[llvm] [SLP] no need to generate extract for in-tree uses for original scala… (PR #76077)

[Alexey Bataev via llvm-commits]

================
@@ -11898,6 +11864,12 @@ Value *BoUpSLP::vectorizeTree(
     Value *Vec = E->VectorizedValue;
     assert(Vec && "Can't find vectorizable value");
 
+    // Generate extract for in-tree uses if the use is scalar operand in
+    // vectorized instruction.
+    if (auto *UserVecTE = getTreeEntry(User))
+      if (doesInTreeUserNeedToExtract(Scalar, cast<Instruction>(User), TLI))
+        User = cast<llvm::User>(UserVecTE->VectorizedValue);
+
----------------
alexey-bataev wrote:

Ok, I see why you need this.
Instead, I suggest another approach. When building the external uses entry for such scalars, just mark that there is no exact user. In this case all uses of this scalar will be automatically replaced by extractelement and you don't need this change anymore.
But I think some adjustment in the original code for also should be done.
```
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index 5c325ad8a291..e66e2a7d110e 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -4928,33 +4928,33 @@ void BoUpSLP::buildExternalUses(
         if (!UserInst)
           continue;

-        if (isDeleted(UserInst))
-          continue;
-
         // Skip in-tree scalars that become vectors
         if (TreeEntry *UseEntry = getTreeEntry(U)) {
-          Value *UseScalar = UseEntry->Scalars[0];
           // Some in-tree scalars will remain as scalar in vectorized
-          // instructions. If that is the case, the one in Lane 0 will
+          // instructions. If that is the case, the one in FoundLane will
           // be used.
-          if (UseScalar != U ||
-              UseEntry->State == TreeEntry::ScatterVectorize ||
+          if (UseEntry->State == TreeEntry::ScatterVectorize ||
               UseEntry->State == TreeEntry::PossibleStridedVectorize ||
-              !doesInTreeUserNeedToExtract(Scalar, UserInst, TLI)) {
+              !doesInTreeUserNeedToExtract(
+                  Scalar, cast<Instruction>(UseEntry->Scalars.front()), TLI)) {
             LLVM_DEBUG(dbgs() << "SLP: \tInternal user will be removed:" << *U
                               << ".\n");
             assert(UseEntry->State != TreeEntry::NeedToGather && "Bad state");
             continue;
           }
+          U = nullptr;
         }

+        if (isDeleted(UserInst))
+          continue;
+
         // Ignore users in the user ignore list.
         if (UserIgnoreList && UserIgnoreList->contains(UserInst))
           continue;

         LLVM_DEBUG(dbgs() << "SLP: Need to extract:" << *U << " from lane "
                           << Lane << " from " << *Scalar << ".\n");
-        ExternalUses.push_back(ExternalUser(Scalar, U, FoundLane));
+        ExternalUses.emplace_back(Scalar, U, FoundLane);
       }
     }
   }

``` 

https://github.com/llvm/llvm-project/pull/76077