Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6369,6 +6369,17 @@
     }
   }
 
+  // try unsigned if the case value is signed overflow
+  if (MinCaseVal->isMinSignedValue() && MaxCaseVal->isMaxValue(true)) {
+    for (auto Case : SI->cases()) {
+      ConstantInt *CaseVal = Case.getCaseValue();
+      if (CaseVal->getValue().ult(MinCaseVal->getValue()))
+        MinCaseVal = CaseVal;
+      if (CaseVal->getValue().ugt(MaxCaseVal->getValue()))
+        MaxCaseVal = CaseVal;
+    }
+  }
+
   // Keep track of the result types.
   for (PHINode *PHI : PHIs) {
     ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
Index: llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -1538,14 +1538,11 @@
 define i32 @covered_switch_with_bit_tests(i3) {
 ; CHECK-LABEL: @covered_switch_with_bit_tests(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i3 [[TMP0:%.*]], -4
-; CHECK-NEXT:    [[SWITCH_MASKINDEX:%.*]] = zext i3 [[SWITCH_TABLEIDX]] to i8
-; CHECK-NEXT:    [[SWITCH_SHIFTED:%.*]] = lshr i8 -61, [[SWITCH_MASKINDEX]]
-; CHECK-NEXT:    [[SWITCH_LOBIT:%.*]] = trunc i8 [[SWITCH_SHIFTED]] to i1
-; CHECK-NEXT:    br i1 [[SWITCH_LOBIT]], label [[SWITCH_LOOKUP:%.*]], label [[L6:%.*]]
+; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i3 [[TMP0:%.*]], 2
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i3 [[SWITCH_TABLEIDX]], -4
+; CHECK-NEXT:    br i1 [[TMP1]], label [[SWITCH_LOOKUP:%.*]], label [[L6:%.*]]
 ; CHECK:       switch.lookup:
-; CHECK-NEXT:    [[SWITCH_TABLEIDX_ZEXT:%.*]] = zext i3 [[SWITCH_TABLEIDX]] to i4
-; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [8 x i32], [8 x i32]* @switch.table.covered_switch_with_bit_tests, i32 0, i4 [[SWITCH_TABLEIDX_ZEXT]]
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* @switch.table.covered_switch_with_bit_tests, i32 0, i3 [[SWITCH_TABLEIDX]]
 ; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, i32* [[SWITCH_GEP]], align 4
 ; CHECK-NEXT:    br label [[L6]]
 ; CHECK:       l6:
@@ -1696,11 +1693,10 @@
 ; CHECK-LABEL: @signed_overflow1(
 ; CHECK-NEXT:  start:
 ; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i8 [[N:%.*]] to i2
-; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i2 [[TRUNC]], -2
-; CHECK-NEXT:    [[SWITCH_TABLEIDX_ZEXT:%.*]] = zext i2 [[SWITCH_TABLEIDX]] to i3
-; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* @switch.table.signed_overflow1, i32 0, i3 [[SWITCH_TABLEIDX_ZEXT]]
-; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, i32* [[SWITCH_GEP]], align 4
-; CHECK-NEXT:    ret i32 [[SWITCH_LOAD]]
+; CHECK-NEXT:    [[SWITCH_IDX_CAST:%.*]] = zext i2 [[TRUNC]] to i32
+; CHECK-NEXT:    [[SWITCH_IDX_MULT:%.*]] = mul i32 [[SWITCH_IDX_CAST]], 1111
+; CHECK-NEXT:    [[SWITCH_OFFSET:%.*]] = add i32 [[SWITCH_IDX_MULT]], 1111
+; CHECK-NEXT:    ret i32 [[SWITCH_OFFSET]]
 ;
 start:
   %trunc = trunc i8 %n to i2
@@ -1732,20 +1728,11 @@
 ; 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 i32 [[SWITCH_IDX_CAST]], 1111
+; CHECK-NEXT:    [[SWITCH_OFFSET:%.*]] = add i32 [[SWITCH_IDX_MULT]], 2222
+; CHECK-NEXT:    ret i32 [[SWITCH_OFFSET]]
 ;
 start:
   %trunc = trunc i8 %n to i2
@@ -1776,11 +1763,10 @@
 ; CHECK-LABEL: @signed_overflow_negative(
 ; CHECK-NEXT:  start:
 ; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i8 [[N:%.*]] to i2
-; CHECK-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i2 [[TRUNC]], -2
-; CHECK-NEXT:    [[SWITCH_IDX_CAST:%.*]] = zext i2 [[SWITCH_TABLEIDX]] to i32
-; CHECK-NEXT:    [[SWITCH_IDX_MULT:%.*]] = mul i32 [[SWITCH_IDX_CAST]], 1111
-; CHECK-NEXT:    [[SWITCH_OFFSET:%.*]] = add i32 [[SWITCH_IDX_MULT]], 1111
-; CHECK-NEXT:    ret i32 [[SWITCH_OFFSET]]
+; CHECK-NEXT:    [[SWITCH_TABLEIDX_ZEXT:%.*]] = zext i2 [[TRUNC]] to i3
+; CHECK-NEXT:    [[SWITCH_GEP:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* @switch.table.signed_overflow_negative, i32 0, i3 [[SWITCH_TABLEIDX_ZEXT]]
+; CHECK-NEXT:    [[SWITCH_LOAD:%.*]] = load i32, i32* [[SWITCH_GEP]], align 4
+; CHECK-NEXT:    ret i32 [[SWITCH_LOAD]]
 ;
 start:
   %trunc = trunc i8 %n to i2