[llvm] [SelectionDAG] Use unaligned store/load to move AVX registers onto stack for `insertelement` (PR #82130)

[Manish Kausik H via llvm-commits]

================
@@ -363,6 +363,19 @@ SDValue SelectionDAGLegalize::ExpandConstant(ConstantSDNode *CP) {
   return Result;
 }
 
+// Helper function that generates an MMO that considers the alignment of the
+// stack, and the size of the stack object
+static MachineMemOperand *getStackAlignedMMO(SDValue StackPtr,
+                                             MachineFunction &MF,
+                                             bool isObjectScalable) {
+  auto &MFI = MF.getFrameInfo();
+  int FI = cast<FrameIndexSDNode>(StackPtr)->getIndex();
+  MachinePointerInfo PtrInfo = MachinePointerInfo::getFixedStack(MF, FI);
+  uint64_t ObjectSize = isObjectScalable ? ~UINT64_C(0) : MFI.getObjectSize(FI);
+  return MF.getMachineMemOperand(PtrInfo, MachineMemOperand::MOStore,
+                                 ObjectSize, MFI.getObjectAlign(FI));
+}
----------------
Nirhar wrote:

Separated this into a different PR: https://github.com/llvm/llvm-project/pull/82171

https://github.com/llvm/llvm-project/pull/82130