[llvm] [PowerPC] Implement a more efficient memcmp in cases where the length is known. (PR #158657)

[Lei Huang via llvm-commits]

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@@ -15556,6 +15556,63 @@ SDValue PPCTargetLowering::combineSetCC(SDNode *N,
       SDValue Add = DAG.getNode(ISD::ADD, DL, OpVT, LHS, RHS.getOperand(1));
       return DAG.getSetCC(DL, VT, Add, DAG.getConstant(0, DL, OpVT), CC);
     }
+    if (Subtarget.hasVSX()) {
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lei137 wrote:

Please add a documentation as to the type of optimization that is being done in this block.

https://github.com/llvm/llvm-project/pull/158657