Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -197,12 +197,51 @@
   return nullptr;
 }
 
+static Value *SimplifyX86insertps(const IntrinsicInst &II,
+                                  InstCombiner::BuilderTy &Builder) {
+  if (auto *CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
+    VectorType *VecTy = cast<VectorType>(II.getType());
+    ConstantAggregateZero *ZeroVector = ConstantAggregateZero::get(VecTy);
+    
+    // The immediate permute control byte looks like this:
+    //    [3:0] - zero mask for each 32-bit lane
+    //    [5:4] - select one 32-bit destination lane
+    //    [7:6] - select one 32-bit source lane
+
+    uint8_t Imm = CInt->getZExtValue();
+    uint8_t ZMask = Imm & 0xf;
+    uint8_t DestLane = (Imm >> 4) & 0x3;
+    uint8_t SourceLane = (Imm >> 6) & 0x3;
+
+    // If all zero mask bits are set, this was just a weird way to
+    // generate a zero vector.
+    if (ZMask == 0xf)
+      return ZeroVector;
+    
+    // TODO: Model this case as two shuffles or a 'logical and' plus shuffle?
+    if (ZMask)
+      return nullptr;
+
+    assert(VecTy->getNumElements() == 4 && "insertps with wrong vector type");
+
+    // If we're not zeroing anything, this is a single shuffle.
+    // Replace the selected destination lane with the selected source lane.
+    // For all other lanes, pass the first source bits through.
+    int ShuffleMask[4] = { 0, 1, 2, 3 };
+    ShuffleMask[DestLane] = SourceLane + 4;
+    
+    return Builder.CreateShuffleVector(II.getArgOperand(0), II.getArgOperand(1),
+                                       ShuffleMask);
+  }
+  return nullptr;
+}
+
 /// The shuffle mask for a perm2*128 selects any two halves of two 256-bit
 /// source vectors, unless a zero bit is set. If a zero bit is set,
 /// then ignore that half of the mask and clear that half of the vector.
 static Value *SimplifyX86vperm2(const IntrinsicInst &II,
                                 InstCombiner::BuilderTy &Builder) {
-  if (auto CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
+  if (auto *CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
     VectorType *VecTy = cast<VectorType>(II.getType());
     ConstantAggregateZero *ZeroVector = ConstantAggregateZero::get(VecTy);
 
@@ -730,7 +769,11 @@
     }
     break;
   }
-
+  case Intrinsic::x86_sse41_insertps:
+    if (Value *V = SimplifyX86insertps(*II, *Builder))
+      return ReplaceInstUsesWith(*II, V);
+    break;
+    
   case Intrinsic::x86_sse4a_insertqi: {
     // insertqi x, y, 64, 0 can just copy y's lower bits and leave the top
     // ones undef
Index: llvm/trunk/test/Transforms/InstCombine/x86-insertps.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/x86-insertps.ll
+++ llvm/trunk/test/Transforms/InstCombine/x86-insertps.ll
@@ -0,0 +1,117 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+declare <4 x float> @llvm.x86.sse41.insertps(<4 x float>, <4 x float>, i8) nounwind readnone
+
+; This should never happen, but make sure we don't crash handling a non-constant immediate byte.
+
+define <4 x float> @insertps_non_const_imm(<4 x float> %v1, <4 x float> %v2, i8 %c) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 %c)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_non_const_imm
+; CHECK-NEXT:  call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 %c)
+; CHECK-NEXT:  ret <4 x float>
+}
+
+; If all zero mask bits are set, return a zero regardless of the other control bits.
+
+define <4 x float> @insertps_0x0f(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 15)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x0f
+; CHECK-NEXT:  ret <4 x float> zeroinitializer
+}
+define <4 x float> @insertps_0xff(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 255)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xff
+; CHECK-NEXT:  ret <4 x float> zeroinitializer
+}
+
+; If some zero mask bits are set, we do not change anything.
+
+define <4 x float> @insertps_0x03(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 3)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x03
+; CHECK-NEXT:  call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 3)
+; CHECK-NEXT:  ret <4 x float>
+}
+
+; If no zero mask bits are set, convert to a shuffle.
+
+define <4 x float> @insertps_0x00(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 0)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x00
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 4, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x10(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 16)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x10
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 4, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x20(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 32)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x20
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 4, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x30(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 48)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x30
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 2, i32 4>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xc0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 192)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xc0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 7, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xd0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 208)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xd0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 7, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xe0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 224)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xe0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 7, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xf0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 240)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xf0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 2, i32 7>
+; CHECK-NEXT:  ret <4 x float>
+}
+