diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6383,9 +6383,10 @@
 /// If the switch is only used to initialize one or more phi nodes in a common
 /// successor block with different constant values, replace the switch with
 /// lookup tables.
-static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
+static bool switchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
                                 DomTreeUpdater *DTU, const DataLayout &DL,
-                                const TargetTransformInfo &TTI) {
+                                const TargetTransformInfo &TTI,
+                                bool UnsignedComparison) {
   assert(SI->getNumCases() > 1 && "Degenerate switch?");
 
   BasicBlock *BB = SI->getParent();
@@ -6426,10 +6427,17 @@
 
   for (SwitchInst::CaseIt E = SI->case_end(); CI != E; ++CI) {
     ConstantInt *CaseVal = CI->getCaseValue();
-    if (CaseVal->getValue().slt(MinCaseVal->getValue()))
-      MinCaseVal = CaseVal;
-    if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
-      MaxCaseVal = CaseVal;
+    if (UnsignedComparison) {
+      if (CaseVal->getValue().ult(MinCaseVal->getValue()))
+        MinCaseVal = CaseVal;
+      if (CaseVal->getValue().ugt(MaxCaseVal->getValue()))
+        MaxCaseVal = CaseVal;
+    } else {
+      if (CaseVal->getValue().slt(MinCaseVal->getValue()))
+        MinCaseVal = CaseVal;
+      if (CaseVal->getValue().sgt(MaxCaseVal->getValue()))
+        MaxCaseVal = CaseVal;
+    }
 
     // Resulting value at phi nodes for this case value.
     using ResultsTy = SmallVector<std::pair<PHINode *, Constant *>, 4>;
@@ -6524,7 +6532,7 @@
     // If the default is unreachable, all case values are s>= MinCaseVal. Then
     // we can try to attach nsw.
     bool MayWrap = true;
-    if (!DefaultIsReachable) {
+    if (!DefaultIsReachable && !UnsignedComparison) {
       APInt Res = MaxCaseVal->getValue().ssub_ov(MinCaseVal->getValue(), MayWrap);
       (void)Res;
     }
@@ -6788,7 +6796,10 @@
   // CVP. Therefore, only apply this transformation during late stages of the
   // optimisation pipeline.
   if (Options.ConvertSwitchToLookupTable &&
-      SwitchToLookupTable(SI, Builder, DTU, DL, TTI))
+      switchToLookupTable(SI, Builder, DTU, DL, TTI, false))
+    return requestResimplify();
+  if (Options.ConvertSwitchToLookupTable &&
+      switchToLookupTable(SI, Builder, DTU, DL, TTI, true))
     return requestResimplify();
 
   if (ReduceSwitchRange(SI, Builder, DL, TTI))
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -115,6 +115,45 @@
 
 }
 
+; The maximum value can be `-128`(`128`) when considering only indexed ones.
+
+define i32 @f_i8_128(i8 %c) {
+; CHECK-LABEL: @f_i8_128(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i8 [[C:%.*]], 122
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ult i8 [[SWITCH_TABLEIDX]], 7
+; CHECK-NEXT:    br i1 [[TMP0]], label [[SWITCH_LOOKUP:%.*]], label [[RETURN:%.*]]
+; CHECK:       switch.lookup:
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [7 x i32], ptr @switch.table.f_i8_128, i32 0, i8 [[SWITCH_TABLEIDX]]
+; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, ptr [[SWITCH_GEP]], align 4
+; CHECK-NEXT:    br label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    [[RETVAL_0:%.*]] = phi i32 [ [[SWITCH_LOAD]], [[SWITCH_LOOKUP]] ], [ 15, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    ret i32 [[RETVAL_0]]
+;
+entry:
+  switch i8 %c, label %sw.default [
+  i8 122, label %return
+  i8 123, label %sw.bb1
+  i8 124, label %sw.bb2
+  i8 125, label %sw.bb3
+  i8 126, label %sw.bb4
+  i8 127, label %sw.bb5
+  i8 -128, label %sw.bb6
+  ]
+
+sw.bb1: br label %return
+sw.bb2: br label %return
+sw.bb3: br label %return
+sw.bb4: br label %return
+sw.bb5: br label %return
+sw.bb6: br label %return
+sw.default: br label %return
+return:
+  %retval.0 = phi i32 [ 15, %sw.default ], [ 1, %sw.bb6 ], [ 62, %sw.bb5 ], [ 27, %sw.bb4 ], [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
+  ret i32 %retval.0
+}
+
 ; A switch used to initialize two variables, an i8 and a float.
 
 declare void @dummy(i8 signext, float)
@@ -1732,20 +1771,11 @@
 ; CHECK-LABEL: @signed_overflow2(
 ; CHECK-NEXT:  start:
 ; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i8 [[N:%.*]] to i2
-; CHECK-NEXT:    switch i2 [[TRUNC]], label [[BB1:%.*]] [
-; CHECK-NEXT:    i2 1, label [[BB6:%.*]]
-; CHECK-NEXT:    i2 -2, label [[BB4:%.*]]
-; CHECK-NEXT:    i2 -1, label [[BB5:%.*]]
-; CHECK-NEXT:    ]
-; CHECK:       bb1:
-; CHECK-NEXT:    unreachable
-; CHECK:       bb4:
-; CHECK-NEXT:    br label [[BB6]]
-; CHECK:       bb5:
-; CHECK-NEXT:    br label [[BB6]]
-; CHECK:       bb6:
-; CHECK-NEXT:    [[DOTSROA_0_0:%.*]] = phi i32 [ 4444, [[BB5]] ], [ 3333, [[BB4]] ], [ 2222, [[START:%.*]] ]
-; CHECK-NEXT:    ret i32 [[DOTSROA_0_0]]
+; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i2 [[TRUNC]], 1
+; CHECK-NEXT:    [[SWITCH_IDX_CAST:%.*]] = zext i2 [[SWITCH_TABLEIDX]] to i32
+; CHECK-NEXT:    [[SWITCH_IDX_MULT:%.*]] = mul nsw i32 [[SWITCH_IDX_CAST]], 1111
+; CHECK-NEXT:    [[SWITCH_OFFSET:%.*]] = add nsw i32 [[SWITCH_IDX_MULT]], 2222
+; CHECK-NEXT:    ret i32 [[SWITCH_OFFSET]]
 ;
 start:
   %trunc = trunc i8 %n to i2