[llvm] [Attributor] Change allocation size and load/store offsets using AAPointerInfo for Alloca instructions and keep track of instructions causing an Access (PR #72029)

[Shilei Tian via llvm-commits]

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@@ -13451,41 +13701,124 @@ struct AAAllocationInfoImpl : public AAAllocationInfo {
     if (!AllocationSize)
       return indicatePessimisticFixpoint();
 
-    // For zero sized allocations, we give up.
-    // Since we can't reduce further
+    // For zero sized allocations, we give up
+    // because we cannot reduce them any further.
     if (*AllocationSize == 0)
       return indicatePessimisticFixpoint();
 
-    int64_t BinSize = PI->numOffsetBins();
-
-    // TODO: implement for multiple bins
-    if (BinSize > 1)
-      return indicatePessimisticFixpoint();
-
-    if (BinSize == 0) {
-      auto NewAllocationSize = std::make_optional<TypeSize>(0, false);
+    int64_t NumBins = PI->numOffsetBins();
+    if (NumBins == 0) {
+      std::optional<TypeSize> NewAllocationSize =
+          std::optional<TypeSize>(TypeSize(0, false));
       if (!changeAllocationSize(NewAllocationSize))
         return ChangeStatus::UNCHANGED;
       return ChangeStatus::CHANGED;
     }
 
-    // TODO: refactor this to be part of multiple bin case
-    const auto &It = PI->begin();
+    // Algorithm:
+    // For all the accessed ranges in AAPointerInfo, we need to find the minimum
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shiltian wrote:

I'm not sure I understand this part completely. Some extra explanation would be more helpful. But did you consider alignment/padding here?

https://github.com/llvm/llvm-project/pull/72029