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

[via llvm-commits]

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@@ -4925,36 +4925,38 @@ void BoUpSLP::buildExternalUses(
         LLVM_DEBUG(dbgs() << "SLP: Checking user:" << *U << ".\n");
 
         Instruction *UserInst = dyn_cast<Instruction>(U);
-        if (!UserInst)
+        if (!UserInst || isDeleted(UserInst))
           continue;
 
-        if (isDeleted(UserInst))
+        // Ignore users in the user ignore list.
+        if (UserIgnoreList && UserIgnoreList->contains(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;
         }
 
-        // 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));
+        LLVM_DEBUG(dbgs() << "SLP: Need to extract:" << *UserInst
+                          << " from lane " << Lane << " from " << *Scalar
+                          << ".\n");
+        ExternalUses.emplace_back(Scalar, U, FoundLane);
+        // If U == nullptr, all uses of this Scalar will be automatically
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Enna1 wrote:

Sorry, this is not right.
Should not break this `for (User *U : Scalar->users())`, this may exclude some extracts from the cost estimation model.

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