[llvm] [IR] Allow non-constant offsets in @llvm.vector.splice.{left,right} (PR #174693)

[Luke Lau via llvm-commits]

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@@ -12029,27 +12030,20 @@ SDValue TargetLowering::expandVectorSplice(SDNode *Node,
   SDValue StackPtr2 = DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr, VTBytes);
   SDValue StoreV2 = DAG.getStore(StoreV1, DL, V2, StackPtr2, PtrInfo);
 
-  if (Node->getOpcode() == ISD::VECTOR_SPLICE_LEFT) {
-    // Load back the required element. getVectorElementPointer takes care of
-    // clamping the index if it's out-of-bounds.
-    StackPtr = getVectorElementPointer(DAG, StackPtr, VT, Node->getOperand(2));
-    // Load the spliced result
-    return DAG.getLoad(VT, DL, StoreV2, StackPtr,
-                       MachinePointerInfo::getUnknownStack(MF));
-  }
-
-  // NOTE: TrailingElts must be clamped so as not to read outside of V1:V2.
-  TypeSize EltByteSize = VT.getVectorElementType().getStoreSize();
-  SDValue TrailingBytes = DAG.getConstant(Imm * EltByteSize, DL, PtrVT);
+  // NOTE: TrailingBytes must be clamped so as not to read outside of V1:V2.
+  SDValue EltByteSize =
+      DAG.getTypeSize(DL, PtrVT, VT.getVectorElementType().getStoreSize());
+  SDValue TrailingBytes = DAG.getNode(ISD::MUL, DL, PtrVT, Offset, EltByteSize);
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lukel97 wrote:

Added an extend in b5c7edd4afc505a27f38070d3c40742709aa2e0c, I think it just happened to work beforehand because Offset is cast to getVectorIdxTy in SelectionDAGBuilder

https://github.com/llvm/llvm-project/pull/174693