diff --git a/lib/Support/KnownBits.cpp b/lib/Support/KnownBits.cpp
index e10f97bb751..7b94e7b9594 100644
--- a/lib/Support/KnownBits.cpp
+++ b/lib/Support/KnownBits.cpp
@@ -160,12 +160,16 @@ KnownBits KnownBits::shl(const KnownBits &LHS, const KnownBits &RHS) {
     return Known;
   }
 
-  // Minimum shift amount low bits are known zero.
-  if (RHS.getMinValue().ult(BitWidth))
-    Known.Zero.setLowBits(RHS.getMinValue().getZExtValue());
-
   // No matter the shift amount, the trailing zeros will stay zero.
-  Known.Zero.setLowBits(LHS.countMinTrailingZeros());
+  unsigned MinTrailingZeros = LHS.countMinTrailingZeros();
+
+  // Minimum shift amount low bits are known zero.
+  if (RHS.getMinValue().ult(BitWidth)) {
+    MinTrailingZeros += RHS.getMinValue().getZExtValue();
+    MinTrailingZeros = std::min(MinTrailingZeros, BitWidth);
+  }
+
+  Known.Zero.setLowBits(MinTrailingZeros);
   return Known;
 }
 
@@ -183,12 +187,16 @@ KnownBits KnownBits::lshr(const KnownBits &LHS, const KnownBits &RHS) {
     return Known;
   }
 
-  // Minimum shift amount high bits are known zero.
-  if (RHS.getMinValue().ult(BitWidth))
-    Known.Zero.setHighBits(RHS.getMinValue().getZExtValue());
-
   // No matter the shift amount, the leading zeros will stay zero.
-  Known.Zero.setHighBits(LHS.countMinLeadingZeros());
+  unsigned MinLeadingZeros = LHS.countMinLeadingZeros();
+
+  // Minimum shift amount high bits are known zero.
+  if (RHS.getMinValue().ult(BitWidth)) {
+    MinLeadingZeros += RHS.getMinValue().getZExtValue();
+    MinLeadingZeros = std::min(MinLeadingZeros, BitWidth);
+  }
+
+  Known.Zero.setHighBits(MinLeadingZeros);
   return Known;
 }
 
@@ -204,8 +212,24 @@ KnownBits KnownBits::ashr(const KnownBits &LHS, const KnownBits &RHS) {
     return Known;
   }
 
-  // TODO: Minimum shift amount high bits are known sign bits.
-  // TODO: No matter the shift amount, the leading sign bits will stay.
+  // No matter the shift amount, the leading sign bits will stay.
+  unsigned MinLeadingZeros = LHS.countMinLeadingZeros();
+  unsigned MinLeadingOnes = LHS.countMinLeadingOnes();
+
+  // Minimum shift amount high bits are known sign bits.
+  if (RHS.getMinValue().ult(BitWidth)) {
+    if (MinLeadingZeros) {
+      MinLeadingZeros += RHS.getMinValue().getZExtValue();
+      MinLeadingZeros = std::min(MinLeadingZeros, BitWidth);
+    }
+    if (MinLeadingOnes) {
+      MinLeadingOnes += RHS.getMinValue().getZExtValue();
+      MinLeadingOnes = std::min(MinLeadingOnes, BitWidth);
+    }
+  }
+
+  Known.Zero.setHighBits(MinLeadingZeros);
+  Known.One.setHighBits(MinLeadingOnes);
   return Known;
 }