[llvm] [TailRecElim] Introduce support for shift accumulator optimization (PR #181331)

[Antonio Frighetto via llvm-commits]

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@@ -436,6 +524,10 @@ class TailRecursionEliminator {
   // The instruction doing the accumulating.
   Instruction *AccumulatorRecursionInstr = nullptr;
 
+  // The base case return value. It exists only if the accumulator
+  // operation is pseudo-associative.
+  Constant *AccumulatorInitialValue = nullptr;
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antoniofrighetto wrote:

```suggestion
  Constant *AccumulatorInitialValue = nullptr;
```

https://github.com/llvm/llvm-project/pull/181331