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

[Matt Arsenault via llvm-commits]

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@@ -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:

But you're just avoiding the creation of an empty vector, which doesn't matter. I would just do
vector Mutations = ST.getMacroFusions()
if (!Mutations.empty())
  DAG->addMutation(createMacroFusion(std::move(Mutations))




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