[AArch64][SVE] Fix epilogue for SVE when the stack is realigned.

While deallocating the stackframe, the offset used to reload the
callee-saved registers was not pointing to the SVE callee-saves,
but rather to the whole SVE area.

   +--------------+
   | GRP callee   |
   |     saves    |
   +--------------+ <- FP
   | SVE callee   |
   |     saves    |
   +--------------+ <- Should restore SVE callee saves from here
   |  SVE Spills  |
   |  and Locals  |
   +--------------+ <- instead of from here.
   |              |
   :              :
   |              |
   +--------------+ <- SP

Reviewed By: paulwalker-arm

Differential Revision: https://reviews.llvm.org/D84539

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -1596,12 +1596,13 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
   // Deallocate the SVE area.
   if (SVEStackSize) {
     if (AFI->isStackRealigned()) {
-      if (AFI->getSVECalleeSavedStackSize())
-        // Set SP to start of SVE area, from which the callee-save reloads
-        // can be done. The code below will deallocate the stack space
+      if (int64_t CalleeSavedSize = AFI->getSVECalleeSavedStackSize())
+        // Set SP to start of SVE callee-save area from which they can
+        // be reloaded. The code below will deallocate the stack space
         // space by moving FP -> SP.
         emitFrameOffset(MBB, RestoreBegin, DL, AArch64::SP, AArch64::FP,
-                        -SVEStackSize, TII, MachineInstr::FrameDestroy);
+                        {-CalleeSavedSize, MVT::nxv1i8}, TII,
+                        MachineInstr::FrameDestroy);
     } else {
       if (AFI->getSVECalleeSavedStackSize()) {
         // Deallocate the non-SVE locals first before we can deallocate (and

llvm/test/CodeGen/AArch64/framelayout-sve.mir

@@ -500,7 +500,7 @@ body:             |
 # CHECK-NEXT: $[[TMP:x[0-9]+]] = frame-setup SUBXri $sp, 16, 0
 # CHECK-NEXT: $sp = ANDXri killed $[[TMP]]
 
-# CHECK:      $sp = frame-destroy ADDVL_XXI $fp, -19
+# CHECK:      $sp = frame-destroy ADDVL_XXI $fp, -18
 # CHECK-NEXT: $p15 = frame-destroy LDR_PXI $sp, 4
 # CHECK-NEXT: $p14 = frame-destroy LDR_PXI $sp, 5
 # CHECK:      $p5 = frame-destroy LDR_PXI $sp, 14