[llvm] Add option to dump IR to files instead of stderr (PR #66412)

[Nuri Amari via llvm-commits]

================
@@ -46,6 +46,24 @@ class PrintIRInstrumentation {
   void registerCallbacks(PassInstrumentationCallbacks &PIC);
 
 private:
+  enum class SuffixType {
+    Before,
+    After,
+    Invalidated,
+  };
+
+  struct PassRunDescriptor {
+    const Module *M;
+    SmallString<128> DumpIRFilename;
----------------
NuriAmari wrote:

I did this because I use structural binding to unpack the struct, and there doesn't seem a way to have the unpacked members lose the const qualifier. I need to modify DumpIRFilename to append the suffix and I don't want to copy it unnecessarily.

```cpp
auto [M, DumpIRFilename, IRName, StoredPassID] = popPassRunDescriptor(PassID);
```

I'll just unpack the struct normally -- perhaps I got a little too excited about using structural binding.

https://github.com/llvm/llvm-project/pull/66412