Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -600,11 +600,11 @@
   if (Instruction *V = commonShiftTransforms(I))
     return V;
 
+  Type *Ty = I.getType();
   const APInt *ShAmtAPInt;
   if (match(Op1, m_APInt(ShAmtAPInt))) {
     unsigned ShAmt = ShAmtAPInt->getZExtValue();
     unsigned BitWidth = I.getType()->getScalarSizeInBits();
-    Type *Ty = I.getType();
 
     // shl (zext X), ShAmt --> zext (shl X, ShAmt)
     // This is only valid if X would have zeros shifted out.
@@ -670,6 +670,15 @@
     }
   }
 
+  // Transform  (x >> y) << y  to  x & (-1 << y)
+  // Valid for any type of right-shift.
+  Value *X;
+  if (match(Op0, m_OneUse(m_Shr(m_Value(X), m_Specific(Op1))))) {
+    Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
+    Value *Mask = Builder.CreateShl(AllOnes, Op1);
+    return BinaryOperator::CreateAnd(Mask, X);
+  }
+
   Constant *C1;
   if (match(Op1, m_Constant(C1))) {
     Constant *C2;
Index: llvm/trunk/test/Transforms/InstCombine/canonicalize-ashr-shl-to-masking.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/canonicalize-ashr-shl-to-masking.ll
+++ llvm/trunk/test/Transforms/InstCombine/canonicalize-ashr-shl-to-masking.ll
@@ -15,8 +15,8 @@
 
 define i32 @positive_samevar(i32 %x, i32 %y) {
 ; CHECK-LABEL: @positive_samevar(
-; CHECK-NEXT:    [[TMP0:%.*]] = ashr i32 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = shl i32 [[TMP0]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl i32 -1, [[Y:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = and i32 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[RET]]
 ;
   %tmp0 = ashr i32 %x, %y
@@ -114,8 +114,8 @@
 
 define <2 x i32> @positive_samevar_vec(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @positive_samevar_vec(
-; CHECK-NEXT:    [[TMP0:%.*]] = ashr <2 x i32> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = shl <2 x i32> [[TMP0]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl <2 x i32> <i32 -1, i32 -1>, [[Y:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = and <2 x i32> [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x i32> [[RET]]
 ;
   %tmp0 = ashr <2 x i32> %x, %y
@@ -161,8 +161,7 @@
 
 define <3 x i32> @positive_sameconst_vec_undef2(<3 x i32> %x) {
 ; CHECK-LABEL: @positive_sameconst_vec_undef2(
-; CHECK-NEXT:    [[TMP0:%.*]] = ashr <3 x i32> [[X:%.*]], <i32 5, i32 undef, i32 5>
-; CHECK-NEXT:    [[RET:%.*]] = shl <3 x i32> [[TMP0]], <i32 5, i32 undef, i32 5>
+; CHECK-NEXT:    [[RET:%.*]] = and <3 x i32> [[X:%.*]], <i32 -32, i32 undef, i32 -32>
 ; CHECK-NEXT:    ret <3 x i32> [[RET]]
 ;
   %tmp0 = ashr <3 x i32> %x, <i32 5, i32 undef, i32 5>
Index: llvm/trunk/test/Transforms/InstCombine/canonicalize-lshr-shl-to-masking.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/canonicalize-lshr-shl-to-masking.ll
+++ llvm/trunk/test/Transforms/InstCombine/canonicalize-lshr-shl-to-masking.ll
@@ -15,8 +15,8 @@
 
 define i32 @positive_samevar(i32 %x, i32 %y) {
 ; CHECK-LABEL: @positive_samevar(
-; CHECK-NEXT:    [[TMP0:%.*]] = lshr i32 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = shl i32 [[TMP0]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl i32 -1, [[Y:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = and i32 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[RET]]
 ;
   %tmp0 = lshr i32 %x, %y
@@ -114,8 +114,8 @@
 
 define <2 x i32> @positive_samevar_vec(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @positive_samevar_vec(
-; CHECK-NEXT:    [[TMP0:%.*]] = lshr <2 x i32> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = shl <2 x i32> [[TMP0]], [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shl <2 x i32> <i32 -1, i32 -1>, [[Y:%.*]]
+; CHECK-NEXT:    [[RET:%.*]] = and <2 x i32> [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x i32> [[RET]]
 ;
   %tmp0 = lshr <2 x i32> %x, %y
@@ -161,8 +161,7 @@
 
 define <3 x i32> @positive_sameconst_vec_undef2(<3 x i32> %x) {
 ; CHECK-LABEL: @positive_sameconst_vec_undef2(
-; CHECK-NEXT:    [[TMP0:%.*]] = lshr <3 x i32> [[X:%.*]], <i32 5, i32 undef, i32 5>
-; CHECK-NEXT:    [[RET:%.*]] = shl <3 x i32> [[TMP0]], <i32 5, i32 undef, i32 5>
+; CHECK-NEXT:    [[RET:%.*]] = and <3 x i32> [[X:%.*]], <i32 -32, i32 undef, i32 -32>
 ; CHECK-NEXT:    ret <3 x i32> [[RET]]
 ;
   %tmp0 = lshr <3 x i32> %x, <i32 5, i32 undef, i32 5>