[llvm] [CGData] Global Merge Functions (PR #112671)

[Zhaoxuan Jiang via llvm-commits]

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@@ -117,7 +149,38 @@ static void removeIdenticalIndexPair(
       SF->IndexOperandHashMap->erase(Pair);
 }
 
-void StableFunctionMap::finalize() {
+static bool isProfitable(
+    const SmallVector<std::unique_ptr<StableFunctionMap::StableFunctionEntry>>
+        &SFS) {
+  unsigned StableFunctionCount = SFS.size();
+  if (StableFunctionCount < GlobalMergingMinMerges)
+    return false;
+
+  unsigned InstCount = SFS[0]->InstCount;
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nocchijiang wrote:

The number of IR cannot precisely reflect the actual number of machine instructions (often the latter is larger for AArch64. Take the access of a global value for example, it will be expanded into an `ADRP` pair for small code model), which results in `Benefit` underestimated and some profitable merging opportunities dropped. I am not sure if there is existing code that could be reused to better estimate the machine instruction count, but at least we may introduce a multiplier on `InstCount` for fine-tuning of the behavior.

https://github.com/llvm/llvm-project/pull/112671