[llvm] [LLVM][AArch64]Use load/store with consecutive registers in SME2 or S… (PR #77665)

[Momchil Velikov via llvm-commits]

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@@ -3037,19 +3055,37 @@ bool AArch64FrameLowering::spillCalleeSavedRegisters(
       std::swap(Reg1, Reg2);
       std::swap(FrameIdxReg1, FrameIdxReg2);
     }
+
+    unsigned PnReg;
+    unsigned PairRegs;
+    if (RPI.isPaired() && RPI.isScalable()) {
+      PnReg = findFreePredicateAsCounterReg(MF);
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momchil-velikov wrote:

We need just one register, so there's no need to call the function every time, at the time of the creation of the `ptrue` instruction is enough. That'll also defend against the function returning different registers on each iteration (once we get a register and used in `ptrue` it's not free anymore, is it?).

https://github.com/llvm/llvm-project/pull/77665