[llvm] [LoopPeel] Peel last iteration to enable load widening (PR #173420)

[Florian Hahn via llvm-commits]

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@@ -890,6 +1049,76 @@ void llvm::computePeelCount(Loop *L, unsigned LoopSize,
   }
 }
 
+bool llvm::widenLoadsAfterPeel(Loop &L, ScalarEvolution &SE,
+                               const DataLayout &DL,
+                               const TargetTransformInfo &TTI,
+                               DominatorTree &DT) {
+  BasicBlock *Latch = L.getLoopLatch();
+  if (!Latch)
+    return false;
+
+  bool Changed = false;
+
+  for (BasicBlock *BB : L.blocks()) {
+    if (!DT.dominates(BB, Latch))
+      continue;
+    SmallVector<LoadGroup> Groups =
+        findLoadGroupsForWidening(BB, L, SE, DL, TTI);
+    for (const LoadGroup &Group : Groups) {
+      LoadInst *InsertPoint = Group.FirstLoad;
+      IRBuilder<> Builder(InsertPoint);
+      Value *BasePtr = Group.BasePtr;
+      int64_t FirstOffset = Group.Loads[0].second.getSExtValue();
+      // If the first load doesn't start at offset 0, we need to adjust.
+      if (FirstOffset != 0) {
+        Value *OrigPtr = Group.BasePtr;
+        BasePtr = Builder.CreatePtrAdd(
+            OrigPtr,
+            ConstantInt::get(
+                Builder.getIndexTy(DL, DL.getDefaultGlobalsAddressSpace()),
+                FirstOffset));
+      }
+      // Merge AA metadata from all loads.
+      AAMDNodes AATags = InsertPoint->getAAMetadata();
+      for (const auto &[Load, Offset] : Group.Loads) {
+        if (Load != InsertPoint)
+          AATags = AATags.concat(Load->getAAMetadata());
+      }
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fhahn wrote:

Shouldn't this be the union? Needs test

https://github.com/llvm/llvm-project/pull/173420