Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -1752,24 +1752,6 @@
   if (match(Op1, m_c_Or(m_Specific(Op0), m_Value())))
     return Op0;
 
-  // A mask that only clears known zeros of a shifted value is a no-op.
-  Value *X;
-  const APInt *Mask;
-  const APInt *ShAmt;
-  if (match(Op1, m_APInt(Mask))) {
-    // If all bits in the inverted and shifted mask are clear:
-    // and (shl X, ShAmt), Mask --> shl X, ShAmt
-    if (match(Op0, m_Shl(m_Value(X), m_APInt(ShAmt))) &&
-        (~(*Mask)).lshr(*ShAmt).isNullValue())
-      return Op0;
-
-    // If all bits in the inverted and shifted mask are clear:
-    // and (lshr X, ShAmt), Mask --> lshr X, ShAmt
-    if (match(Op0, m_LShr(m_Value(X), m_APInt(ShAmt))) &&
-        (~(*Mask)).shl(*ShAmt).isNullValue())
-      return Op0;
-  }
-
   // A & (-A) = A if A is a power of two or zero.
   if (match(Op0, m_Neg(m_Specific(Op1))) ||
       match(Op1, m_Neg(m_Specific(Op0)))) {
@@ -1781,6 +1763,19 @@
       return Op1;
   }
 
+  // Perform simplification based on known bits:
+  // If for each bit position, either LHS or RHS is known zero -> 0
+  // If for each bit position, LHS is known zero or RHS is known one -> LHS
+  // If for each bit position, LHS is known one or RHS is known zero -> RHS
+  KnownBits LHSKnown = computeKnownBits(Op0, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
+  KnownBits RHSKnown = computeKnownBits(Op1, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
+  if ((LHSKnown.Zero | RHSKnown.Zero).isAllOnesValue())
+    return Constant::getNullValue(Op0->getType());
+  if ((LHSKnown.Zero | RHSKnown.One).isAllOnesValue())
+    return Op0;
+  if ((LHSKnown.One | RHSKnown.Zero).isAllOnesValue())
+    return Op1;
+
   if (Value *V = simplifyAndOrOfICmps(Op0, Op1, true))
     return V;
 
Index: test/Transforms/InstSimplify/AndOrXor.ll
===================================================================
--- test/Transforms/InstSimplify/AndOrXor.ll
+++ test/Transforms/InstSimplify/AndOrXor.ll
@@ -873,3 +873,28 @@
   %or = or i32 %a, %nega
   ret i32 %or
 }
+
+define i32 @zext_masked_hi(i8 %x, i32 %y) {
+; CHECK-LABEL: @zext_masked_hi(
+; CHECK-NEXT:    [[HI:%.*]] = and i32 %y, -256
+; CHECK-NEXT:    ret i32 [[HI]]
+;
+  %lo = zext i8 %x to i32
+  %hi = and i32 %y, -256
+  %or = or i32 %lo, %hi
+  %mask = and i32 %or, -256
+  ret i32 %mask
+}
+
+define i32 @zext_masked_lo(i8 %x, i32 %y) {
+; CHECK-LABEL: @zext_masked_lo(
+; CHECK-NEXT:    [[LO:%.*]] = zext i8 %x to i32
+; CHECK-NEXT:    ret i32 [[LO]]
+;
+  %lo = zext i8 %x to i32
+  %hi = and i32 %y, -256
+  %or = or i32 %lo, %hi
+  %mask = and i32 %or, 255
+  ret i32 %mask
+}
+