[llvm] [AArch64][SVE] Pair SVE fill/spill into LDP/STP with -msve-vector-bits=128. (PR #134068)

[Paul Walker via llvm-commits]

================
@@ -2840,6 +2883,9 @@ bool AArch64LoadStoreOpt::optimizeBlock(MachineBasicBlock &MBB,
     updateDefinedRegisters(*MBBI, DefinedInBB, TRI);
     if (TII->isPairableLdStInst(*MBBI) && tryToPairLdStInst(MBBI))
       Modified = true;
+    else if (CanPairFillSpill && isPairableFillSpillInst(*MBBI) &&
+             tryToPairLdStInst(MBBI))
+      Modified = true;
----------------
paulwalker-arm wrote:

It's worth trying.  I wasn't thinking of extending `isPairableLdStInst` specifically but wondered if the extra checks can be pushing into the `tryTo..` function or perhaps `isCandidateToMergeOrPair`.

https://github.com/llvm/llvm-project/pull/134068