Index: lib/Target/PowerPC/PPCISelDAGToDAG.cpp
===================================================================
--- lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -1331,6 +1331,34 @@
 
       return std::make_pair(Interesting, &Bits);
     }
+    case ISD::TRUNCATE: {
+      EVT FromType = V.getOperand(0).getValueType();
+      EVT ToType = V.getValueType();
+      // We support only the case with truncate from i64 to i32.
+      if (FromType != MVT::i64 || ToType != MVT::i32)
+        break;
+      const unsigned NumAllBits = FromType.getSizeInBits();
+      SmallVector<ValueBit, 64> *InBits;
+      std::tie(Interesting, InBits) = getValueBits(V.getOperand(0),
+                                                    NumAllBits);
+      const unsigned NumValidBits = ToType.getSizeInBits();
+
+      // A 32-bit instruction cannot touch upper 32-bit part of 64-bit value.
+      // So, we cannot include this truncate.
+      bool UseUpper32bit = false;
+      for (unsigned i = 0; i < NumValidBits; ++i)
+        if ((*InBits)[i].hasValue() && (*InBits)[i].getValueBitIndex() >= 32) {
+          UseUpper32bit = true;
+          break;
+        }
+      if (UseUpper32bit)
+        break;
+
+      for (unsigned i = 0; i < NumValidBits; ++i)
+        Bits[i] = (*InBits)[i];
+
+      return std::make_pair(Interesting, &Bits);
+    }
     case ISD::AssertZext: {
       // For AssertZext, we look through the operand and
       // mark the bits known to be zero.
@@ -1676,6 +1704,17 @@
     return ExtVal;
   }
 
+  SDValue TruncateToInt32(SDValue V, const SDLoc &dl) {
+    if (V.getValueSizeInBits() == 32)
+      return V;
+
+    assert(V.getValueSizeInBits() == 64);
+    SDValue SubRegIdx = CurDAG->getTargetConstant(PPC::sub_32, dl, MVT::i32);
+    SDValue SubVal = SDValue(CurDAG->getMachineNode(PPC::EXTRACT_SUBREG, dl,
+                                                    MVT::i32, V, SubRegIdx), 0);
+    return SubVal;
+  }
+
   // Depending on the number of groups for a particular value, it might be
   // better to rotate, mask explicitly (using andi/andis), and then or the
   // result. Select this part of the result first.
@@ -1734,12 +1773,12 @@
       SDValue VRot;
       if (VRI.RLAmt) {
         SDValue Ops[] =
-          { VRI.V, getI32Imm(VRI.RLAmt, dl), getI32Imm(0, dl),
-            getI32Imm(31, dl) };
+          { TruncateToInt32(VRI.V, dl), getI32Imm(VRI.RLAmt, dl),
+            getI32Imm(0, dl), getI32Imm(31, dl) };
         VRot = SDValue(CurDAG->getMachineNode(PPC::RLWINM, dl, MVT::i32,
                                               Ops), 0);
       } else {
-        VRot = VRI.V;
+        VRot = TruncateToInt32(VRI.V, dl);
       }
 
       SDValue ANDIVal, ANDISVal;
@@ -1791,12 +1830,12 @@
       if (VRI.RLAmt) {
         if (InstCnt) *InstCnt += 1;
         SDValue Ops[] =
-          { VRI.V, getI32Imm(VRI.RLAmt, dl), getI32Imm(0, dl),
-            getI32Imm(31, dl) };
+          { TruncateToInt32(VRI.V, dl), getI32Imm(VRI.RLAmt, dl),
+            getI32Imm(0, dl), getI32Imm(31, dl) };
         Res = SDValue(CurDAG->getMachineNode(PPC::RLWINM, dl, MVT::i32, Ops),
                       0);
       } else {
-        Res = VRI.V;
+        Res = TruncateToInt32(VRI.V, dl);
       }
 
       // Now, remove all groups with this underlying value and rotation factor.
@@ -1811,13 +1850,13 @@
     for (auto &BG : BitGroups) {
       if (!Res) {
         SDValue Ops[] =
-          { BG.V, getI32Imm(BG.RLAmt, dl),
+          { TruncateToInt32(BG.V, dl), getI32Imm(BG.RLAmt, dl),
             getI32Imm(Bits.size() - BG.EndIdx - 1, dl),
             getI32Imm(Bits.size() - BG.StartIdx - 1, dl) };
         Res = SDValue(CurDAG->getMachineNode(PPC::RLWINM, dl, MVT::i32, Ops), 0);
       } else {
         SDValue Ops[] =
-          { Res, BG.V, getI32Imm(BG.RLAmt, dl),
+          { Res, TruncateToInt32(BG.V, dl), getI32Imm(BG.RLAmt, dl),
               getI32Imm(Bits.size() - BG.EndIdx - 1, dl),
             getI32Imm(Bits.size() - BG.StartIdx - 1, dl) };
         Res = SDValue(CurDAG->getMachineNode(PPC::RLWIMI, dl, MVT::i32, Ops), 0);
Index: test/CodeGen/PowerPC/bitfieldinsert.ll
===================================================================
--- test/CodeGen/PowerPC/bitfieldinsert.ll
+++ test/CodeGen/PowerPC/bitfieldinsert.ll
@@ -60,3 +60,61 @@
   ret void
 }
 
+; test cases which include ISD::TRUNCATE
+; equivalent C code
+;   struct s64b {
+;     int a:4;
+;     int b:16;
+;     int c:24;
+;   };
+;   void bitfieldinsert64b(struct s64b *p, unsigned char v) {
+;     p->b = v;
+;   }
+
+%struct.s64b = type { i24, i24 }
+
+define void @bitfieldinsert64b(%struct.s64b* nocapture %p, i8 zeroext %v) {
+; CHECK-LABEL: @bitfieldinsert64b
+; CHECK: lwz [[REG1:[0-9]+]], 0(3)
+; CHECK-NEXT: rlwimi [[REG1]], 4, 4, 12, 27
+; CHECK-NEXT: stw [[REG1]], 0(3)
+; CHECK-NEXT: blr
+entry:
+  %conv = zext i8 %v to i32
+  %0 = bitcast %struct.s64b* %p to i32*
+  %bf.load = load i32, i32* %0, align 4
+  %bf.shl = shl nuw nsw i32 %conv, 4
+  %bf.clear = and i32 %bf.load, -1048561
+  %bf.set = or i32 %bf.clear, %bf.shl
+  store i32 %bf.set, i32* %0, align 4
+  ret void
+}
+
+; equivalent C code
+;   struct s64c {
+;     int a:5;
+;     int b:16;
+;     long c:10;
+;   };
+;   void bitfieldinsert64c(struct s64c *p, unsigned short v) {
+;     p->b = v;
+;   }
+
+%struct.s64c = type { i32, [4 x i8] }
+
+define void @bitfieldinsert64c(%struct.s64c* nocapture %p, i16 zeroext %v) {
+; CHECK-LABEL: @bitfieldinsert64c
+; CHECK: lwz [[REG1:[0-9]+]], 0(3)
+; CHECK-NEXT: rlwimi [[REG1]], 4, 5, 11, 26
+; CHECK-NEXT: stw [[REG1]], 0(3)
+; CHECK-NEXT: blr
+entry:
+  %conv = zext i16 %v to i32
+  %0 = getelementptr inbounds %struct.s64c, %struct.s64c* %p, i64 0, i32 0
+  %bf.load = load i32, i32* %0, align 8
+  %bf.shl = shl nuw nsw i32 %conv, 5
+  %bf.clear = and i32 %bf.load, -2097121
+  %bf.set = or i32 %bf.clear, %bf.shl
+  store i32 %bf.set, i32* %0, align 8
+  ret void
+}