[NFC][RISCV] Add test for scalable offset under large stack size.

[HsiangKai]

Summary

This test case shows that we access wrong stack slots when the frame object has scalable offset under large stack size.

[rogfer01]

LGTM

llvm/test/CodeGen/RISCV/rvv/addi-scalable-offset.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=riscv64 -stop-after=prologepilog %s -o - 2>&1 | FileCheck %s
+
+--- |
+  define void @add_scalable_offset(
+            <vscale x 1 x i64> *%pa,
+            i64 %vl)
+  {
+    ret void
+  }
+...
+---
+name: add_scalable_offset
+tracksRegLiveness: true
+frameInfo:
+  isFrameAddressTaken: true
+  stackSize:       2240
+stack:
+  - { id: 0, type: default, offset: 0, size: 1120, alignment: 4,
+      stack-id: default }
+  - { id: 1, type: default, offset: 1120, size: 1120, alignment: 4,
+      stack-id: default }
+  - { id: 2, offset: 0, size: 8, alignment: 8, stack-id: scalable-vector }
+body: |
+  bb.0:
+    liveins: $x10, $x11
+
+    ; CHECK-LABEL: name: add_scalable_offset
+    ; CHECK: liveins: $x10, $x11, $x1
+    ; CHECK: $x2 = frame-setup ADDI $x2, -2032
+    ; CHECK: CFI_INSTRUCTION def_cfa_offset 2032
+    ; CHECK: SD killed $x1, $x2, 2024 :: (store 8 into %stack.3)
+    ; CHECK: SD killed $x8, $x2, 2016 :: (store 8 into %stack.4)
+    ; CHECK: CFI_INSTRUCTION offset $x1, -8
+    ; CHECK: CFI_INSTRUCTION offset $x8, -16
+    ; CHECK: $x8 = frame-setup ADDI $x2, 2032
+    ; CHECK: CFI_INSTRUCTION def_cfa $x8, 0
+    ; CHECK: $x2 = frame-setup ADDI $x2, -240
+    ; CHECK: $x12 = PseudoReadVLENB
+    ; CHECK: $x2 = SUB $x2, killed $x12
+    ; CHECK: dead renamable $x11 = PseudoVSETVLI killed renamable $x11, 88, implicit-def $vl, implicit-def $vtype
+    ; CHECK: renamable $v25 = PseudoVLE64_V_M1 killed renamable $x10, $noreg, 64, implicit $vl, implicit $vtype :: (load unknown-size from %ir.pa, align 8)
+    ; CHECK: $x10 = LUI 1048575
+    ; CHECK: $x10 = ADDIW killed $x10, 1824
+    ; CHECK: $x10 = ADD $x8, killed $x10
+    ; CHECK: VS1R_V killed renamable $v25, killed renamable $x10
+    ; CHECK: $x10 = PseudoReadVLENB
+    ; CHECK: $x2 = ADD $x2, killed $x10
+    ; CHECK: $x2 = frame-destroy ADDI $x2, 240
+    ; CHECK: $x8 = LD $x2, 2016 :: (load 8 from %stack.4)
+    ; CHECK: $x1 = LD $x2, 2024 :: (load 8 from %stack.3)
+    ; CHECK: $x2 = frame-destroy ADDI $x2, 2032
+    ; CHECK: PseudoRET
+    %1:gpr = COPY $x11
+    %0:gpr = COPY $x10
+    %2:vr = PseudoVLE64_V_M1 %0, %1, 64, implicit $vl, implicit $vtype :: (load unknown-size from %ir.pa, align 8)
+    %3:gpr = ADDI %stack.2, 0
+    VS1R_V killed %2:vr, %3:gpr
+    PseudoRET
+
+...