Index: lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -227,6 +227,12 @@
 
     // Compute the KnownZero/KnownOne bits to simplify things downstream.
     computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
+
+    // If the client is only demanding bits that we know, return the known
+    // constant.
+    if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask)
+      return Constant::getIntegerValue(VTy, KnownOne);
+
     return nullptr;
   }
 
Index: test/Transforms/InstCombine/and2.ll
===================================================================
--- test/Transforms/InstCombine/and2.ll
+++ test/Transforms/InstCombine/and2.ll
@@ -126,8 +126,7 @@
 define i32 @test11(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test11(
 ; CHECK-NEXT:    [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT:    [[Y:%.*]] = add i32 [[X]], [[B:%.*]]
-; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT:    [[Z:%.*]] = and i32 [[B:%.*]], 128
 ; CHECK-NEXT:    [[W:%.*]] = mul i32 [[Z]], [[X]]
 ; CHECK-NEXT:    ret i32 [[W]]
 ;
@@ -142,8 +141,7 @@
 define i32 @test12(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test12(
 ; CHECK-NEXT:    [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT:    [[Y:%.*]] = add i32 [[X]], [[B:%.*]]
-; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT:    [[Z:%.*]] = and i32 [[B:%.*]], 128
 ; CHECK-NEXT:    [[W:%.*]] = mul i32 [[Z]], [[X]]
 ; CHECK-NEXT:    ret i32 [[W]]
 ;
@@ -158,8 +156,7 @@
 define i32 @test13(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test13(
 ; CHECK-NEXT:    [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT:    [[Y:%.*]] = sub i32 [[B:%.*]], [[X]]
-; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT:    [[Z:%.*]] = and i32 [[B:%.*]], 128
 ; CHECK-NEXT:    [[W:%.*]] = mul i32 [[Z]], [[X]]
 ; CHECK-NEXT:    ret i32 [[W]]
 ;
@@ -174,7 +171,7 @@
 define i32 @test14(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test14(
 ; CHECK-NEXT:    [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT:    [[Y:%.*]] = sub i32 [[X]], [[B:%.*]]
+; CHECK-NEXT:    [[Y:%.*]] = sub i32 0, [[B:%.*]]
 ; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 128
 ; CHECK-NEXT:    [[W:%.*]] = mul i32 [[Z]], [[X]]
 ; CHECK-NEXT:    ret i32 [[W]]