Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1877,6 +1877,19 @@
       }
     }
 
+    // If this 'and 'masks out high bits, we may be able to move a trunc before
+    // a shift-right. This will reduce the shift width and potentially eliminate
+    // the 'and' completely:
+    // and (trunc (lshr X, ShiftC)), C --> and (lshr (trunc X), ShiftC), C
+    if (match(Op0, m_OneUse(m_Trunc(
+                       m_OneUse(m_LShr(m_Value(X), m_APInt(ShiftC)))))) &&
+        ShiftC->ult(Width) &&
+        C->countLeadingZeros() >= ShiftC->getZExtValue()) {
+      Value *TruncX = Builder.CreateTrunc(X, Ty);
+      Value *NewShift = Builder.CreateLShr(TruncX, ShiftC->getZExtValue());
+      return BinaryOperator::CreateAnd(NewShift, Op1);
+    }
+
     const APInt *AddC;
     if (match(Op0, m_Add(m_Value(X), m_APInt(AddC)))) {
       // If we add zeros to every bit below a mask, the add has no effect:
Index: llvm/test/Transforms/InstCombine/and-narrow.ll
===================================================================
--- llvm/test/Transforms/InstCombine/and-narrow.ll
+++ llvm/test/Transforms/InstCombine/and-narrow.ll
@@ -215,9 +215,9 @@
 
 define i6 @trunc_lshr(i8 %x) {
 ; CHECK-LABEL: @trunc_lshr(
-; CHECK-NEXT:    [[S:%.*]] = lshr i8 [[X:%.*]], 2
-; CHECK-NEXT:    [[T:%.*]] = trunc i8 [[S]] to i6
-; CHECK-NEXT:    [[R:%.*]] = and i6 [[T]], 14
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i8 [[X:%.*]] to i6
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr i6 [[TMP1]], 2
+; CHECK-NEXT:    [[R:%.*]] = and i6 [[TMP2]], 14
 ; CHECK-NEXT:    ret i6 [[R]]
 ;
   %s = lshr i8 %x, 2
@@ -226,12 +226,13 @@
   ret i6 %r
 }
 
+; The 'and' is eliminated.
+
 define i6 @trunc_lshr_exact_mask(i8 %x) {
 ; CHECK-LABEL: @trunc_lshr_exact_mask(
-; CHECK-NEXT:    [[S:%.*]] = lshr i8 [[X:%.*]], 2
-; CHECK-NEXT:    [[T:%.*]] = trunc i8 [[S]] to i6
-; CHECK-NEXT:    [[R:%.*]] = and i6 [[T]], 15
-; CHECK-NEXT:    ret i6 [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i8 [[X:%.*]] to i6
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr i6 [[TMP1]], 2
+; CHECK-NEXT:    ret i6 [[TMP2]]
 ;
   %s = lshr i8 %x, 2
   %t = trunc i8 %s to i6
@@ -239,6 +240,8 @@
   ret i6 %r
 }
 
+; negative test - a high bit of x is in the result
+
 define i6 @trunc_lshr_big_mask(i8 %x) {
 ; CHECK-LABEL: @trunc_lshr_big_mask(
 ; CHECK-NEXT:    [[S:%.*]] = lshr i8 [[X:%.*]], 2
@@ -252,6 +255,8 @@
   ret i6 %r
 }
 
+; negative test
+
 define i6 @trunc_lshr_use1(i8 %x) {
 ; CHECK-LABEL: @trunc_lshr_use1(
 ; CHECK-NEXT:    [[S:%.*]] = lshr i8 [[X:%.*]], 2
@@ -267,6 +272,8 @@
   ret i6 %r
 }
 
+; negative test
+
 define i6 @trunc_lshr_use2(i8 %x) {
 ; CHECK-LABEL: @trunc_lshr_use2(
 ; CHECK-NEXT:    [[S:%.*]] = lshr i8 [[X:%.*]], 2
@@ -282,11 +289,13 @@
   ret i6 %r
 }
 
+; splat vectors are ok
+
 define <2 x i7> @trunc_lshr_vec_splat(<2 x i16> %x) {
 ; CHECK-LABEL: @trunc_lshr_vec_splat(
-; CHECK-NEXT:    [[S:%.*]] = lshr <2 x i16> [[X:%.*]], <i16 5, i16 5>
-; CHECK-NEXT:    [[T:%.*]] = trunc <2 x i16> [[S]] to <2 x i7>
-; CHECK-NEXT:    [[R:%.*]] = and <2 x i7> [[T]], <i7 1, i7 1>
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc <2 x i16> [[X:%.*]] to <2 x i7>
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr <2 x i7> [[TMP1]], <i7 5, i7 5>
+; CHECK-NEXT:    [[R:%.*]] = and <2 x i7> [[TMP2]], <i7 1, i7 1>
 ; CHECK-NEXT:    ret <2 x i7> [[R]]
 ;
   %s = lshr <2 x i16> %x, <i16 5, i16 5>
@@ -295,12 +304,13 @@
   ret <2 x i7> %r
 }
 
+; The 'and' is eliminated.
+
 define <2 x i7> @trunc_lshr_vec_splat_exact_mask(<2 x i16> %x) {
 ; CHECK-LABEL: @trunc_lshr_vec_splat_exact_mask(
-; CHECK-NEXT:    [[S:%.*]] = lshr <2 x i16> [[X:%.*]], <i16 6, i16 6>
-; CHECK-NEXT:    [[T:%.*]] = trunc <2 x i16> [[S]] to <2 x i7>
-; CHECK-NEXT:    [[R:%.*]] = and <2 x i7> [[T]], <i7 1, i7 1>
-; CHECK-NEXT:    ret <2 x i7> [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc <2 x i16> [[X:%.*]] to <2 x i7>
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr <2 x i7> [[TMP1]], <i7 6, i7 6>
+; CHECK-NEXT:    ret <2 x i7> [[TMP2]]
 ;
   %s = lshr <2 x i16> %x, <i16 6, i16 6>
   %t = trunc <2 x i16> %s to <2 x i7>
@@ -308,6 +318,8 @@
   ret <2 x i7> %r
 }
 
+; negative test - the high bit of x is in the result
+
 define <2 x i7> @trunc_lshr_big_shift(<2 x i16> %x) {
 ; CHECK-LABEL: @trunc_lshr_big_shift(
 ; CHECK-NEXT:    [[S:%.*]] = lshr <2 x i16> [[X:%.*]], <i16 7, i16 7>