[SLP]Do not gather node, if the instruction, that does not require

scheduling, is previously vectorized.

If the main node was vectorized already, but does not require
scheduling, we still can try to vectorize it in this new node instead of
gathering.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -1326,6 +1326,9 @@ class BoUpSLP {
     }
     LLVM_DUMP_METHOD void dump() const { dump(dbgs()); }
 #endif
+    bool operator == (const EdgeInfo &Other) const {
+      return UserTE == Other.UserTE && EdgeIdx == Other.EdgeIdx;
+    }
   };
 
   /// A helper class used for scoring candidates for two consecutive lanes.
@@ -2412,12 +2415,25 @@ class BoUpSLP {
   TreeEntry *getVectorizedOperand(TreeEntry *UserTE, unsigned OpIdx) {
     ArrayRef<Value *> VL = UserTE->getOperand(OpIdx);
     TreeEntry *TE = nullptr;
-    const auto *It = find_if(VL, [this, &TE](Value *V) {
+    const auto *It = find_if(VL, [&](Value *V) {
       TE = getTreeEntry(V);
-      return TE;
+      if (TE && is_contained(TE->UserTreeIndices, EdgeInfo(UserTE, OpIdx)))
+        return true;
+      auto It = MultiNodeScalars.find(V);
+      if (It != MultiNodeScalars.end()) {
+        for (TreeEntry *E : It->second) {
+          if (is_contained(E->UserTreeIndices, EdgeInfo(UserTE, OpIdx))) {
+            TE = E;
+            return true;
+          }
+        }
+      }
+      return false;
     });
-    if (It != VL.end() && TE->isSame(VL))
+    if (It != VL.end()) {
+      assert(TE->isSame(VL) && "Expedted same scalars.");
       return TE;
+    }
     return nullptr;
   }
 
@@ -5806,18 +5822,21 @@ void BoUpSLP::buildTree_rec(ArrayRef<Value *> VL, unsigned Depth,
   if (TreeEntry *E = getTreeEntry(S.OpValue)) {
     LLVM_DEBUG(dbgs() << "SLP: \tChecking bundle: " << *S.OpValue << ".\n");
     if (!E->isSame(VL)) {
-      LLVM_DEBUG(dbgs() << "SLP: Gathering due to partial overlap.\n");
-      if (TryToFindDuplicates(S))
-        newTreeEntry(VL, std::nullopt /*not vectorized*/, S, UserTreeIdx,
-                     ReuseShuffleIndicies);
+      if (!doesNotNeedToBeScheduled(S.OpValue)) {
+        LLVM_DEBUG(dbgs() << "SLP: Gathering due to partial overlap.\n");
+        if (TryToFindDuplicates(S))
+          newTreeEntry(VL, std::nullopt /*not vectorized*/, S, UserTreeIdx,
+                       ReuseShuffleIndicies);
+        return;
+      }
+    } else {
+      // Record the reuse of the tree node.  FIXME, currently this is only used
+      // to properly draw the graph rather than for the actual vectorization.
+      E->UserTreeIndices.push_back(UserTreeIdx);
+      LLVM_DEBUG(dbgs() << "SLP: Perfect diamond merge at " << *S.OpValue
+                        << ".\n");
       return;
     }
-    // Record the reuse of the tree node.  FIXME, currently this is only used to
-    // properly draw the graph rather than for the actual vectorization.
-    E->UserTreeIndices.push_back(UserTreeIdx);
-    LLVM_DEBUG(dbgs() << "SLP: Perfect diamond merge at " << *S.OpValue
-                      << ".\n");
-    return;
   }
 
   // Check that none of the instructions in the bundle are already in the tree.

llvm/test/Transforms/SLPVectorizer/X86/multi-node-vectorized-insts.ll

@@ -83,13 +83,12 @@ define void @test2(double %0) {
 ; CHECK-NEXT:    [[TMP3:%.*]] = shufflevector <2 x double> [[TMP2]], <2 x double> poison, <2 x i32> zeroinitializer
 ; CHECK-NEXT:    br label [[TMP4:%.*]]
 ; CHECK:       4:
-; CHECK-NEXT:    [[TMP5:%.*]] = fsub double 1.000000e+00, [[TMP0]]
-; CHECK-NEXT:    [[TMP6:%.*]] = fsub <2 x double> <double 3.000000e+00, double 2.000000e+00>, [[TMP3]]
+; CHECK-NEXT:    [[TMP5:%.*]] = fsub <2 x double> <double 3.000000e+00, double 2.000000e+00>, [[TMP3]]
+; CHECK-NEXT:    [[TMP6:%.*]] = fsub <2 x double> <double 3.000000e+00, double 1.000000e+00>, [[TMP3]]
 ; CHECK-NEXT:    br label [[DOTBACKEDGE:%.*]]
 ; CHECK:       .backedge:
-; CHECK-NEXT:    [[TMP7:%.*]] = insertelement <2 x double> [[TMP6]], double [[TMP5]], i32 1
-; CHECK-NEXT:    [[TMP8:%.*]] = fmul <2 x double> [[TMP6]], [[TMP7]]
-; CHECK-NEXT:    [[TMP9:%.*]] = fcmp olt <2 x double> [[TMP8]], zeroinitializer
+; CHECK-NEXT:    [[TMP7:%.*]] = fmul <2 x double> [[TMP5]], [[TMP6]]
+; CHECK-NEXT:    [[TMP8:%.*]] = fcmp olt <2 x double> [[TMP7]], zeroinitializer
 ; CHECK-NEXT:    br label [[TMP4]]
 ;
   br label %2