[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

@@ -5811,18 +5811,21 @@ 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