Index: lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -532,14 +532,32 @@
     }
   }
 
-  // Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the dest
-  // type isn't non-native.
   if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
-      ShouldChangeType(SrcTy, DestTy) &&
-      match(Src, m_And(m_Value(A), m_ConstantInt(Cst)))) {
-    Value *NewTrunc = Builder->CreateTrunc(A, DestTy, A->getName() + ".tr");
-    return BinaryOperator::CreateAnd(NewTrunc,
-                                     ConstantExpr::getTrunc(Cst, DestTy));
+      ShouldChangeType(SrcTy, DestTy)) {
+
+    // Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the
+    // dest type is native.
+    if (match(Src, m_And(m_Value(A), m_ConstantInt(Cst)))) {
+      Value *NewTrunc = Builder->CreateTrunc(A, DestTy, A->getName() + ".tr");
+      return BinaryOperator::CreateAnd(NewTrunc,
+                                       ConstantExpr::getTrunc(Cst, DestTy));
+    }
+
+    // Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the
+    // dest type is native and cst < dest size.
+    if (match(Src, m_Shl(m_Value(A), m_ConstantInt(Cst))) &&
+        !match(A, m_Shr(m_Value(), m_Constant()))) {
+      // Skip shifts of shift by constants. It undoes a combine in
+      // FoldShiftByConstant and is the extend in reg pattern.
+      const unsigned DestSize = DestTy->getScalarSizeInBits();
+      if (Cst->getValue().ult(DestSize)) {
+        Value *NewTrunc = Builder->CreateTrunc(A, DestTy, A->getName() + ".tr");
+
+        return BinaryOperator::Create(
+          Instruction::Shl, NewTrunc,
+          ConstantInt::get(DestTy, Cst->getValue().trunc(DestSize)));
+      }
+    }
   }
 
   if (Instruction *I = foldVecTruncToExtElt(CI, *this, DL))
Index: test/Transforms/InstCombine/2011-05-28-swapmulsub.ll
===================================================================
--- test/Transforms/InstCombine/2011-05-28-swapmulsub.ll
+++ test/Transforms/InstCombine/2011-05-28-swapmulsub.ll
@@ -32,7 +32,9 @@
 ; CHECK-NOT: mul i32
   %mul = mul i32 %sub, -4
 ; CHECK: sub i32
-; CHECK-NEXT: shl
+; CHECK-NEXT: trunc i32
+; CHECK-NEXT: %conv = shl i16 %{{.*}}, 2
+; CHECK-NEXT: ret i16 %conv
   store i32 %mul, i32* %a, align 4
   %tmp2 = load i32, i32* %a, align 4
   %conv = trunc i32 %tmp2 to i16
Index: test/Transforms/InstCombine/icmp.ll
===================================================================
--- test/Transforms/InstCombine/icmp.ll
+++ test/Transforms/InstCombine/icmp.ll
@@ -889,9 +889,9 @@
 
 define i1 @test60_addrspacecast_larger(i8 addrspace(1)* %foo, i32 %i, i16 %j) {
 ; CHECK-LABEL: @test60_addrspacecast_larger(
-; CHECK-NEXT:    [[GEP1_IDX:%.*]] = shl nuw i32 %i, 2
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[GEP1_IDX]] to i16
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i16 [[TMP1]], %j
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 %i to i16
+; CHECK-NEXT:    [[SHL:%.*]] = shl i16 [[TMP1]], 2
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i16 [[SHL]], %j
 ; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %bit = addrspacecast i8 addrspace(1)* %foo to i32 addrspace(2)*
Index: test/Transforms/InstCombine/trunc.ll
===================================================================
--- test/Transforms/InstCombine/trunc.ll
+++ test/Transforms/InstCombine/trunc.ll
@@ -160,24 +160,245 @@
 ; CHECK-NEXT:  ret i32 %ext
 }
 
-; CHECK-LABEL: @trunc_shl_infloop(
-; CHECK: %tmp = lshr i64 %arg, 1
-; CHECK: %tmp21 = shl i64 %tmp, 2
-; CHECK: %tmp2 = trunc i64 %tmp21 to i32
-; CHECK: icmp sgt i32 %tmp2, 0
