[llvm] [LV][EVL] Attach a new metadata on EVL vectorized loops (PR #131000)

[Pengcheng Wang via llvm-commits]

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@@ -7828,6 +7828,26 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
 
       LoopVectorizeHints Hints(L, true, *ORE);
       Hints.setAlreadyVectorized();
+
+      // Check if it's EVL-vectorized and mark the corresponding metadata.
+      bool IsEVLVectorized =
+          llvm::any_of(*HeaderVPBB, [](const VPRecipeBase &Recipe) {
+            // Looking for the ExplictVectorLength VPInstruction.
+            if (const auto *VI = dyn_cast<VPInstruction>(&Recipe))
+              return VI->getOpcode() == VPInstruction::ExplicitVectorLength;
+            return false;
+          });
+      if (IsEVLVectorized) {
+        LLVMContext &Context = L->getHeader()->getContext();
+        MDNode *LoopID = L->getLoopID();
+        auto *IsEVLVectorizedMD = MDNode::get(
+            Context,
+            {MDString::get(Context, "llvm.loop.isvectorized.tailfoldingstyle"),
+             MDString::get(Context, "evl")});
+        MDNode *NewLoopID = makePostTransformationMetadata(Context, LoopID, {},
+                                                           {IsEVLVectorizedMD});
+        L->setLoopID(NewLoopID);
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wangpc-pp wrote:

Non-blocking: is it required to change the LoopID since we are just simply attaching a new metadata? This is not a transformation.

https://github.com/llvm/llvm-project/pull/131000