diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -7159,6 +7159,7 @@
   finalize(ArrayRef<int> ExtMask, unsigned VF = 0,
            function_ref<void(Value *&, SmallVectorImpl<int> &)> Action = {}) {
     IsFinalized = true;
+    bool ShouldExtendManyInputs = (InVectors.size() > 1);
     if (Action) {
       const PointerUnion<Value *, const TreeEntry *> &Vec = InVectors.front();
       if (InVectors.size() == 2) {
@@ -7179,7 +7180,7 @@
             CommonMask.size()));
       Action(V, CommonMask);
     }
-    ::addMask(CommonMask, ExtMask, /*ExtendingManyInputs=*/true);
+    ::addMask(CommonMask, ExtMask, /*ExtendingManyInputs=*/ShouldExtendManyInputs);
     if (CommonMask.empty())
       return Cost;
     int Limit = CommonMask.size() * 2;
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/pr63668.ll b/llvm/test/Transforms/SLPVectorizer/X86/pr63668.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/X86/pr63668.ll
@@ -0,0 +1,54 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -passes=slp-vectorizer -mtriple=x86_64-unknown-linux-gnu -mcpu=znver4 -S < %s | FileCheck %s
+
+define internal i32 @testfunc() {
+; CHECK-LABEL: define internal i32 @testfunc
+; CHECK-SAME: () #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    br label [[TMP1:%.*]]
+; CHECK:       1:
+; CHECK-NEXT:    [[TMP2:%.*]] = phi float [ 0.000000e+00, [[TMP0:%.*]] ], [ 0.000000e+00, [[TMP8:%.*]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = phi float [ 0.000000e+00, [[TMP0]] ], [ 0.000000e+00, [[TMP8]] ]
+; CHECK-NEXT:    [[TMP4:%.*]] = phi float [ 0.000000e+00, [[TMP0]] ], [ 0.000000e+00, [[TMP8]] ]
+; CHECK-NEXT:    br i1 false, label [[TMP8]], label [[TMP5:%.*]]
+; CHECK:       5:
+; CHECK-NEXT:    br i1 false, label [[TMP6:%.*]], label [[TMP8]]
+; CHECK:       6:
+; CHECK-NEXT:    [[TMP7:%.*]] = extractelement <8 x float> zeroinitializer, i64 0
+; CHECK-NEXT:    br label [[TMP8]]
+; CHECK:       8:
+; CHECK-NEXT:    [[TMP9:%.*]] = phi float [ [[TMP7]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP10:%.*]] = phi float [ [[TMP2]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ [[TMP2]], [[TMP5]] ]
+; CHECK-NEXT:    [[TMP11:%.*]] = phi float [ [[TMP7]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP12:%.*]] = phi float [ [[TMP7]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP13:%.*]] = phi float [ [[TMP7]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP14:%.*]] = phi float [ [[TMP3]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP15:%.*]] = phi float [ [[TMP4]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ 0.000000e+00, [[TMP5]] ]
+; CHECK-NEXT:    [[TMP16:%.*]] = phi float [ [[TMP4]], [[TMP6]] ], [ 0.000000e+00, [[TMP1]] ], [ [[TMP3]], [[TMP5]] ]
+; CHECK-NEXT:    br label [[TMP1]]
+;
+  br label %1
+
+1:                                                ; preds = %8, %0
+  %2 = phi float [ 0.000000e+00, %0 ], [ 0.000000e+00, %8 ]
+  %3 = phi float [ 0.000000e+00, %0 ], [ 0.000000e+00, %8 ]
+  %4 = phi float [ 0.000000e+00, %0 ], [ 0.000000e+00, %8 ]
+  br i1 false, label %8, label %5
+
+5:                                                ; preds = %1
+  br i1 false, label %6, label %8
+
+6:                                                ; preds = %5
+  %7 = extractelement <8 x float> zeroinitializer, i64 0
+  br label %8
+
+8:                                                ; preds = %6, %5, %1
+  %9 = phi float [ %7, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %10 = phi float [ %2, %6 ], [ 0.000000e+00, %1 ], [ %2, %5 ]
+  %11 = phi float [ %7, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %12 = phi float [ %7, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %13 = phi float [ %7, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %14 = phi float [ %3, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %15 = phi float [ %4, %6 ], [ 0.000000e+00, %1 ], [ 0.000000e+00, %5 ]
+  %16 = phi float [ %4, %6 ], [ 0.000000e+00, %1 ], [ %3, %5 ]
+  br label %1
+}