1 files changed, 60 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 96f09084482..0ee6045aeed 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -913,6 +913,61 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
   return nullptr;
 }
 
+/// \brief Look for extractelement/insertvalue sequence that acts like a bitcast.
+///
+/// \returns underlying value that was "cast", or nullptr otherwise.
+///
+/// For example, if we have:
+///
+///     %E0 = extractelement <2 x double> %U, i32 0
+///     %V0 = insertvalue [2 x double] undef, double %E0, 0
+///     %E1 = extractelement <2 x double> %U, i32 1
+///     %V1 = insertvalue [2 x double] %V0, double %E1, 1
+///
+/// and the layout of a <2 x double> is isomorphic to a [2 x double],
+/// then %V1 can be safely approximated by a conceptual "bitcast" of %U.
+/// Note that %U may contain non-undef values where %V1 has undef.
+static Value *likeBitCastFromVector(InstCombiner &IC, Value *V) {
+  Value *U = nullptr;
+  while (auto *IV = dyn_cast<InsertValueInst>(V)) {
+    auto *E = dyn_cast<ExtractElementInst>(IV->getInsertedValueOperand());
+    if (!E)
+      return nullptr;
+    auto *W = E->getVectorOperand();
+    if (!U)
+      U = W;
+    else if (U != W)
+      return nullptr;
+    auto *CI = dyn_cast<ConstantInt>(E->getIndexOperand());
+    if (!CI || IV->getNumIndices() != 1 || CI->getZExtValue() != *IV->idx_begin())
+      return nullptr;
+    V = IV->getAggregateOperand();
+  }
+  if (!isa<UndefValue>(V) ||!U)
+    return nullptr;
+
+  auto *UT = cast<VectorType>(U->getType());
+  auto *VT = V->getType();
+  // Check that types UT and VT are bitwise isomorphic.
+  const auto &DL = IC.getDataLayout();
+  if (DL.getTypeStoreSizeInBits(UT) != DL.getTypeStoreSizeInBits(VT)) {
+    return nullptr;
+  }
+  if (auto *AT = dyn_cast<ArrayType>(VT)) {
+    if (AT->getNumElements() != UT->getNumElements())
+      return nullptr;
+  } else {
+    auto *ST = cast<StructType>(VT);
+    if (ST->getNumElements() != UT->getNumElements())
+      return nullptr;
+    for (const auto *EltT : ST->elements()) {
+      if (EltT != UT->getElementType())
+        return nullptr;
+    }
+  }
+  return U;
+}
+
 /// \brief Combine stores to match the type of value being stored.
 ///
 /// The core idea here is that the memory does not have any intrinsic type and
@@ -948,6 +1003,11 @@ static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
     return true;
   }
 
+  if (Value *U = likeBitCastFromVector(IC, V)) {
+    combineStoreToNewValue(IC, SI, U);
+    return true;
+  }
+
   // FIXME: We should also canonicalize stores of vectors when their elements
   // are cast to other types.
   return false;