[llvm] [X86] Fold ADC(SHL(X, 1), 0, Carry) to ADC(X, X, Carry) (PR #219512)

[Simon Pilgrim via llvm-commits]

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@@ -59829,6 +59829,13 @@ static SDValue combineADC(SDNode *N, SelectionDAG &DAG,
     return DAG.getNode(X86ISD::ADC, SDLoc(N), N->getVTList(), LHS.getOperand(0),
                        LHS.getOperand(1), CarryIn);
 
+  // Fold ADC(SHL(X,1),0,Carry) -> ADC(X,X,Carry)
+  // iff the flag result is dead.
+  if (LHS.getOpcode() == ISD::SHL && isOneConstant(LHS.getOperand(1)) && RHSC &&
+      RHSC->isZero() && !needCarryOrOverflowFlag(SDValue(N, 1)))
+    return DAG.getNode(X86ISD::ADC, SDLoc(N), N->getVTList(), LHS.getOperand(0),
+                       LHS.getOperand(0), CarryIn);
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RKSimon wrote:

freeze LHS.getOperand(0) as we're increasing usage

https://github.com/llvm/llvm-project/pull/219512