Backport aarch64 SVE compile fix from upstream

From Brad, ok kettenis@

gnu/llvm/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -2471,6 +2471,19 @@ MVT AArch64TargetLowering::getScalarShiftAmountTy(const DataLayout &DL,
 bool AArch64TargetLowering::allowsMisalignedMemoryAccesses(
     EVT VT, unsigned AddrSpace, Align Alignment, MachineMemOperand::Flags Flags,
     unsigned *Fast) const {
+
+   // Allow SVE loads/stores where the alignment >= the size of the element type,
+   // even with +strict-align. Predicated SVE loads/stores (e.g. ld1/st1), used
+   // for stores that come from IR, only require element-size alignment (even if
+   // unaligned accesses are disabled). Without this, these will be forced to
+   // have 16-byte alignment with +strict-align (and fail to lower as we don't
+   // yet support TLI.expandUnalignedLoad() and TLI.expandUnalignedStore()).
+   if (VT.isScalableVector()) {
+     unsigned ElementSizeBits = VT.getScalarSizeInBits();
+     if (ElementSizeBits % 8 == 0 && Alignment >= Align(ElementSizeBits / 8))
+       return true;
+   }
+
   if (Subtarget->requiresStrictAlign())
     return false;