Index: lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnswitch.cpp
+++ lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -415,8 +415,32 @@
   }
 
   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
-    if (BO->getOpcode() == Instruction::And ||
-        BO->getOpcode() == Instruction::Or) {
+    // Do not walk up the and/or chain for values with more than
+    // 1 bit, beause we can not reliably find a value that will
+    // simplify the original and new loops.
+    //
+    // e.g.
+    //
+    // %and = and i32 %loop_invariant, %loop_variant
+    // switch i32 %and, label %sw.default [
+    //     i32 11, label %sw.bb
+    //     i32 12, label %sw.bb1
+    // ]
+    //
+    // Once we pick a value to unswitch, we still wont be able to simplified
+    // the %and instruction in the original loop, then we do not know what
+    // value we have unswitched out of the original loop. As a result, we
+    // end up unswitching the original loop again ...
+    //
+    // In case this is an instruction working on 1 bit value, we will
+    // be able to simplify the %and to either a constant or
+    // loop-variant value. In both cases, it will not get unswitched again.
+    //
+    // This will still allow us to simplify switch(i1), even though it
+    // probably should be converted to an if-else at this point.
+    if (BO->getType()->isIntegerTy(1) &&
+        (BO->getOpcode() == Instruction::And ||
+        BO->getOpcode() == Instruction::Or)) {
       // If either the left or right side is invariant, we can unswitch on this,
       // which will cause the branch to go away in one loop and the condition to
       // simplify in the other one.
@@ -651,15 +675,22 @@
         // FIXME: scan for a case with a non-critical edge?
         Constant *UnswitchVal = nullptr;
 
-        // Do not process same value again and again.
-        // At this point we have some cases already unswitched and
-        // some not yet unswitched. Let's find the first not yet unswitched one.
-        for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
-             i != e; ++i) {
-          Constant *UnswitchValCandidate = i.getCaseValue();
-          if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
-            UnswitchVal = UnswitchValCandidate;
-            break;
+        // If this is a cond we get by walking up the chain, it must be a 1 bit value.
+        if (LoopCond != SI->getCondition()) {
+          assert(LoopCond->getType()->isIntegerTy(1) &&
+                 "Loop condition must be a 1 bit value");
+          UnswitchVal = ConstantInt::getTrue(Context);
+        } else {
+          // Do not process same value again and again.
+          // At this point we have some cases already unswitched and
+          // some not yet unswitched. Let's find the first not yet unswitched one.
+          for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
+               i != e; ++i) {
+            Constant *UnswitchValCandidate = i.getCaseValue();
+            if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
+              UnswitchVal = UnswitchValCandidate;
+              break;
+            }
           }
         }
 
Index: test/Transforms/LoopUnswitch/basictest.ll
===================================================================
--- test/Transforms/LoopUnswitch/basictest.ll
+++ test/Transforms/LoopUnswitch/basictest.ll
@@ -101,6 +101,87 @@
 ; CHECK: }
 }
 
+; Make sure we do not unswitch this loop, as we do not really know the 
+; right value for %a to unswitch on.
+;
+; CHECK: define void @and_i32_as_switch_input(i32
+; CHECK: entry:
+; This is an indication that the loop has not been unswitched.
+; CHECK-NOT: icmp
+; CHECK: br
+define void @and_i32_as_switch_input(i32 %a) #0 {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %and = and i32 %a, %i
+  switch i32 %and, label %sw.default [
+    i32 11, label %sw.bb
+    i32 12, label %sw.bb1
+  ]
+
+sw.bb:
+  br label %sw.epilog
+
+sw.bb1:
+  br label %sw.epilog
+
+sw.default:
+  br label %sw.epilog
+
+sw.epilog:
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %i, 1
+  %cmp = icmp slt i32 %inc, 1024
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
+
+; Make sure we unswitch this loop.
+;
+; CHECK: define void @and_i1_as_switch_input(i1
+; CHECK: entry:
+; This is an indication that the loop has been unswitched.
+; CHECK: icmp
+; CHECK: br
+define void @and_i1_as_switch_input(i1 %a) #0 {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %t = trunc i32 %i to i1
+  %and = and i1 %a, %t
+  switch i1 %and, label %sw.default [
+    i1 0, label %sw.bb
+    i1 1, label %sw.bb1
+  ]
+
+sw.bb:
+  br label %sw.epilog
+
+sw.bb1:
+  br label %sw.epilog
+
+sw.default:
+  br label %sw.epilog
+
+sw.epilog:
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %i, 1
+  %cmp = icmp slt i32 %inc, 1024
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
 
 declare void @incf() noreturn
 declare void @decf() noreturn