[llvm] [GenericCycle] Add a Cache for getExitBlocks in GenericCycle (PR #112290)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-adt

Author: Chengjun (Chengjunp)

<details>
<summary>Changes</summary>

In `UniformityAnalysis`, we need to get the exit blocks of cycles in the `DivergencePropagator` and currently, we have to do a search for the exit blocks every time. In this change, we add a cache of the results in the `GenericCycle` so that it can save the compile time. By testing, for some large cases, this can save about 60% compile time in the `UniformityAnalysis`.

---
Full diff: https://github.com/llvm/llvm-project/pull/112290.diff


2 Files Affected:

- (modified) llvm/include/llvm/ADT/GenericCycleImpl.h (+6) 
- (modified) llvm/include/llvm/ADT/GenericCycleInfo.h (+6-1) 


``````````diff
diff --git a/llvm/include/llvm/ADT/GenericCycleImpl.h b/llvm/include/llvm/ADT/GenericCycleImpl.h
index 3d2c5f42883558..ee7296043dce73 100644
--- a/llvm/include/llvm/ADT/GenericCycleImpl.h
+++ b/llvm/include/llvm/ADT/GenericCycleImpl.h
@@ -47,6 +47,11 @@ bool GenericCycle<ContextT>::contains(const GenericCycle *C) const {
 template <typename ContextT>
 void GenericCycle<ContextT>::getExitBlocks(
     SmallVectorImpl<BlockT *> &TmpStorage) const {
+  if (!ExitBlocksCache->empty()) {
+    TmpStorage = *ExitBlocksCache;
+    return;
+  }
+
   TmpStorage.clear();
 
   size_t NumExitBlocks = 0;
@@ -65,6 +70,7 @@ void GenericCycle<ContextT>::getExitBlocks(
 
     TmpStorage.resize(NumExitBlocks);
   }
+  ExitBlocksCache->append(TmpStorage.begin(), TmpStorage.end());
 }
 
 template <typename ContextT>
diff --git a/llvm/include/llvm/ADT/GenericCycleInfo.h b/llvm/include/llvm/ADT/GenericCycleInfo.h
index 8c2fa0490e638a..98d935975cc373 100644
--- a/llvm/include/llvm/ADT/GenericCycleInfo.h
+++ b/llvm/include/llvm/ADT/GenericCycleInfo.h
@@ -74,12 +74,16 @@ template <typename ContextT> class GenericCycle {
   ///       always have the same depth.
   unsigned Depth = 0;
 
+  /// Cache for the results of GetExitBlocks
+  std::unique_ptr<SmallVector<BlockT *, 4>> ExitBlocksCache;
+
   void clear() {
     Entries.clear();
     Children.clear();
     Blocks.clear();
     Depth = 0;
     ParentCycle = nullptr;
+    ExitBlocksCache->clear();
   }
 
   void appendEntry(BlockT *Block) { Entries.push_back(Block); }
@@ -91,7 +95,8 @@ template <typename ContextT> class GenericCycle {
   GenericCycle &operator=(GenericCycle &&Rhs) = delete;
 
 public:
-  GenericCycle() = default;
+  GenericCycle()
+      : ExitBlocksCache(std::make_unique<SmallVector<BlockT *, 4>>()){};
 
   /// \brief Whether the cycle is a natural loop.
   bool isReducible() const { return Entries.size() == 1; }

``````````

</details>


https://github.com/llvm/llvm-project/pull/112290