Index: lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnswitch.cpp
+++ lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -31,6 +31,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CodeMetrics.h"
 #include "llvm/Analysis/InstructionSimplify.h"
@@ -899,7 +900,6 @@
       if (I.mayHaveSideEffects())
         return false;
 
-    // FIXME: add check for constant foldable switch instructions.
     if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
       if (BI->isUnconditional()) {
         CurrentBB = BI->getSuccessor(0);
@@ -911,7 +911,38 @@
         // Found a trivial condition candidate: non-foldable conditional branch.
         break;
       }
-    } else {
+    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
+      // Either the Cond is a constant or we try to fold it into a constant.
+      Value *Cond = SI->getCondition();
+      if (!isa<Constant>(Cond)) {
+        Instruction *I = dyn_cast<Instruction>(Cond);
+        if (!I)
+          break;
+        const DataLayout &DL = I->getModule()->getDataLayout();
+        if (Constant *Fold = ConstantFoldInstruction(I, DL))
+          Cond = Fold;
+        else 
+          break;
+      }
+      // At this point, the switched value is a constant.
+      assert(isa<Constant>(Cond) && "Switched value must be a constant");
+      bool FoundDest = false;
+      for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
+           i != e; ++i) {
+        // The case value should have the same type as the switched value.
+        assert(i.getCaseValue()->getType() == Cond->getType() &&
+               "Switched value has different types as the case value");
+        if (Cond == i.getCaseValue()) {
+          CurrentBB = i.getCaseSuccessor();
+          FoundDest = true;
+          break;
+        }
+      }
+      // The default case is taken.
+      if (!FoundDest)
+        CurrentBB = SI->getDefaultDest();
+    } else { 
+      // We do not understand this terminator instructions.
       break;
     }
 
Index: test/Transforms/LoopUnswitch/trivial-unswitch.ll
===================================================================
--- test/Transforms/LoopUnswitch/trivial-unswitch.ll
+++ test/Transforms/LoopUnswitch/trivial-unswitch.ll
@@ -44,4 +44,54 @@
   ret i32 0
 }
 
-declare void @some_func() noreturn
\ No newline at end of file
+
+; We should not trivially unswitch on the SwitchInst. Instead, we
+; should be able to figure out that the switch can be folded into
+; a unconditional branch to %continue. Then we unswitch on the br
+; inst in %continue.
+;
+; CHECK: define i32 @test2(
+
+; This is an indication that the SwitchInst is unswitched upon,
+; i.e. an ICmpInst is generated by the EmitPreheaderBranchOnCondition
+; on the unswitched case value which leads to a trivial loop exit.
+;
+; CHECK-NOT: icmp
+; CHECK:  br i1 %cond1, label %..split_crit_edge, label %.loop_exit.split_crit_edge
+
+; CHECK:  ..split_crit_edge:                                ; preds = %0
+; CHECK:    br label %.split
+
+; CHECK:  .split:                                           ; preds = %..split_crit_edge
+; CHECK:    br label %loop_begin
+
+; CHECK:  loop_begin:                                       ; preds = %do_something, %.split
+; CHECK:    switch i32
+
+; CHECK:  continue:                                         ; preds = %loop_begin
+; CHECK:    %var_val = load i32, i32* %var
+; CHECK:    br i1 true, label %do_something, label %loop_exit
+
+define i32 @test2(i32* %var, i1 %cond1) {
+  %sub = sub i32 6, 5 
+  br label %loop_begin
+
+loop_begin:  
+  switch i32 %sub, label %continue [
+    i32 0, label %loop_exit
+    i32 1, label %continue
+  ]
+
+continue:
+  %var_val = load i32, i32* %var
+  br i1 %cond1, label %do_something, label %loop_exit
+
+do_something:
+  call void @some_func() noreturn nounwind
+  br label %loop_begin
+
+loop_exit:
+  ret i32 0
+}
+
+declare void @some_func() noreturn