[llvm] [LoongArch] Add patterns for vstelm instructions (PR #139201)

[Lu Weining via llvm-commits]

================
@@ -140,7 +140,36 @@ bool LoongArchRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
 
   bool FrameRegIsKill = false;
 
-  if (!isInt<12>(Offset.getFixed())) {
+  int fixed_offset = Offset.getFixed();
+  bool OffsetLegal = false;
+
+  // Handle offsets that exceed the immediate range of the instruction
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SixWeining wrote:

```suggestion
  // Handle offsets that exceed the immediate range of the instruction.
```

https://github.com/llvm/llvm-project/pull/139201