[llvm] [RISCV] Select Zvkb VANDN for shorter constant loading sequences (PR #123345)

[Craig Topper via llvm-commits]

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@@ -3224,8 +3224,25 @@ bool RISCVDAGToDAGISel::selectInvLogicImm(SDValue N, SDValue &Val) {
 
   // Abandon this transform if the constant is needed elsewhere.
   for (const SDNode *U : N->users()) {
-    if (!ISD::isBitwiseLogicOp(U->getOpcode()))
+    switch (U->getOpcode()) {
+    case ISD::AND:
+    case ISD::OR:
+    case ISD::XOR:
+      if (!(Subtarget->hasStdExtZbb() || Subtarget->hasStdExtZbkb()))
+        return false;
+      break;
+    case RISCVISD::VMV_V_X_VL:
+      if (!Subtarget->hasStdExtZvkb())
+        return false;
+      if (!all_of(U->users(), [](const SDNode *V) {
+            return V->getOpcode() == ISD::AND ||
+                   V->getOpcode() == RISCVISD::AND_VL;
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topperc wrote:

ISD::AND doesn't have a passthru. For RISCV::AND_VL you would need to loop through `U->uses()` instead of `U->users()`. That will give you an `SDUse &`. From there you can call `SDUse::getUser()` to get `V` and `SDUse::getOperandNo` to get the operand number of the use. The passthru will be operand 2.

https://github.com/llvm/llvm-project/pull/123345