[llvm] [TableGen] Integrate TableGen-based macro fusion (PR #73115)

[Matt Arsenault via llvm-commits]

================
@@ -323,6 +324,12 @@ class TargetSubtargetInfo : public MCSubtargetInfo {
   /// helps removing redundant copies generated by register allocator when
   /// handling complex eviction chains.
   virtual bool enableSpillageCopyElimination() const { return false; }
+
+  /// Enable macro fusion for this subtarget.
+  virtual bool enableMacroFusion() const { return false; }
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arsenm wrote:

Where is the use context where enableMacroFusion is necessary? I assume the use just directly iterates through the returned instances from getMacroFusions. That is, with something like:

```
if (enableMacroFusion()) 
  doStuff(getMacroFusions()) 

```

there's no point in having enableMacroFusion at all



https://github.com/llvm/llvm-project/pull/73115