[llvm] [LLVM][CodeGen] Remove failure cases when widening EXTRACT/INSERT_SUBVECTOR. (PR #162308)

[Paul Walker via llvm-commits]

================
@@ -7471,17 +7491,52 @@ SDValue DAGTypeLegalizer::WidenVecOp_INSERT_SUBVECTOR(SDNode *N) {
     }
   }
 
+  if (!IndicesValid)
+    report_fatal_error(
+        "Don't know how to widen the operands for INSERT_SUBVECTOR");
+
   SDLoc DL(N);
 
   // We need to make sure that the indices are still valid, otherwise we might
   // widen what was previously well-defined to something undefined.
-  if (IndicesValid && InVec.isUndef() && N->getConstantOperandVal(2) == 0)
+  if (InVec.isUndef() && N->getConstantOperandVal(2) == 0)
     return DAG.getNode(ISD::INSERT_SUBVECTOR, DL, VT, InVec, SubVec,
                        N->getOperand(2));
 
-  if (!IndicesValid || OrigVT.isScalableVector())
-    report_fatal_error(
-        "Don't know how to widen the operands for INSERT_SUBVECTOR");
+  if (OrigVT.isScalableVector()) {
+    // Fallback to inserting through memory.
+
+    Align Alignment = DAG.getReducedAlign(VT, /*UseABI=*/false);
+    SDValue StackPtr = DAG.CreateStackTemporary(VT.getStoreSize(), Alignment);
+    auto &MF = DAG.getMachineFunction();
+    auto FrameIndex = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
+    auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FrameIndex);
+
+    MachineMemOperand *StoreMMO = DAG.getMachineFunction().getMachineMemOperand(
+        PtrInfo, MachineMemOperand::MOStore,
+        LocationSize::beforeOrAfterPointer(), Alignment);
+    MachineMemOperand *LoadMMO = DAG.getMachineFunction().getMachineMemOperand(
+        PtrInfo, MachineMemOperand::MOLoad,
+        LocationSize::beforeOrAfterPointer(), Alignment);
+
+    // Write out the vector being inserting into.
+    SDValue Ch =
+        DAG.getStore(DAG.getEntryNode(), DL, InVec, StackPtr, StoreMMO);
+
+    // Build a mask to match the length of the sub-vector.
+    SDValue Mask =
+        DAG.getMaskFromElementCount(DL, SubVT, OrigVT.getVectorElementCount());
+
+    // Overwrite the sub-vector at the required offset.
+    StackPtr =
+        TLI.getVectorSubVecPointer(DAG, StackPtr, VT, OrigVT, N->getOperand(2));
+    Ch = DAG.getMaskedStore(Ch, DL, SubVec, StackPtr,
+                            DAG.getUNDEF(StackPtr.getValueType()), Mask, VT,
+                            StoreMMO, ISD::UNINDEXED, ISD::NON_EXTLOAD);
+
+    // Read back the result.
+    return DAG.getLoad(VT, DL, Ch, StackPtr, LoadMMO);
----------------
paulwalker-arm wrote:

Ouch. Thanks for spotting. I've updated to use a dedicated variable for the sub-vector address.

https://github.com/llvm/llvm-project/pull/162308