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

[Matt Arsenault via llvm-commits]

================
@@ -6201,8 +6201,33 @@ SDValue DAGTypeLegalizer::WidenVecRes_EXTRACT_SUBVECTOR(SDNode *N) {
       return DAG.getNode(ISD::CONCAT_VECTORS, dl, WidenVT, Parts);
     }
 
-    report_fatal_error("Don't know how to widen the result of "
-                       "EXTRACT_SUBVECTOR for scalable vectors");
+    // Fallback to extracting through memory.
+
+    Align Alignment = DAG.getReducedAlign(InVT, /*UseABI=*/false);
+    SDValue StackPtr = DAG.CreateStackTemporary(InVT.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(
----------------
arsenm wrote:

```suggestion
    MachineMemOperand *StoreMMO = MF.getMachineMemOperand(
        PtrInfo, MachineMemOperand::MOStore,
        LocationSize::beforeOrAfterPointer(), Alignment);
    MachineMemOperand *LoadMMO = MF.getMachineMemOperand(
```

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