[llvm] [RISCV] Lower (select c, y, 0) -> (qc.muliadd c, y-1) (PR #190323)

[Craig Topper via llvm-commits]

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@@ -9663,8 +9663,14 @@ static SDValue lowerSelectToBinOp(SDNode *N, SelectionDAG &DAG,
       return DAG.getNode(ISD::AND, DL, VT, Neg, DAG.getFreeze(FalseV));
     }
     if (isNullConstant(FalseV)) {
-      // (select c, (1 << ShAmount) + 1, 0) -> (c << ShAmount) + c
       if (auto *TrueC = dyn_cast<ConstantSDNode>(TrueV)) {
+        // (select c, y, 0) -> (c * (y - 1)) + c
+        int64_t TrueM2 = TrueC->getSExtValue() - 1;
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topperc wrote:

If TrueC is INT64_MIN, this has signed overflow which would fail if the compiler was built with UBSAN. Since the code is before the check for hasVendorXqciac we can't rely on the type being i32 to protect it.

https://github.com/llvm/llvm-project/pull/190323