diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -15427,13 +15427,13 @@
           !ST1->getBasePtr().isUndef()) {
         const BaseIndexOffset STBase = BaseIndexOffset::match(ST, DAG);
         const BaseIndexOffset ChainBase = BaseIndexOffset::match(ST1, DAG);
-        unsigned STByteSize = ST->getMemoryVT().getSizeInBits() / 8;
-        unsigned ChainByteSize = ST1->getMemoryVT().getSizeInBits() / 8;
+        unsigned STBitSize = ST->getMemoryVT().getSizeInBits();
+        unsigned ChainBitSize = ST1->getMemoryVT().getSizeInBits();
         // If this is a store who's preceding store to a subset of the current
         // location and no one other node is chained to that store we can
         // effectively drop the store. Do not remove stores to undef as they may
         // be used as data sinks.
-        if (STBase.contains(STByteSize, ChainBase, ChainByteSize, DAG)) {
+        if (STBase.contains((STBitSize+7)/8, ChainBase, (ChainBitSize+7)/8, DAG)) {
           CombineTo(ST1, ST1->getChain());
           return SDValue();
         }
@@ -15443,13 +15443,13 @@
         // the other uses of ST1's chain are unconcerned with ST, this folding
         // will not affect those nodes.
         int64_t Offset;
-        if (ChainBase.contains(ChainByteSize, STBase, STByteSize, DAG,
+        if (ChainBase.contains((ChainBitSize+7)/8, STBase, (STBitSize+7)/8, DAG,
                                Offset)) {
           SDValue ChainValue = ST1->getValue();
           if (auto *C1 = dyn_cast<ConstantSDNode>(ChainValue)) {
             if (auto *C = dyn_cast<ConstantSDNode>(Value)) {
               APInt Val = C1->getAPIntValue();
-              APInt InsertVal = C->getAPIntValue().zextOrTrunc(STByteSize * 8);
+              APInt InsertVal = C->getAPIntValue().zextOrTrunc(STBitSize);
               // FIXME: Handle Big-endian mode.
               if (!DAG.getDataLayout().isBigEndian()) {
                 Val.insertBits(InsertVal, Offset * 8);
diff --git a/llvm/test/CodeGen/X86/constant-combines.ll b/llvm/test/CodeGen/X86/constant-combines.ll
--- a/llvm/test/CodeGen/X86/constant-combines.ll
+++ b/llvm/test/CodeGen/X86/constant-combines.ll
@@ -38,3 +38,15 @@
   store float %8, float* %0, align 4
   ret void
 }
+
+
+define void @bitstore_fold() {
+; CHECK-LABEL: bitstore_fold:
+; CHECK:       # %bb.0: # %BB
+; CHECK-NEXT:    movl $-2, 0
+; CHECK-NEXT:    retq
+BB:
+   store i32 -1, i32* null
+   store i1 false, i1* null
+   ret void
+}