-define void @trunc_shl_infloop(i64 %arg) {
-bb:
-  %tmp = lshr i64 %arg, 1
-  %tmp1 = trunc i64 %tmp to i32
-  %tmp2 = shl i32 %tmp1, 2
-  %tmp3 = icmp sgt i32 %tmp2, 0
-  br i1 %tmp3, label %bb2, label %bb1
-
-bb1:
-  %tmp5 = sub i32 0, %tmp1
-  %tmp6 = sub i32 %tmp5, 1
-  unreachable
-
-bb2:
-  unreachable
+; CHECK-LABEL: @trunc_shl_31_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 31
+define i32 @trunc_shl_31_i32_i64(i64 %val) {
+  %shl = shl i64 %val, 31
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_nsw_31_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 31
+define i32 @trunc_shl_nsw_31_i32_i64(i64 %val) {
+  %shl = shl nsw i64 %val, 31
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_nuw_31_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 31
+define i32 @trunc_shl_nuw_31_i32_i64(i64 %val) {
+  %shl = shl nuw i64 %val, 31
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_nsw_nuw_31_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 31
+define i32 @trunc_shl_nsw_nuw_31_i32_i64(i64 %val) {
+  %shl = shl nsw nuw i64 %val, 31
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_15_i16_i64(
+; CHECK: %val.tr = trunc i64 %val to i16
+; CHECK-NEXT: shl i16 %val.tr, 15
+define i16 @trunc_shl_15_i16_i64(i64 %val) {
+  %shl = shl i64 %val, 15
+  %trunc = trunc i64 %shl to i16
+  ret i16 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_15_i16_i32(
+; CHECK: %val.tr = trunc i32 %val to i16
+; CHECK-NEXT: shl i16 %val.tr, 15
+define i16 @trunc_shl_15_i16_i32(i32 %val) {
+  %shl = shl i32 %val, 15
+  %trunc = trunc i32 %shl to i16
+  ret i16 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_7_i8_i64(
+; CHECK: %val.tr = trunc i64 %val to i8
+; CHECK-NEXT: shl i8 %val.tr, 7
+define i8 @trunc_shl_7_i8_i64(i64 %val) {
+  %shl = shl i64 %val, 7
+  %trunc = trunc i64 %shl to i8
+  ret i8 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_1_i2_i64(
+; CHECK: shl i64 %val, 1
+; CHECK-NEXT: trunc i64 %shl to i2
+define i2 @trunc_shl_1_i2_i64(i64 %val) {
+  %shl = shl i64 %val, 1
+  %trunc = trunc i64 %shl to i2
+  ret i2 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_1_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 1
+define i32 @trunc_shl_1_i32_i64(i64 %val) {
+  %shl = shl i64 %val, 1
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_16_i32_i64(
+; CHECK: %val.tr = trunc i64 %val to i32
+; CHECK-NEXT: shl i32 %val.tr, 16
+define i32 @trunc_shl_16_i32_i64(i64 %val) {
+  %shl = shl i64 %val, 16
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_33_i32_i64(
+; CHECK: ret i32 0
+define i32 @trunc_shl_33_i32_i64(i64 %val) {
+  %shl = shl i64 %val, 33
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_32_i32_i64(
+; CHECK: ret i32 0
+define i32 @trunc_shl_32_i32_i64(i64 %val) {
+  %shl = shl i64 %val, 32
+  %trunc = trunc i64 %shl to i32
+  ret i32 %trunc
+}
+
+; TODO: Should be able to handle vectors
+; CHECK-LABEL: @trunc_shl_16_v2i32_v2i64(
+; CHECK: shl <2 x i64>
+define <2 x i32> @trunc_shl_16_v2i32_v2i64(<2 x i64> %val) {
+  %shl = shl <2 x i64> %val, <i64 16, i64 16>
+  %trunc = trunc <2 x i64> %shl to <2 x i32>
+  ret <2 x i32> %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_nosplat_v2i32_v2i64(
+; CHECK: shl <2 x i64>
+define <2 x i32> @trunc_shl_nosplat_v2i32_v2i64(<2 x i64> %val) {
+  %shl = shl <2 x i64> %val, <i64 15, i64 16>
+  %trunc = trunc <2 x i64> %shl to <2 x i32>
+  ret <2 x i32> %trunc
+}
+
+; CHECK-LABEL: @trunc_shl_31_i32_i64_multi_use(
+; CHECK: shl i64 %val, 31
+; CHECK-NOT: shl i32
+; CHECK: trunc i64 %shl to i32
+; CHECK-NOT: shl i32
