Index: llvm/lib/Transforms/Scalar/SCCP.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/SCCP.cpp
+++ llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -649,17 +649,28 @@
       Succs[0] = true;
       return;
     }
-    ValueLatticeElement SCValue = getValueState(SI->getCondition());
-    ConstantInt *CI = getConstantInt(SCValue);
+    const ValueLatticeElement &SCValue = getValueState(SI->getCondition());
+    if (ConstantInt *CI = getConstantInt(SCValue)) {
+      Succs[SI->findCaseValue(CI)->getSuccessorIndex()] = true;
+      return;
+    }
 
-    if (!CI) {   // Overdefined or unknown condition?
-      // All destinations are executable!
-      if (!SCValue.isUnknownOrUndef())
-        Succs.assign(TI.getNumSuccessors(), true);
+    if (SCValue.isConstantRange()) {
+      const ConstantRange &Range = SCValue.getConstantRange();
+      for (const auto &Case : SI->cases()) {
+        const APInt &CaseValue = Case.getCaseValue()->getValue();
+        if (Range.contains(CaseValue))
+          Succs[Case.getSuccessorIndex()] = true;
+      }
+
+      // TODO: Determine whether default case is reachable.
+      Succs[SI->case_default()->getSuccessorIndex()] = true;
       return;
     }
 
-    Succs[SI->findCaseValue(CI)->getSuccessorIndex()] = true;
+    // Overdefined or unknown condition? All destinations are executable!
+    if (!SCValue.isUnknownOrUndef())
+      Succs.assign(TI.getNumSuccessors(), true);
     return;
   }
 
@@ -1835,8 +1846,19 @@
     BasicBlock *SingleSucc = *FeasibleSuccessors.begin();
     BranchInst::Create(SingleSucc, BB);
     TI->eraseFromParent();
+  } else if (FeasibleSuccessors.size() > 1) {
+    SwitchInstProfUpdateWrapper SI(*cast<SwitchInst>(TI));
+    for (auto CI = SI->case_begin(); CI != SI->case_end();) {
+      if (!FeasibleSuccessors.count(CI->getCaseSuccessor())) {
+        SI.removeCase(CI);
+        // Don't increment CI, as we removed a case.
+        continue;
+      }
+
+      ++CI;
+    }
   } else {
-    llvm_unreachable("Either all successors are feasible, or exactly one is");
+    llvm_unreachable("Must have at least one feasible successor");
   }
   return true;
 }
Index: llvm/test/Transforms/SCCP/switch.ll
===================================================================
--- llvm/test/Transforms/SCCP/switch.ll
+++ llvm/test/Transforms/SCCP/switch.ll
@@ -46,6 +46,7 @@
   ret i32 %phi
 }
 
+; TODO: Determine that the default destination is dead.
 define i32 @test_local_range(i32 %x) {
 ; CHECK-LABEL: @test_local_range(
 ; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[X:%.*]], 3
@@ -54,7 +55,6 @@
 ; CHECK-NEXT:    i32 0, label [[SWITCH_0:%.*]]
 ; CHECK-NEXT:    i32 1, label [[SWITCH_1:%.*]]
 ; CHECK-NEXT:    i32 2, label [[SWITCH_2:%.*]]
-; CHECK-NEXT:    i32 3, label [[SWITCH_3:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       switch.default:
 ; CHECK-NEXT:    ret i32 -1
@@ -64,8 +64,6 @@
 ; CHECK-NEXT:    ret i32 1
 ; CHECK:       switch.2:
 ; CHECK-NEXT:    ret i32 2
-; CHECK:       switch.3:
-; CHECK-NEXT:    ret i32 3
 ;
   %c = icmp ult i32 %x, 3
   call void @llvm.assume(i1 %c)
@@ -92,6 +90,7 @@
   ret i32 3
 }
 
+; TODO: Determine that case i3 is dead, even though the edge is shared?
 define i32 @test_duplicate_successors(i32 %x) {
 ; CHECK-LABEL: @test_duplicate_successors(
 ; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[X:%.*]], 3
@@ -101,8 +100,6 @@
 ; CHECK-NEXT:    i32 1, label [[SWITCH_0]]
 ; CHECK-NEXT:    i32 2, label [[SWITCH_1:%.*]]
 ; CHECK-NEXT:    i32 3, label [[SWITCH_1]]
-; CHECK-NEXT:    i32 4, label [[SWITCH_2:%.*]]
-; CHECK-NEXT:    i32 5, label [[SWITCH_2]]
 ; CHECK-NEXT:    ]
 ; CHECK:       switch.default:
 ; CHECK-NEXT:    ret i32 -1
@@ -110,8 +107,6 @@
 ; CHECK-NEXT:    ret i32 0
 ; CHECK:       switch.1:
 ; CHECK-NEXT:    ret i32 1
-; CHECK:       switch.2:
-; CHECK-NEXT:    ret i32 2
 ;
   %c = icmp ult i32 %x, 3
   call void @llvm.assume(i1 %c)
@@ -137,18 +132,17 @@
   ret i32 2
 }
 
+; Case i32 2 is dead as well, but this cannot be determined based on
+; range information.
 define internal i32 @test_ip_range(i32 %x) {
 ; CHECK-LABEL: @test_ip_range(
 ; CHECK-NEXT:    switch i32 [[X:%.*]], label [[SWITCH_DEFAULT:%.*]] [
-; CHECK-NEXT:    i32 0, label [[SWITCH_0:%.*]]
+; CHECK-NEXT:    i32 3, label [[SWITCH_3:%.*]]
 ; CHECK-NEXT:    i32 1, label [[SWITCH_1:%.*]]
 ; CHECK-NEXT:    i32 2, label [[SWITCH_2:%.*]]
-; CHECK-NEXT:    i32 3, label [[SWITCH_3:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       switch.default:
 ; CHECK-NEXT:    ret i32 -1
-; CHECK:       switch.0:
-; CHECK-NEXT:    ret i32 0
 ; CHECK:       switch.1:
 ; CHECK-NEXT:    ret i32 1
 ; CHECK:       switch.2: