Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -198,8 +198,52 @@
 }
 
 static Value *SimplifyX86immshift(const IntrinsicInst &II,
-                                  InstCombiner::BuilderTy &Builder,
-                                  bool LogicalShift, bool ShiftLeft) {
+                                  InstCombiner::BuilderTy &Builder) {
+  bool LogicalShift = false;
+  bool ShiftLeft = false;
+
+  switch (II.getIntrinsicID()) {
+  default:
+    return nullptr;
+  case Intrinsic::x86_sse2_psra_d:
+  case Intrinsic::x86_sse2_psra_w:
+  case Intrinsic::x86_sse2_psrai_d:
+  case Intrinsic::x86_sse2_psrai_w:
+  case Intrinsic::x86_avx2_psra_d:
+  case Intrinsic::x86_avx2_psra_w:
+  case Intrinsic::x86_avx2_psrai_d:
+  case Intrinsic::x86_avx2_psrai_w:
+    LogicalShift = false; ShiftLeft = false;
+    break;
+  case Intrinsic::x86_sse2_psrl_d:
+  case Intrinsic::x86_sse2_psrl_q:
+  case Intrinsic::x86_sse2_psrl_w:
+  case Intrinsic::x86_sse2_psrli_d:
+  case Intrinsic::x86_sse2_psrli_q:
+  case Intrinsic::x86_sse2_psrli_w:
+  case Intrinsic::x86_avx2_psrl_d:
+  case Intrinsic::x86_avx2_psrl_q:
+  case Intrinsic::x86_avx2_psrl_w:
+  case Intrinsic::x86_avx2_psrli_d:
+  case Intrinsic::x86_avx2_psrli_q:
+  case Intrinsic::x86_avx2_psrli_w:
+    LogicalShift = true; ShiftLeft = false;
+    break;
+  case Intrinsic::x86_sse2_psll_d:
+  case Intrinsic::x86_sse2_psll_q:
+  case Intrinsic::x86_sse2_psll_w:
+  case Intrinsic::x86_sse2_pslli_d:
+  case Intrinsic::x86_sse2_pslli_q:
+  case Intrinsic::x86_sse2_pslli_w:
+  case Intrinsic::x86_avx2_psll_d:
+  case Intrinsic::x86_avx2_psll_q:
+  case Intrinsic::x86_avx2_psll_w:
+  case Intrinsic::x86_avx2_pslli_d:
+  case Intrinsic::x86_avx2_pslli_q:
+  case Intrinsic::x86_avx2_pslli_w:
+    LogicalShift = true; ShiftLeft = true;
+    break;
+  }
   assert((LogicalShift || !ShiftLeft) && "Only logical shifts can shift left");
 
   // Simplify if count is constant.
@@ -788,51 +832,64 @@
   }
 
   // Constant fold ashr( <A x Bi>, Ci ).
-  case Intrinsic::x86_sse2_psra_d:
-  case Intrinsic::x86_sse2_psra_w:
+  // Constant fold lshr( <A x Bi>, Ci ).
+  // Constant fold shl( <A x Bi>, Ci ).
   case Intrinsic::x86_sse2_psrai_d:
   case Intrinsic::x86_sse2_psrai_w:
-  case Intrinsic::x86_avx2_psra_d:
-  case Intrinsic::x86_avx2_psra_w:
   case Intrinsic::x86_avx2_psrai_d:
   case Intrinsic::x86_avx2_psrai_w:
-    if (Value *V = SimplifyX86immshift(*II, *Builder, false, false))
-      return ReplaceInstUsesWith(*II, V);
-    break;
-
-  // Constant fold lshr( <A x Bi>, Ci ).
-  case Intrinsic::x86_sse2_psrl_d:
-  case Intrinsic::x86_sse2_psrl_q:
-  case Intrinsic::x86_sse2_psrl_w:
   case Intrinsic::x86_sse2_psrli_d:
   case Intrinsic::x86_sse2_psrli_q:
   case Intrinsic::x86_sse2_psrli_w:
-  case Intrinsic::x86_avx2_psrl_d:
-  case Intrinsic::x86_avx2_psrl_q:
-  case Intrinsic::x86_avx2_psrl_w:
   case Intrinsic::x86_avx2_psrli_d:
   case Intrinsic::x86_avx2_psrli_q:
   case Intrinsic::x86_avx2_psrli_w:
-    if (Value *V = SimplifyX86immshift(*II, *Builder, true, false))
+  case Intrinsic::x86_sse2_pslli_d:
+  case Intrinsic::x86_sse2_pslli_q:
+  case Intrinsic::x86_sse2_pslli_w:
+  case Intrinsic::x86_avx2_pslli_d:
+  case Intrinsic::x86_avx2_pslli_q:
+  case Intrinsic::x86_avx2_pslli_w:
+    if (Value *V = SimplifyX86immshift(*II, *Builder))
       return ReplaceInstUsesWith(*II, V);
     break;
 
-  // Constant fold shl( <A x Bi>, Ci ).
+  case Intrinsic::x86_sse2_psra_d:
+  case Intrinsic::x86_sse2_psra_w:
+  case Intrinsic::x86_avx2_psra_d:
+  case Intrinsic::x86_avx2_psra_w:
+  case Intrinsic::x86_sse2_psrl_d:
+  case Intrinsic::x86_sse2_psrl_q:
+  case Intrinsic::x86_sse2_psrl_w:
+  case Intrinsic::x86_avx2_psrl_d:
+  case Intrinsic::x86_avx2_psrl_q:
+  case Intrinsic::x86_avx2_psrl_w:
   case Intrinsic::x86_sse2_psll_d:
   case Intrinsic::x86_sse2_psll_q:
   case Intrinsic::x86_sse2_psll_w:
-  case Intrinsic::x86_sse2_pslli_d:
-  case Intrinsic::x86_sse2_pslli_q:
-  case Intrinsic::x86_sse2_pslli_w:
   case Intrinsic::x86_avx2_psll_d:
   case Intrinsic::x86_avx2_psll_q:
-  case Intrinsic::x86_avx2_psll_w:
-  case Intrinsic::x86_avx2_pslli_d:
-  case Intrinsic::x86_avx2_pslli_q:
-  case Intrinsic::x86_avx2_pslli_w:
-    if (Value *V = SimplifyX86immshift(*II, *Builder, true, true))
+  case Intrinsic::x86_avx2_psll_w: {
+    if (Value *V = SimplifyX86immshift(*II, *Builder))
       return ReplaceInstUsesWith(*II, V);
+
+    // SSE2/AVX2 only uses all the first 64-bits of the 128-bit vector
+    // operand to compute the shift amount.
+    auto ShiftAmt = II->getArgOperand(1);
+    auto ShiftType = cast<VectorType>(ShiftAmt->getType());
+    assert(ShiftType->getPrimitiveSizeInBits() == 128 &&
+           "Unexpected packed shift size");
+    unsigned VWidth = ShiftType->getNumElements();
+
+    APInt DemandedElts = APInt::getLowBitsSet(VWidth, VWidth / 2);
+    APInt UndefElts(VWidth, 0);
+    if (Value *V =
+            SimplifyDemandedVectorElts(ShiftAmt, DemandedElts, UndefElts)) {
+      II->setArgOperand(1, V);
+      return II;
+    }
     break;
+  }
 
   case Intrinsic::x86_sse41_pmovsxbd:
   case Intrinsic::x86_sse41_pmovsxbq:
Index: test/Transforms/InstCombine/x86-vector-shifts.ll
===================================================================
--- test/Transforms/InstCombine/x86-vector-shifts.ll
+++ test/Transforms/InstCombine/x86-vector-shifts.ll
@@ -826,6 +826,154 @@
 }
 
 ;
+; Vector Demanded Bits
+;
+
+define <8 x i16> @sse2_psra_w_var(<8 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psra_w_var
+; CHECK-NEXT: %1 = tail call <8 x i16> @llvm.x86.sse2.psra.w(<8 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <8 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <8 x i16> @llvm.x86.sse2.psra.w(<8 x i16> %v, <8 x i16> %1)
+  ret <8 x i16> %2
+}
+
+define <4 x i32> @sse2_psra_d_var(<4 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psra_d_var
+; CHECK-NEXT: %1 = tail call <4 x i32> @llvm.x86.sse2.psra.d(<4 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <4 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <4 x i32> @llvm.x86.sse2.psra.d(<4 x i32> %v, <4 x i32> %1)
+  ret <4 x i32> %2
+}
+
+define <16 x i16> @avx2_psra_w_var(<16 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psra_w_var
+; CHECK-NEXT: %1 = tail call <16 x i16> @llvm.x86.avx2.psra.w(<16 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <16 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <16 x i16> @llvm.x86.avx2.psra.w(<16 x i16> %v, <8 x i16> %1)
+  ret <16 x i16> %2
+}
+
+define <8 x i32> @avx2_psra_d_var(<8 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psra_d_var
+; CHECK-NEXT: %1 = tail call <8 x i32> @llvm.x86.avx2.psra.d(<8 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <8 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <8 x i32> @llvm.x86.avx2.psra.d(<8 x i32> %v, <4 x i32> %1)
+  ret <8 x i32> %2
+}
+
+define <8 x i16> @sse2_psrl_w_var(<8 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psrl_w_var
+; CHECK-NEXT: %1 = tail call <8 x i16> @llvm.x86.sse2.psrl.w(<8 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <8 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <8 x i16> @llvm.x86.sse2.psrl.w(<8 x i16> %v, <8 x i16> %1)
+  ret <8 x i16> %2
+}
+
+define <4 x i32> @sse2_psrl_d_var(<4 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psrl_d_var
+; CHECK-NEXT: %1 = tail call <4 x i32> @llvm.x86.sse2.psrl.d(<4 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <4 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <4 x i32> @llvm.x86.sse2.psrl.d(<4 x i32> %v, <4 x i32> %1)
+  ret <4 x i32> %2
+}
+
+define <2 x i64> @sse2_psrl_q_var(<2 x i64> %v, <2 x i64> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psrl_q_var
+; CHECK-NEXT: %1 = tail call <2 x i64> @llvm.x86.sse2.psrl.q(<2 x i64> %v, <2 x i64> %a)
+; CHECK-NEXT: ret <2 x i64> %1
+  %1 = shufflevector <2 x i64> %a, <2 x i64> undef, <2 x i32> <i32 0, i32 0>
+  %2 = tail call <2 x i64> @llvm.x86.sse2.psrl.q(<2 x i64> %v, <2 x i64> %1)
+  ret <2 x i64> %2
+}
+
+define <16 x i16> @avx2_psrl_w_var(<16 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psrl_w_var
+; CHECK-NEXT: %1 = tail call <16 x i16> @llvm.x86.avx2.psrl.w(<16 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <16 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <16 x i16> @llvm.x86.avx2.psrl.w(<16 x i16> %v, <8 x i16> %1)
+  ret <16 x i16> %2
+}
+
+define <8 x i32> @avx2_psrl_d_var(<8 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psrl_d_var
+; CHECK-NEXT: %1 = tail call <8 x i32> @llvm.x86.avx2.psrl.d(<8 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <8 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <8 x i32> @llvm.x86.avx2.psrl.d(<8 x i32> %v, <4 x i32> %1)
+  ret <8 x i32> %2
+}
+
+define <4 x i64> @avx2_psrl_q_var(<4 x i64> %v, <2 x i64> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psrl_q_var
+; CHECK-NEXT: %1 = tail call <4 x i64> @llvm.x86.avx2.psrl.q(<4 x i64> %v, <2 x i64> %a)
+; CHECK-NEXT: ret <4 x i64> %1
+  %1 = shufflevector <2 x i64> %a, <2 x i64> undef, <2 x i32> <i32 0, i32 0>
+  %2 = tail call <4 x i64> @llvm.x86.avx2.psrl.q(<4 x i64> %v, <2 x i64> %1)
+  ret <4 x i64> %2
+}
+
+define <8 x i16> @sse2_psll_w_var(<8 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psll_w_var
+; CHECK-NEXT: %1 = tail call <8 x i16> @llvm.x86.sse2.psll.w(<8 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <8 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <8 x i16> @llvm.x86.sse2.psll.w(<8 x i16> %v, <8 x i16> %1)
+  ret <8 x i16> %2
+}
+
+define <4 x i32> @sse2_psll_d_var(<4 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psll_d_var
+; CHECK-NEXT: %1 = tail call <4 x i32> @llvm.x86.sse2.psll.d(<4 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <4 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <4 x i32> @llvm.x86.sse2.psll.d(<4 x i32> %v, <4 x i32> %1)
+  ret <4 x i32> %2
+}
+
+define <2 x i64> @sse2_psll_q_var(<2 x i64> %v, <2 x i64> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @sse2_psll_q_var
+; CHECK-NEXT: %1 = tail call <2 x i64> @llvm.x86.sse2.psll.q(<2 x i64> %v, <2 x i64> %a)
+; CHECK-NEXT: ret <2 x i64> %1
+  %1 = shufflevector <2 x i64> %a, <2 x i64> undef, <2 x i32> <i32 0, i32 0>
+  %2 = tail call <2 x i64> @llvm.x86.sse2.psll.q(<2 x i64> %v, <2 x i64> %1)
+  ret <2 x i64> %2
+}
+
+define <16 x i16> @avx2_psll_w_var(<16 x i16> %v, <8 x i16> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psll_w_var
+; CHECK-NEXT: %1 = tail call <16 x i16> @llvm.x86.avx2.psll.w(<16 x i16> %v, <8 x i16> %a)
+; CHECK-NEXT: ret <16 x i16> %1
+  %1 = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 0, i32 1, i32 2, i32 3>
+  %2 = tail call <16 x i16> @llvm.x86.avx2.psll.w(<16 x i16> %v, <8 x i16> %1)
+  ret <16 x i16> %2
+}
+
+define <8 x i32> @avx2_psll_d_var(<8 x i32> %v, <4 x i32> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psll_d_var
+; CHECK-NEXT: %1 = tail call <8 x i32> @llvm.x86.avx2.psll.d(<8 x i32> %v, <4 x i32> %a)
+; CHECK-NEXT: ret <8 x i32> %1
+  %1 = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 0, i32 1>
+  %2 = tail call <8 x i32> @llvm.x86.avx2.psll.d(<8 x i32> %v, <4 x i32> %1)
+  ret <8 x i32> %2
+}
+
+define <4 x i64> @avx2_psll_q_var(<4 x i64> %v, <2 x i64> %a) nounwind readnone uwtable {
+; CHECK-LABEL: @avx2_psll_q_var
+; CHECK-NEXT: %1 = tail call <4 x i64> @llvm.x86.avx2.psll.q(<4 x i64> %v, <2 x i64> %a)
+; CHECK-NEXT: ret <4 x i64> %1
+  %1 = shufflevector <2 x i64> %a, <2 x i64> undef, <2 x i32> <i32 0, i32 0>
+  %2 = tail call <4 x i64> @llvm.x86.avx2.psll.q(<4 x i64> %v, <2 x i64> %1)
+  ret <4 x i64> %2
+}
+
+;
 ; Constant Folding
 ;