Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- lib/Transforms/Scalar/JumpThreading.cpp
+++ lib/Transforms/Scalar/JumpThreading.cpp
@@ -465,6 +465,20 @@
     return !Result.empty();
   }
 
+  // Handle Cast instructions.
+  if (CastInst *CI = dyn_cast<CastInst>(I)) {
+    ComputeValueKnownInPredecessors(CI->getOperand(0), BB, Result, Preference,
+                                    CxtI);
+    if (Result.empty())
+      return false;
+
+    // Cast the known values.
+    for (auto &R : Result)
+      R.first = ConstantExpr::getCast(CI->getOpcode(), R.first, CI->getType());
+
+    return true;
+  }
+
   PredValueInfoTy LHSVals, RHSVals;
 
   // Handle some boolean conditions.
Index: test/Transforms/JumpThreading/basic.ll
===================================================================
--- test/Transforms/JumpThreading/basic.ll
+++ test/Transforms/JumpThreading/basic.ll
@@ -476,6 +476,43 @@
 ; CHECK: }
 }
 
+
+;;; Verify that we can handle constraint propagation through cast.
+define i32 @test16(i1 %cond) {
+Entry:
+; CHECK-LABEL: @test16(
+	br i1 %cond, label %Merge, label %F1
+
+; CHECK: Entry:
+; CHECK-NEXT:  br i1 %cond, label %F2, label %Merge
+
+F1:
+	%v1 = call i32 @f1()
+	br label %Merge
+
+Merge:
+	%B = phi i32 [1, %Entry], [%v1, %F1]
+        %M = icmp eq i32 %B, 0 
+        %M1 = zext i1 %M to i32
+        %N = icmp eq i32 %M1, 1 
+	br i1 %N, label %T2, label %F2
+
+; CHECK: Merge:
+; CHECK-NOT: phi
+; CHECK-NEXT:   %v1 = call i32 @f1()
+
+T2:
+	%Q = zext i1 %M to i32
+	ret i32 %Q
+
+F2:
+	ret i32 %B
+; CHECK: F2:
+; CHECK-NEXT: phi i32
+}
+
+
+
 ; In this test we check that block duplication is inhibited by the presence
 ; of a function with the 'noduplicate' attribute.