1 files changed, 14 insertions, 4 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 99d3d478aaf..99874b31912 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1393,7 +1393,10 @@ Instruction *InstCombiner::foldShuffledBinop(BinaryOperator &Inst) {
   if (match(&Inst, m_c_BinOp(
           m_OneUse(m_ShuffleVector(m_Value(V1), m_Undef(), m_Constant(Mask))),
           m_Constant(C))) &&
-      V1->getType() == Inst.getType()) {
+      V1->getType()->getVectorNumElements() <= VWidth) {
+    assert(Inst.getType()->getScalarType() == V1->getType()->getScalarType() &&
+           "Shuffle should not change scalar type");
+    unsigned V1Width = V1->getType()->getVectorNumElements();
     // Find constant NewC that has property:
     //   shuffle(NewC, ShMask) = C
     // If such constant does not exist (example: ShMask=<0,0> and C=<1,2>)
@@ -1402,14 +1405,21 @@ Instruction *InstCombiner::foldShuffledBinop(BinaryOperator &Inst) {
     SmallVector<int, 16> ShMask;
     ShuffleVectorInst::getShuffleMask(Mask, ShMask);
     SmallVector<Constant *, 16>
-        NewVecC(VWidth, UndefValue::get(C->getType()->getScalarType()));
+        NewVecC(V1Width, UndefValue::get(C->getType()->getScalarType()));
     bool MayChange = true;
     for (unsigned I = 0; I < VWidth; ++I) {
       if (ShMask[I] >= 0) {
-        assert(ShMask[I] < (int)VWidth);
+        assert(ShMask[I] < (int)VWidth && "Not expecting narrowing shuffle");
         Constant *CElt = C->getAggregateElement(I);
         Constant *NewCElt = NewVecC[ShMask[I]];
-        if (!CElt || (!isa<UndefValue>(NewCElt) && NewCElt != CElt)) {
+        // Bail out if:
+        // 1. The constant vector contains a constant expression.
+        // 2. The shuffle needs an element of the constant vector that can't
+        //    be mapped to a new constant vector.
+        // 3. This is a widening shuffle that copies elements of V1 into the
+        //    extended elements (extending with undef is allowed).
+        if (!CElt || (!isa<UndefValue>(NewCElt) && NewCElt != CElt) ||
+            I >= V1Width) {
           MayChange = false;
           break;
         }