0.getOpcode() == ISD::SETCC &&
+      // SETCC (X), [0|1], [EQ|NE]  -> X if X is known 0/1
+      if ((N0.getOpcode() == ISD::SETCC || VT != MVT::i1) &&
           isTypeLegal(VT) && VT.bitsLE(N0.getValueType()) &&
           (N0.getValueType() == MVT::i1 ||
-           getBooleanContents(N0.getOperand(0).getValueType()) ==
-                       ZeroOrOneBooleanContent)) {
+           getBooleanContents(N0.getValueType()) == ZeroOrOneBooleanContent) &&
+          DAG.MaskedValueIsZero(
+              N0, APInt::getHighBitsSet(N0.getValueSizeInBits(),
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topperc wrote:

APInt::getBitsSetFrom(N0.getValueSizeInBits(), 1)

https://github.com/llvm/llvm-project/pull/66503