+define void @trunc_shl_31_i32_i64_multi_use(i64 %val, i32 addrspace(1)* %ptr0, i64 addrspace(1)* %ptr1) {
+  %shl = shl i64 %val, 31
+  %trunc = trunc i64 %shl to i32
+  store volatile i32 %trunc, i32 addrspace(1)* %ptr0
+  store volatile i64 %shl, i64 addrspace(1)* %ptr1
+  ret void
+}
+
+; CHECK-LABEL: @trunc_shl_lshr_infloop(
+; CHECK-NEXT: %tmp0 = lshr i64 %arg, 1
+; CHECK-NEXT: %tmp1 = shl i64 %tmp0, 2
+; CHECK-NEXT: %tmp2 = trunc i64 %tmp1 to i32
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_lshr_infloop(i64 %arg) {
+  %tmp0 = lshr i64 %arg, 1
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_ashr_infloop(
+; CHECK-NEXT: %tmp0 = ashr i64 %arg, 3
+; CHECK-NEXT: %tmp1 = shl nsw i64 %tmp0, 2
+; CHECK-NEXT: %tmp2 = trunc i64 %tmp1 to i32
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_ashr_infloop(i64 %arg) {
+  %tmp0 = ashr i64 %arg, 3
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_shl_infloop(
+; CHECK-NEXT: %arg.tr = trunc i64 %arg to i32
+; CHECK-NEXT: %tmp2 = shl i32 %arg.tr, 3
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_shl_infloop(i64 %arg) {
+  %tmp0 = shl i64 %arg, 1
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_lshr_var(
+; CHECK-NEXT: %tmp0 = lshr i64 %arg, %val
+; CHECK-NEXT: %tmp0.tr = trunc i64 %tmp0 to i32
+; CHECK-NEXT: %tmp2 = shl i32 %tmp0.tr, 2
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_lshr_var(i64 %arg, i64 %val) {
+  %tmp0 = lshr i64 %arg, %val
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_ashr_var(
+; CHECK-NEXT: %tmp0 = ashr i64 %arg, %val
+; CHECK-NEXT: %tmp0.tr = trunc i64 %tmp0 to i32
+; CHECK-NEXT: %tmp2 = shl i32 %tmp0.tr, 2
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_ashr_var(i64 %arg, i64 %val) {
+  %tmp0 = ashr i64 %arg, %val
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_shl_var(
+; CHECK-NEXT: %tmp0 = shl i64 %arg, %val
+; CHECK-NEXT: %tmp0.tr = trunc i64 %tmp0 to i32
+; CHECK-NEXT: %tmp2 = shl i32 %tmp0.tr, 2
+; CHECK-NEXT: ret i32 %tmp2
+define i32 @trunc_shl_shl_var(i64 %arg, i64 %val) {
+  %tmp0 = shl i64 %arg, %val
+  %tmp1 = shl i64 %tmp0, 2
+  %tmp2 = trunc i64 %tmp1 to i32
+  ret i32 %tmp2
+}
+
+; CHECK-LABEL: @trunc_shl_v8i15_v8i32_15(
+; CHECK: %shl = shl <8 x i32> %a, <i32 15,
+; CHECK: trunc <8 x i32> %shl to <8 x i16>
+define <8 x i16> @trunc_shl_v8i15_v8i32_15(<8 x i32> %a) {
+  %shl = shl <8 x i32> %a, <i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15, i32 15>
+  %conv = trunc <8 x i32> %shl to <8 x i16>
+  ret <8 x i16> %conv
+}
+
+; CHECK-LABEL: @trunc_shl_v8i16_v8i32_16(
+; CHECK: %shl = shl <8 x i32> %a, <i32 16
+; CHECK: trunc <8 x i32> %shl to <8 x i16>
+define <8 x i16> @trunc_shl_v8i16_v8i32_16(<8 x i32> %a) {
+  %shl = shl <8 x i32> %a, <i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16, i32 16>
+  %conv = trunc <8 x i32> %shl to <8 x i16>
+  ret <8 x i16> %conv
+}
+
+; CHECK-LABEL: @trunc_shl_v8i16_v8i32_17(
+; CHECK: %shl = shl <8 x i32> %a, <i32 17
+; CHECK: %conv = trunc <8 x i32> %shl to <8 x i16>
+define <8 x i16> @trunc_shl_v8i16_v8i32_17(<8 x i32> %a) {
+  %shl = shl <8 x i32> %a, <i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17>
+  %conv = trunc <8 x i32> %shl to <8 x i16>
+  ret <8 x i16> %conv
+}
+
+; CHECK-LABEL: @trunc_shl_v8i16_v8i32_4(
+; CHECK: %shl = shl <8 x i32> %a, <i32 4, i32 4, i32 4, i32 4, i32 4, i32 4, i32 4, i32 4>
+; CHECK: trunc <8 x i32> %shl to <8 x i16>
+define <8 x i16> @trunc_shl_v8i16_v8i32_4(<8 x i32> %a) {
+  %shl = shl <8 x i32> %a, <i32 4, i32 4, i32 4, i32 4, i32 4, i32 4, i32 4, i32 4>
+  %conv = trunc <8 x i32> %shl to <8 x i16>
+  ret <8 x i16> %conv
 }