[llvm] [VPlan] Hoist loads with invariant addresses using noalias metadata. (PR #166247)

[via llvm-commits]

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@@ -3914,6 +3920,54 @@ void VPlanTransforms::materializeBroadcasts(VPlan &Plan) {
   }
 }
 
+void VPlanTransforms::hoistInvariantLoads(VPlan &Plan) {
+  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
+
+  // Collect candidate loads with invariant addresses and noalias scopes
+  // metadata and memory-writing recipes with noalias metadata.
+  SmallVector<std::pair<VPRecipeBase *, MemoryLocation>> CandidateLoads;
+  SmallVector<MemoryLocation> Stores;
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(LoopRegion->getEntry()))) {
+    for (VPRecipeBase &R : *VPBB) {
+      // Only handle single-scalar replicated loads with invariant addresses.
+      if (auto *RepR = dyn_cast<VPReplicateRecipe>(&R)) {
+        if (RepR->isPredicated() || !RepR->isSingleScalar() ||
+            RepR->getOpcode() != Instruction::Load)
+          continue;
+
+        VPValue *Addr = RepR->getOperand(0);
+        if (Addr->isDefinedOutsideLoopRegions()) {
+          MemoryLocation Loc = *vputils::getMemoryLocation(*RepR);
+          if (!Loc.AATags.Scope)
+            continue;
+          CandidateLoads.push_back({RepR, Loc});
+        }
+      }
+      if (R.mayWriteToMemory()) {
+        auto Loc = vputils::getMemoryLocation(R);
+        if (!Loc || !Loc->AATags.Scope || !Loc->AATags.NoAlias)
+          return;
+        Stores.push_back(*Loc);
+      }
+    }
+  }
+
+  VPBasicBlock *Preheader = Plan.getVectorPreheader();
+  for (auto &[LoadRecipe, LoadLoc] : CandidateLoads) {
+    // Hoist the load to the preheader if it doesn't alias with any stores
+    // according to the noalias metadata. Other loads should have been hoisted
+    // by other passes
----------------
ayalz wrote:

```suggestion
    // by other passes.
```

https://github.com/llvm/llvm-project/pull/166247